AASHTO-1996

STANDARD SPECIFICATIONS for HIGHWAY BRIDGES SIXTEENTH EDITION 1996

I ¶BRARY & DOCUMENTATION CENThE r~&TOUBROL~ .~TRUCT1ON GROUP ~“

£79

FOONAMALLEE ROAD ,~.KKAM, MADRAS-COO

Adopted and Published by the American Association of State Highway and Transportation Officials, Inc. 444 North Capitol Street, N.W., Suite 249 Washington, D.C. 20001

© Copyright 1996 by the American Association of State Highway and TransportationOYficials. Inc. All Rights Reserved. Printed in the United States of America. This book, or parts thereof. may not be reproduced in any form without permission of the publishers. ISBN 1-56051-040-4

AMERICAN ASSOCIATION OF STATE HIGHWAY AND TRANSPORTATION OFFICIALS EXECUTIVE COMMITTEE 1995—1996

VOTING MEMBERS Officers: President: Bill Burnett, Texas Vice President: Darrell Rensink, Iowa Secretary/Treasurer: Clyde F. Pyers, Maryland Regional Representatives: Regions:

I II III LV

Carlos I. Pesquara, Puerto Rico Robert L. Robinson, Mississippi Patrick Nowak, Michigan Marshall W. Moore, North Dakota NON-VOTING MEMBERS

immediate Past President: Wayne Shackelford, Georgia Erecutive Director: Francis B. Erancois. Washington, D.C.

H

HIGHWAY SUBCOMMITTEE ON BRIDGES AND STRUCTURES 1995 JAMES E. SIEBELS, COLORADO, Chairman G. CHARLES LEWIS, GEORGIA, Vice Chairman STANLEY GORDON, Federal Highway Administration, Secretary ALABAMA, William F. Conway ALASKA, Steve Bradford, Ray Shumway ARIZONA, William R. Brucsch, F. Daniel Davis ARKANSAS, Dale Loe CALIFORNIA, James E. Roberts COLORADO, Stephen Horton CONNECTICUT, Gordon Barton DELAWARE, Chao H. Hu D.C., Jacob Patnaik, Luke DiPompo FLORIDA, Jerry Potter GEORGIA, Paul Liles HAWAII, Donald C. Ornellas IDAHO, Scott Stokes ILLINOIS, Ralph E. Anderson INDIANA, John J. White IOWA, William A. Lundquist KANSAS, Kennth F. Hurst KENTUCKY, Richard Sutherland LOUISIANA, Norval Knapp, Wayne Aymond MAINE, Larry L. Roberts, James E. Tukey MARYLAND, Earle S. Freedman MASSACHUSETTS, Alexander K. Bardow MICHIGAN, Sudhakar Kulkarni MINNESOTA, Donald J. Flemming MISSISSIPPI, Wilbur F. Massey MISSOURI, Allen F Laffoon MONTANA, Joseph Kolman NEBRASKA, Lyman D. Freemon NEVADA, Floyd I. Marcucci NEW HAMSPHIRE, James A. Moore NEW JERSEY, Robert Pege NEW MEXICO, Martin A. Gavurnick NEW YORK, (vacant) NORTH CAROLINA, John L. Smith NORTH DAKOTA, Steven J. Miller OHIO, Richard L. Engel OKLAHOMA, Veldo M. Goins OREGON, Teriy J. Shike PENNSYLVANIA, (vacant) PUERTO RICO, Jorge L. Melendez, Hector Camacho

RHODE ISLAND, Kazem Farhoumand SOUTH CAROLINA, Rocque L. Kneece SOUTH DAKOTA, John Cole TENNESSEE, Clellon Loveall, Ed Wasserman TEXAS, Robert Wilson U.S. DOT, Stanley Gordon (FHWA), Nick E. Mpars (USCG) UTAH, Dave Christensen VERMONT, Warren B. Tripp VIRGINIA, Malcolm T. Kerley WASHINGTON, Myint Lwin WEST VIRGINIA, James Sothen WISCONSIN, Stanley W. Woods WYOMING, David Pope ALBERTA, Bob Ramsay BRITISH COLUMBIA, Peter Brett MANITOBA, W. Saltzbcrg MARIANA ISLANDS, Elizabeth H. Salas-Balajadia NEW BRUNSWICK, G.A. Rushton NEWFOUNDLAND, Peter Lester NORTHWEST TERRITORIES, Jivko Jivkov NOVA SCOTIA, Al MacRae ONTARIO, Ranjit S. Reel SASKATCHEWAN, Lorne J. Hamblin MASS. METRO. DIST. COMM., David Lenhardt N.J. TURNPIKE AUTHORITY, Wallace R. Grant PORT AUTH. OF NY AND NJ, Joseph K. Kelly NY STATE BRIDGE AUTHORITY, William Moreau BUREAU OF INDIAN AFFAIRS, Wade Cosey U.S. DEPARTMENT OF AGRICULTUREFOREST SERVICE, Nelson Hernandez MILITARY TRAFHC MANAGEMENT COMMAND, Robert D. Franz U.S. ARMY CORPS OF ENGINEERSDEPT. OF THE ARMY, Paul C. T. Tan

iii

PREFACE to Sixteenth Edition Major changes and revisions to this edition are as follows: I. The Interim Specifications of 1993, 1994, 1995, and 1996 have been adopted and are included. (Note the 1996 interim, with commentary, were never published as a separate document.) 2. Entire Division I-A, Seismic Design, was revised. Entire sectionof Commentary and Supplements A & B of Division I-A were deleted. 3. Section 17, Soil-Reinforced Concrete Structure Interaction Systems, of Division I was revised. 4. Section 26, Metal Culverts, of Division It was revised. 5. Section 27, Concrete Culverts, of Division II was revised. 6. Section 29, Embedment Anchors, was added to Division II.

iv

INTRODUCTION The compilation of these specifications began in 1921 with the organization of the

Committee on Bridges and Structures of the American Association of State Highway Officials. During the period from 1921, until printed in 1931, the specifications were gradually developed, and as the several divisions were approved from time to time, they were made available in mimeographed form for use of the State Highway Departments and other organizations. A complete specification was available in 1926 and it was revised in 1928. Though not in printed form, the specifications were valuable to the bridge engineering profession during the period of development. The first edition of the Standard Specifications was published in 193 I, and it was followed by the 1935, 1941, 1944, 1949, 1953, 1957, 1961, 1965, 1969, 1973, 1977, 1983, 1989, and 1992 revised editions. The present sixteenth edition constitutes a revision of the 1992 specifications, including those changes adopted since the publication of the fifteenth edition and those through 1995. The constant research and development in steel, concrete, and timber structures practically dictates the necessity of revising the specifications every few years, and the 1996 edition continues this trend. Interim Specifications are usually published in the middle of the calendar year, and a revised edition of this book is generally published every 4 years. The Interim Specifications have the same status as standards of the American Association of State Highway and Transportation Officials, but are tentative revisions approved by at least twothirds of the Subcommittee on Bridges and Structures. These revisions are voted on by the Association Member Departments prior to the publication of each new edition of this book, and if approved by at least two-thirds of the members, they are included in the new edition as standards of the Association. Members of the Association are the 50 State Highway or Transportation Departments, the District of Columbia, and Puerto Rico. Each member has one vote. The U.S. Department of Transportation is a nonvoting member. Annual Interim Specifications are generally used by the States after their adoption by the Bridge Subcommittee. Orders for these annual Interim Specifications should be sent to the Publication Sales Office of the Association at 444 North Capitol Street, N.W., Suite 249, Washington, D.C. 20001, (202)624-5800. The Standard Specifi cations for Highway Bridges are intended to serve as a standard or guide for the preparation of State specifications and for reference by bridge engineers. Primarily, the specifications set forth minimum requirements which are consistent with current practice, and certain modifications may be necessary to suit local condi-

tions. They apply to ordinary highway bridges and supplemental specifications may be required for unusual types and for bridges with spans longer than 500 feet. Specifications of the American Society for Testing and Materials, the American Welding Society, the American Wood Preservers Association, and the National Forest

Products Association are referred to, or are recognized. Numerous research bulletins are noted for references.

The American Association of State Highway and Transportation Officials wishes to express its sincere appreciation to the above organizations, as well as to those universities and representatives of industry whose research efforts and consultations have been most helpful in continual improvement of these specifications. Extensive references have been made to the Standard Specifications for Tramisporration Materials published by the American Association of State Highway and Transportation Officials, including equivalent ASTM specifications which have been reproduced in the Association’s Standard Specifications by permission of the American Society for Testing and Materials. Attention is also directed to the following publications prepared and published by

the Bridge Subcommittee: v

Construction Manual for Highway Bridges and Incidental Structures—1973 Edition Guide Specificationsfor Fracture Critical Non-Redundant Steel Bridge Members—1978 Edition, updated to 1986 Guide Specificationsfor Horizontally Curved Highway Bridges—1980 Edition, updated to 1993 Standard Specifications for Movable Highway Bridges— 1988 Edition Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals—1985 Edition, updated to 1994 Guide Specifications for Alternate Load Factor Design Procedures for Steel Beam Bridges Using Braced Compact Sections—199 1 Edition AASHTO Commentary on ANSI/AASHTO/AWS Bridge Welding Code D].5-88— 1991 Edition Guide Specifications for Strength Design of Truss Bridges (Load Factor Design)— 1986 Edition Guide Spec(fications for Fatigue Evaluation of Existing Steel Bridges—1990 Edition Guide Specifications for Strength Evaluation of Existing Steel and Concrete Bridges— 1989 Edition Guide Specifications for Design and Construction and Segmental Concrete Bridges—1989 Edition Guide Specifications for Bridge Railings—1989 Edition Guide Specifications for Structural Design of Sound Barriers—1989 Edition AASHTO Guide Specifications—Thermal Effects in Concrete Bridge Superstructure—I 989 Edition ANSI/AASHTO/AWS Bridge Welding Code DJ.5 Foundation Investigation Manual—1978 Edition Guide Specification and Commentary for Vessel Collision Design of Highway Bridges— 1991 Edition Guide Specification for the Design of Stress-Laminated Wood Decks—1991 Edition Guidelines for Bridge Management Svstems—1993 Edition

Manualfor Condition Evaluation ofBridges—1994 Edition Guide Specifications for Distribution of Loads for Highway Bridges—1994

Edition Guide Specifications for Aluminum Highway Bridges— 1991 Edition Guide Specifications for Seismic Isolation Design—1991 Edition Guide Specifications for Fatigue Design of Steel Bridges—1989 Edition

vi

AASHTO LRFD Bridge Design Specifications—1994 U.S. Units Edition, 1994

SI Units Edition Guide Design Specifications for Bridge Temporary Work— 1995 Edition Construction Handbook for Bridge Temporary Work— 1995 Edition

Guide for Painting Steel Structures—1996 Edition The following have served as chairmen of the Committee since its inception in 1921: Messrs, E.F. Kelley, who pioneered the work of the Committee, Albin L. Gemeny, R. B. McMinn, Raymond Archiband, G. S. Paxson, E. M. Johnson, Ward Goodman, Charles Matlock, Joseph S. Jones, Sidney Poleynard, Jack Freidenrich, Henry W. Derthick, Robert C. Cassano, Clellon Loveall, and James E. Siebels. The Committee expresses its sincere appreciation of the work of these men and of those active members of the past, whose names, because of retirement, are no longer on the roll. Suggestions for the improvement of the specifications are welcomed. They should be sent to the Chairman, Subcommittee on Bridges and Structures, AASHTO, 444 North Capitol Street, N.W., Suite 249, Washington, D.C. 20001. Inquiries as to the intent or application of the specifications should be sent to the same address.

ABBREVIATIONS AASHTO ACI AITC ASCE ASTM ANSI AWS AWPA CS NDS NFPA SAF WPA WWPA

—American Association of State Highway and Transportation Officials —American Concrete Institute

—American Institute of Timber Construction —American Society of Civil Engineers —American Society for Testing and Materials —American National Standards Institute —American Welding Society —American Wood Preservers Association —Commercial Standards —National Design Specifications for Stress Grade Lumber and Its Fastenings —National Forest Products Association —Society of Automotive Engineers —Western Pine Association

—Western Wood Products Association

vii

AASHTO STANDARD SPECIFICATIONS TABLE OF CONTENTS DIVISION I DESIGN SECTION I—GENERAL PROVISIONS 1.1 1.1.1 1.1.2 1.2 1.3

1.3.1 1.3.2

1.3.2.1 1.3.2.2 1.3.2.3 1.4 1.5

1.6 1.6.1 1.6.2 1.7 1.8

1.9

DESIGN ANALYSIS AND GENERAL STRUCTURAL INTEGRITY FOR BRIDGES Design Analysis Structural Integrity BRIDGE LOCATIONS WATERWAYS General Hydraulic Studies Site Data Hydrologic Analysis . .

.

3 3 3 3 3 3 4

.

.

Hydraulic Analysts

.

4 4

..

CULVERT LOCATION, LENGTH, AND WATERWAY OPENINGS ROADWAY DRAINAGE RAILROAD OVERPASSES Clearances Blast Protection SUPERELEVATION FLOOR SURFACES UTILITIES .

.

..

.

.4 4

4 4 4

4 S 5 5

SECTION 2—GENERAL FEATURES OF DESIGN 2.1 2.1.1 2.1.2

2.2 2.2.1

2.2.2 2.2.3 9 2.4 2.2.5 2.3 2.3.1 2.3.2 24 241 ~) 4

2

2.4.3

25 2.5.1 2.5.2 2.5.3 2.5.4 2.6

GENERAL Notations Width of Roadway and Sidewalk STANDARD HIGHWAY CLEARANCES—GENERAL Navigational Roadway Width Vertical Clearance Other Curbs and Sidewalks HIGHWAY CLEARANCES FOR BRIDGES Width Vertical Clearance HIGHWAY CLEARANCES FOR UNDERPASSES Width Vertical Clearance Curbs HIGHWAY CLEARANCES FOR TUNNELS Roadway Width. Clearance Between Walls Vertical Clearance Curbs HIGHWAY CLEARANCES FOR DEPRESSED ROADWXYS .

....

..

...

.

..

.

\ 111

.

.

7 7 7 7 7 7 7 7

8 8 8 8 8 8 8 8 8 8 10 10

10 10

Division I

ix

CONTENTS 2.6.1 2.6.2 2.6.3 2.7 2.7.1 2.7.1.1 2.7.1.2 2.7.1.3

2.7.2 2.7.2.1 2.7.2.2 2.7.3 2.7.3.1 2.7.3.2 2.7.4

Roadway Width Clearance Between Wails Curbs RAILINGS Vehicular Railing General

10 10 10 10 10 10

Geometry Loads

10

11 11 11 II 12 12 13

Bicycle Railing General Geometry and Loads Pedestrian Railing General Geometry and Loads Structural Specifications and Guidelines

13

SECTION 3—LOADS PART A—TYPES OF LOADS 3.1

NOTATIONS

3.2 3.3 3.4 3.5

GENERAL DEAD LOAD LIVE LOAD OVERLOAD PROVISIONS TRAFFIC LANES HIGHWAY LOADS Standard Truck and Lane Loads Classes of Loading Designation of Loadings Minimum Loading HLoading HSLoading IMPACT Application

3.6

3.7 3.7.1 3.7.2 3.7.3 3.7 4 375 376

3.8 3.8.1 3.8.1.1

3.8.1.2 3.8.2 3.9

3.10 3.11 3.11.1 3.11.2

3.11.3 3.11.4 3.12 3.13 3.14

3 14 1 3.14.2 3.14.3 3.15

17

19

..

19 20

...

GroupA

GroupB Impact Formula LONGITUDINAL FORCES CENTRIFUGAL FORCES APPLICATION OF LIVE LOAD Traffic Lane Units Number and Position of Traffic Lane Units Lane Loads on Continuous Spans Loading for Maximum Stress REDUCTION IN LOAD INTENSITY ELECTRIC RAILWAY LOADS SIDEWALK, CURB, AND RAILING LOADING Sidewalk Loading Curb Loading Railing Loading WINDLOADS .

.

.

.

.

..

.

.

20 20 20 20 21 21 21 21 21 21 21 21 21 21 23 25 25 25 25 25 25 25 25 26 26

26 26 26

x

CONTENTS 3.15.1 3.15.1.1 3.15.1.2

3.15.2 3.15.2.1 3.15.2.2 3.15.3 3.16 3.17

3.18 3. 18.1 3.18.1.1 3.18.1.2 3.18.1.3 3.18.2 3.18.2.1 3.18.2.2 3.18.2.3 3.19 3.20 3.21

Division I

Superstructure Design Group II and Group V Loadings Group III and Group VI Loadings

Substructure Design Forces from Superstructure Forces Applied Directly to the Substructure Overturning Forces THERMAL FORCES UPLIFT FORCES FROM STREAM CURRENT, FLOATING ICE, AND DRIFT CONDITIONS Force of Stream Current on Piers Stream Pressure Pressure Components Drift Lodged Against Pier Force of Ice on Piers General Dynamic Ice Force Static Ice Pressure BUOYANCY EARTH PRESSURE EARTHQUAKES .

.

..

26 26 26 26

27 27 27 27 28 28 28

28 28 28 28 28 29 29 31 31 31

PART B—COMBINATIONS OF LOADS 3.22

COMBINATIONS OF LOADS

31

PART C—DISTRIBUTION OF LOADS 3.23 3.23.1 3.23.2 3.23.2.1

3.23.2.2 3.23.2.3 3.23.2.3.1 3.23.2.3.2 3.23.2.3.3 3.23.3 3.23.4 3.24

DISTRIBUTION OF LOADS TO STRINGERS, LONGITUDINAL BEAMS, AND FLOOR BEAMS Position of Loads for Shear Bending Moments in Stringers and Longitudinal Beams General

33

Interior Stringers and Beams Outside Roadway Stringers and Beams Steel-Timber-Concrete T-Beams Concrete Box Girders Total Capacity of Stringers and Beams Bending Moments in Floor Beams (Transverse) Precast Concrete Beams Used in Multi-Beam Decks DISTRIBUTION OF LOADS AND DESIGN OF CONCRETE SLABS Span Lengths Edge Distance of Wheel Loads Bending Moment Case A—Main Reinforcement Perpendicular to Traffic (Spans 2 to 24 Feet Inclusive) Case B—Main Reinforcement Parallel to Traffic Shear and Bond Cantilever Slabs Truck Loads Case A—Reinforcement Perpendicular to Traffic Case B—Reinforcement Parallel to Traffic ...

3.24.1 3.24.2 3.24.3 3.24.3.1 3.24.3.2 3.24.4 3.24.5 3.24.5.1 3.24.5.1.1 3.24.5. 1.2

32 32 33

.

.

.

33 33 33 33 33 33 34

35 35 35

36 36 36 36 36 36 36

Division I

xi

CONTENTS 3.24.5.2 3.24.6

3.24.7

3.24.8 3.24.9 3.24.10 3.25

3.25.1 3.25.2 3.25.3 3.25.3.1 3.25.3.2 3.25.3.3 3.25.3.4 3.25.4 3.26 3.26.1

3.26.2 3.26.3 3.27

Railing Loads Slabs Supported on Four Sides Median Slabs Longitudinal Edge Beams Unsupported Transverse Edges Distribution Reinforcement DISTRIBUTION OF WHEEL LOADS ON TIMBER FLOORING Transverse Flooring Plank and Nail Laminated Longitudinal Flooring Longitudinal Glued Laminated Timber Decks Bending Moment Shear Deflections Stiffener Arrangement Continuous Flooring DISTRIBUTION OF WHEEL LOADS AND DESIGN OF COMPOSITE WOOD-CONCRETE MEMBERS Distribution of Concentrated Loads for Bending Moment and Shear Distribution of Bending Moments in Continuous Spans Design DISTRIBUTION OF WHEEL LOADS ON STEEL GRID FLOORS.. General Floors Filled with Concrete Open Floors DISTRIBUTION OF LOADS FOR BENDING MOMENT IN SPREAD BOX GIRDERS Interior Beams Exterior Beams MOMENTS, SHEARS, AND REACTIONS TIRE CONTACT AREA ..

.

..

....

.

.

...

3.28.1 3.28.2 3.29 3.30

36

. .

..

3.27.1 3.27.2 3.27.3 3.28

36

.

.

.

..

.

..

37 37 37 37 .37 37 39 39 39 39 40 40

40 40 40

40 40 40

40 41

41 41 41 41

41 41

SECTION 4—FOUNDATIONS PART A—GENERAL REQUIREMENTS AND MATERIALS 4.1 4.2 4.2.1 4.2.2 4.2.2.1 4.2.2.2 4.2.2.3

4.2.3 4.3

GENERAL FOUNDATION TYPE AND CAPACITY Selection of Foundation Type Foundation Capacity Bearing Capacity .

..

..

Settlement Overall Stability

43 43

Soil, Rock, and Other Problem Conditions SUBSURFACE EXPLORATION AND TESTING PROGRAMS General Requirements Minimum Depth Minimum Coverage Laboratory Testing Scour .

4.3.1 4.3.2 4.3.3 4.3.4 4.3.5

43 43 43 43 43

43 43

.

43 44

45 45 45

xii

Division I

CONTENTS PART B—SERVICE LOAD DESIGN METHOD ALLOWABLE STRESS DESIGN 4.4 4.4.1 4.4.1.1 4.4.1.2 4.4.1.3 4.4.1.4 4.4.1.5 4.4.2 4.4.3 4.4.4 4.4.5 4.4.5.1 4.4.5.2 4.4.5.3

4.4.5.4 4.4.6 4.4.7 4.4.7.1

4.4.7. 1.1 4.4.7.1.1.1 4.4.7.1.1.2 4.4.7.1.1.3 4.4.7.1.1.4

4.4.7.1.1.5 4.4.7.1.1.6 4.4.7.1. 1.7 4.4.7.1.1.8

4.4.7.1.2 4.4.7.2 4.4.7.2.1 4.4.7.2.2 4.4.7.2.3 4.4.7.2.4 4.4.7.2.5 4.4.7.3

4.4.8 4.4.8.1 4.4.8. 1.1 4.4.8.1.2 4.4.8.1.3 4.4.8.2 4.4.8.2.1

SPREAD FOOTINGS General Applicability Footings Supporting Non-Rectangular Columns or Piers Footings in Fill ....

Footings in Sloped Portions of Embankments

Distribution of Bearing Pressure Notations Design Terminology Soil and Rock Property Selection Depth Minimum Embedment and Bench Width Scour Protection Footing Excavations Piping

Ground Water Layered Soils Inclined Base Factors of Safety Settlement Stress Distribution

Elastic Settlement Consolidation Settlement Secondary Settlement Tolerable Movement Dynamic Ground Stability Geotechnical Design on Rock Bearing Capacity Footings on Competent Rock Footings on Broken or Jointed Rock Factors of Safety Settlement Footings on Competent Rock Footings on Broken or Jointed Rock Tolerable Movement

4.4.11.1

Loads and Reactions

4.4.11.1.1 4.4.11. 1.2

45 45 45

48 ...

....

Overall Stability Dynamic/Seismic Design Structural Design

45 45 45 45

48 48

Anchorage Geotechnical Design on Soil Bearing Capacity Factors Affecting Bearing Capacity Eccentric Loading Footing Shape Inclined Loading Ground Surface Slope Embedment Depth

4.4.8.2.2 4.4.8.2.3 4.4.9 4.4.10 4.4.11

45

Action of Loads and Reactions Isolated and Multiple Footing Reactions

48 49 49 49 49 49

49 50 50 51 51 51 51

5 55 57 57 57 57 58 58 61 61 61 61 62 62 62 63 63 63 63 64 64 66 66 66

.66 67

Division I

CONTENTS 4.4.11.2 4.4.11.2.1 4.4.11.2.2 4.4.11.3 4.4.11.3.1 4.4.11.3.2 4.4.11.4 4.4.11.4.1 4.4.11.4.2 4.4.11.5 4.4.11.5.1 4.4.11.5.2 4.4.11.5.3 4.4.11.5.4 4.4.11.5.5 4.4.11.5.6 4.4.11.5.7 4.4.11.6 4.4.11.6.1 4.4.11.6.2 4.5 4.5.1 4.5.1.1 4.5.1.2 4.5.1.3 4.5.1.4 4.5.1.5 4.5.1.6 4.5.1.7 4.5.1.8 4.5.2 4.5.2.1

4.5.2.2 4.5.2.3 4.5.2.4 4.5.3 4.5.4

4.5.5 4.5.6 4.5.6.1 4.5.6.1.1 4.5.6.1.2 4.5.6.1.3 4.5.6.1.4 4.5.6.2 4.5.6.3 4.5.6.4 4.5.6.5 4.5.6.6 4.5.6.6.1 4.5.6.6.2 4.5.6.7 4.5.6.7.1

Moments Critical Section Distribution of Reinforcement Shear Critical Section Footings on Piles or Drilled Shafts Development of Reinforcement Development Length Critical Section Transfer of Force at Base of Column Transfer of Force Lateral Forces Bearing Reinforcement Dowel Size Development Length Splicing Unreinforced Concrete Footings Design Stress Pedestals DRIVEN PILES General Application Materials Penetration Lateral Tip Restraint Estimated Lengths Estimated and Minimum Tip Elevation Piles Through Embankment Fill Test Piles Pile Types Friction Piles

End Bearing Piles Combination Friction and End Bearing Piles Batter Piles Notations Design Terminology Selection of Soil and Rock Properties Selection of Design Pile Capacity Ultimate Geotechnical Capacity Factors Affecting Axial Capacity Axial Capacity in Cohesive Soils Axial Capacity in Cohesionless Soils Axial Capacity on Rock Factor of Safety Selection Settlement Group Pile Loading Lateral Loads on Piles Uplift Loads on Piles Single Pile Pile Group Vertical Ground Movement Negative Skin Friction

xiii 67 67 67 67 67 67 67 67 67 67 67 67 68 68 68 68 68 68

68 68 68 68

68 68 68 69 69 69 69 69 69 69

69 69 69 69 70 70 70 70 70 70 70 70 71 71 71 72 72 72 72 72 72

CONTENTS

xiv 4.5.6.7.2

4.5.6.8 4.5.7 4.5.7.1 4.5.7.2 4.5.7.3 4.5.7.4 4.5.7.5

4.5.8 4.5.9 4.5.10 4.5.11

4.5.12 4.5.13

4.5.14 4.5.14.1 4.5.14.2 4.5.14.3 4.5.15 4.5.15.1

4.5.15.1.1 4.5.15.1.2 4.5.15.2 4.5.16 4.5.16.1 4.5.16.2 4.5.16.3 4.5.16.4 4.5.16.5 4.5.16.6

4.5.16.7 4.516.8 4.5.16.9

4.5.17 4.5.17.1 4.5.17.2 4.5.17.3 4.5.17.4 4.5.17.5 4.5.17.6 4.5.17.7 4.5.17.8 4.5.18 4.5.18.1 4.5.18.2 4.5.18.3 4.5.18.4 4.5.18.5 4.5.19 4.5.19.1 4.5.19.2 4.5.19.3 4.5.19.4

Expansive Soil Dynamic/Seismic Design Structural Capacity of Pile Section Load Capacity Requirements Piles Extending Above Ground Surface Allowable Stress in Piles Cross-Section Adjustment for Corrosion Scour Protection Against Corrosion and Abrasion Wave Equation Analysis Dynamic Monitoring Maximum Allowable Driving Stresses Tolerable Movement Buoyancy Protection Against Deterioration Steel Piles Concrete Piles Timber Piles Spacing, Clearances, and Embedment Pile Footings

Pile Spacing Minimum Projection into Cap Bent Caps Precast Concrete Piles Size and Shape MinimumArea Minimum Diameter of Tapered Piles Driving Points Vertical Reinforcement Spiral Reinforcement

Reinforcement Cover Splices Handling Stresses Cast-in-Place Concrete Piles Materials Shape Minimum Area General Reinforcement Requirements Reinforcement into Superstructure Shell Requirements Splices Reinforcement Cover Steel H-Piles Metal Thickness Splices Caps Lugs, Scabs, and Core-Stoppers Point Attachments Unfilled Tubular Steel Piles Metal Thickness Splices Driving Column Action

Division I 72 73 73 73 73 73 73 74 74 74 74 74

74 74 74

74 75 75 75 75

75 75 75 75 75 75 75 75 75 75

76 76 76 76

76 76 76 76 76 76 76 76 76 76 76 77 77 77 77 77 77 77 77

Division I

CONTENTS 4.5.20

4.5.20.1 4.5 .20.2 4.5.20.3 4.5.20.4 4.5.20.5 4.5.21 4.5.21.1 4.5.2 1.2 4.5.21.3 4.6 4.6.1 4.6.1. 1 4.6.1.2 4.6.1.3 4.6.1.4 4.6.1.5

4.6.1.6 4.6.1.7 4.6.2 4.6.3 4.6.4 4.6.4.1 4.6.4.2 4.6.5 4.6.5.1

Prestressed Concrete Piles

Size and Shape Main Reinforcement Vertical Reinforcement Hollow Cylinder Piles Splices Timber Piles Materials Limitations on Untreated Timber Pile Use Limitations on Treated Timber Pile Use DRILLED SHAFTS General Application Materials Construction Embedment .

.

Shaft Diameter

Batter Shafts Shafts Through Embankment Fill Notations Design Terminology Selection of Soil and Rock Properties Presumptive Values Measured Values Geotechnical Design Axial Capacity in Soil

4.6.5.1. I

Side Resistance in Cohesive Soil

4.6.5.1.2

Side Resistance in Cohesionless Soil

4.6.5.1.3 4.6.5.1.4 4.6.5.2 4.6.5.2.1 4.6.5.2.2 4.6.5.2.3 4.6.5.2.4 4.6.5.2.4.1 4.6.5.2.4.2 4.6.5.2.4.3 4.6.5.2.5 4.6.5.2.6 4.6.5.3 4.6.5.3. I 4.6.5.3.2 4.6.5.3.3

4.6.5.3.3.1 4.6.5.3.3.2 4.6.5.3.3.3 4.6.5.4 4.6.5.5 4.6.5.5.1 4.6.5.5.1.1 4.6.5.5.1.2 4.6.5.5.1.3

Tip Resistance in Cohesive Soil Tip Resistance in Cohesionless Soil Factors Affecting Axial Capacity in Soil Soil Layering and Variable Soil Strength with Depth Ground Water Enlarged Bases Group Action Cohesive Soil Cohesionless Soil Group in Strong Soil Overlying Weaker Soil Vertical Ground Movement Method of Construction Axial Capacity in Rock Side Resistance Tip Resistance Factors Affecting Axial Capacity in Rock

Rock Stratification Rock Mass Discontinuities Method of Construction Factors of Safety Deformation of Axially Loaded Shafts Shafts in Soil Cohesive Soil Cohesionless Soil Mixed Soil Profile

xv

77 77 77 77 78 78 78 78 78 78 78 78 78 78 78 78 78

78 79 79 80 80 80 80 80 80 81 81

82 83 83 83 83 83 83 83 84 84 84 84 84 85 85 85

85 86 86 86 86 86 86 86 87

xvi

CONTENTS 4.6.5.5.2 Shafts Socketed into Rock 4.6.5.5.3 Tolerable Movement 4.6.5.6 Lateral Loading 4.6.5.6.1 Factors Affecting Laterally Loaded Shafts 4.6.5.6.1.1 Soil Layering 4.6.5.6.1.2 Ground Water 4.6.5.6.1.3 Scour 4.6.5.6.1.4 Group Action 4.6.5.6.1.5 Cyclic Loading 4.6.5.6.1.6 Combined Axial and Lateral Loading 4.6.5.6.1.7 Sloping Ground 4.6.5.6.2 Tolerable Lateral Movements 4.6.5.7 Dynamic/Seismic Design 4.6.6 Structural Design and General Shaft Dimensions 4.6.6.1 General 4.6.6.2 Reinforcement 4.6.6.2.1 Longitudinal Bar Spacing 4.6.6.2.2 Splices 4.6.6.2.3 Transverse Reinforcement 4.6.6.2.4 Handling Stresses 4.6.6.2.5 Reinforcement Cover 4.6.6.2.6 Reinforcement into Superstructure 4.6.6.3 Enlarged Bases 4.6.6.4 Center-to-Center Shaft Spacing 4.6.7 Load Testing 4.6.7.1 General 4.6.7.2 Load Testing Procedures 4.6.7.3 Load Test Method Selection 4.7 NOTE: Article Number Intentionally Not Used

Division I 87 87 88 88 88 88 88 88 89 89 89 89 90 90 90 90 90 90 90 90 90 90 90 91 91 91 91 91

PART C—STRENGTH DESIGN METHOD LOAD FACTOR DESIGN 4.8 4.9 4.10 4.10.1 4.10.2 4.10.3 4.10.4 4.10.5 4.10.6 4.11 4.11.1 4.11.1.1 4.11.1.2 4.11.1.3 4.11.1.4 4.11.1.5 4.11.1.6 4.11.1.7 4.11 .1.8 4.11.1.9

SCOPE DEFINITIONS LIMIT STATES, LOAD FACTORS, AND RESISTANCE FACTORS General Serviceability Limit States Strength Limit States Strength Requirement Load Combinations and Load Factors Performance Factors SPREAD FOOTINGS General Considerations General Depth Scour Protection Frost Action Anchorage Groundwater Uplift Deterioration Nearby Structures .

91 92 92 92 92 92 93 93 93 93 93 93 93 93 93 93 94 94 94 95

Division I

CONTENTS 4.11.2 Notations 4.11.3 Movement Under Serviceability Limit States 4.11.3.1 General 4.11.3.2 Loads 4.11.3.3 Movement Criteria 4.11.3.4 Settlement Analyses 4.11.3.4.1 Settlement of Footings on Cohesionless Soils 4.11.3.4.2 Settlement of Footings on Cohesive Soils 4.11.3.4.3 Settlement of Footings on Rock 4.11.4 Safety Against Soil Failure 4.11.4.1 Bearing Capacity of Foundation Soils 4.11.4.1.1 Theoretical Estimation 4.11.4.1.2 Semi-Empirical Procedures 4.11.4.1.3 Plate Loading Test 4.11.4.1.4 Presumptive Values 4.11.4.1.5 Effect of Load Eccentricity 4.11.4.1.6 Effect of Groundwater Table 4.11.4.2 Bearing Capacity of Foundations on Rock 4.11.4.2.1 Semi-Empirical Procedures 4.11.4.2.2 Analytic Method 4.11.4.2.3 LoadTest 4.11.4.2.4 Presumptive Bearing Values 4.11.4.2.5 Effect of Load Eccentricity 4.11.4.3 Failure by Sliding 4.11.4.4 Loss of Overall Stability 4.11.5 Structural Capacity 4.11.6 Construction Considerations for Shallow Foundations. 4.11.6.1 General 4.11.6.2 Excavation Monitoring 4.11.6.3 Compaction Monitoring 4.12 DRIVEN PILES 4.12.1 General 4.12.2 Notations 4.12.3 Selection of Design Pile Capacity 4.12.3.1 Factors Affecting Axial Capacity 4.12.3.1.1 Pile Penetration 4.12.3.1.2 Groundwater Table and Buoyancy 4.12.3.1.3 Effect of Settling Ground and Downdrag Forces 4.12.3.1.4 Uplift 4.12.3.2 Movement Under Serviceability Limit State 4.12.3.2.1 General 4.12.3.2.2 Tolerable Movement 4.12.3.2.3 Settlement 4.12.3.2.3a Cohesive Soil 4.12.3.2.3b Cohesionless Soil 4.12.3.2.4 Lateral Displacement 4.12.3.3 Resistance at Strength Limit States 4.12.3.3.1 Axial Loading of Piles 4.12.3.3.2 Analytic Estimates of Pile Capacity 4.12.3.3.3 Pile of Capacity Estimates Based on In Situ Tests 4.12.3.3.4 Piles Bearing on Rock 4.12.3.3.5 PileLoadTest 4.12.3.3.6 Presumptive End Bearing Capacities 4.12.3.3.7 Uplift ....

xvii 95 97 97 97 97 97 97 97 97 97 97 98 98 98 98 98 98 98 98 100 100 100 100 100 100 100 100 100 100 100 100 100 101 102 102 102 102 102 103 103 103 103 103 103 103 103 103 103 104 104 104 104 104 104

xviii

CONTENTS 4.12 7a 4.12.3.3.7b 4. 12.3.3.8 4. 12.3.3.9 4. 12.3.3. 10 4. 12.3.3. lOa 4. 12.3.3. lOb 4. 12.3.3. lOc 4.12.3.3.11 4.12.4 4. 12.4. 4.12.5 4.13 4.13.1 4.13.2 4.13.3 4. 13.3.1 4.13.3.1.1 4. 13.3. 1.2 4.13.3.2 4.13.3.2.1 4.13.3.2.2 4.13.3.2.3 4. 13.3.2.3a 4.1 3.3.2.3b 4.13.3.2.4 4.13.3.3 4. 13.3.3. 1 4.13.3.3.2 4.13.3.3.3 4.13.3.3.4 4.13.3.3.5 4. 13.3.3.6 4.13.3.3.6a 4. 13.3.3.6b 4.13.3.3.7 4.13.3.3.8 4.13.3.3.8a 4.13.3.3.8b 4.13.3.3.8c 4.13.3.3.9 4.13.4 4.13.4.1

Single Pile Uplift Capacity Pile Group Uplift Capacity Lateral Load Batter Pile Group Capacity Cohesive Soil Cohesionless Soil Pile Group in Strong Soil Overlying a Weak or Compressible Soil Dynamic/Seismic Design Structural Design Buckling of Piles Construction Considerations DRILLED SHAFTS General Notations Geotechnical Design Factors Affecting Axial Capacity Downdrag Loads Uplift Movement Under Serviceability Limit State General Tolerable Movement Settlement Settlement of Single Drilled Shafts Group Settlement Lateral Displacement Resistance at Strength Limit States Axial Loading of Drilled Shafts Analytic Estimates of Drilled Shaft Capacity in Cohesive Soils Estimation of Drilled-Shaft Capacity in Cohesionless Soils Axial Capacity in Rock Load Test Uplift Capacity Uplift Capacity of a Single Drilled Shaft Group Uplift Capacity Lateral Load Group Capacity Cohesive Soil Cohesionless Soil Group in Strong Soil Overlying Weaker Compressible Soil Dynamic/Seismic Design Structural Design Buckling of Drilled Shafts

Division I 104 104 104 104 104 104 105 105 105 105 105 105 105 105 105 106 107 107 107 107 107 107 107 107 107 107 107 107

....

107 107 107 108 108 108 108 108 108 108 108 108 108 108 109

SECTION 5—RETAINING WALLS PART A—GENERAL REQUIREMENTS AND MATERIALS 5.1 5.2

GENERAL WALLTYPEAND CAPACITY

111 111

Division I

CONTENTS 5.2.1

5.2.1.1 5.2.1.2 5.2.1.3 5.2.1.4 5.2.1.5 5.2.2 5.2.2.1 5.2.2.2 5.2.2.3 5.2.2.4 5.2.3 5.3 5.3.1 5.3.2 5.3.3 5.3.4 5.3.5 5.4

xix

Selection of Wall Type Rigid Gravity and Semi-Gravity Walls Nongravity Cantilevered Walls Anchored Walls Mechanically Stabilized Earth Walls Prefabricated Modular Walls Wall Capacity Bearing Capacity Settlement Overall Stability Tolerable Movements Soil, Rock, and Other Problem Conditions SUBSURFACE EXPLORATION AND TESTING PROGRAMS General Requirements Minimum Depth Minimum Coverage Laboratory Testing Scour NOTATIONS .

...

.

Ill 111 Ill 112 112 112 113 113 113 113 113 113 .113 113 114 114 114 114 114

PART B—SERVICE LOAD DESIGN METHOD ALLOWABLE STRESS DESIGN 5.5 5.5.1 5.5.2 5.5.3 5.5.4 5.5.5 5.5.6 5.5.6.1 5.5.6.2 5.5.6.3 5.5.6.4 5.5.6.5 5.5.7 5.5.8 5.6 5.6.1

5.6.2 5.6.3 5.6.4 5.6.5 5.6.6

5.6.7 5.6.8 5.7 5.7.1 5.7.2 5.7.3 5.7.4

5.7.5 5.7.6

RIGID GRAVITY AND SEMI-GRAVITY WALL DESIGN Design Terminology Earth Pressure and Surcharge Loadings Water Pressure and Drainage Seismic Pressure Structure Dimensions and External Stability Structure Design Base or Footing Slabs Wall Stems Counterforts and Buttresses Reinforcement Expansion and Contraction Joints Backfill Overall Stability NONGRAVITY CANTILEVERED WALL DESIGN Design Terminology Earth Pressure and Surcharge Loadings Water Pressure and Drainage Seismic Pressure Structure Dimensions and External Stability Structure Design Overall Stability Corrosion Protection ANCHORED WALL DESIGN Design Terminology Earth Pressure and Surcharge Loadings Water Pressure and Drainage Seismic Pressure Structure Dimensions and External Stability Structure Design .

116 116 116 119 120 123 123 123 123 123 125 125 125 125 125 125 125 127 127 127 129 129 129 129 129 129 130 131 131 132

xx

CONTENTS 5.7.6.1 5.7.6.2 5.7.7 5.7.8 5.7.9 5.8 5.8.1 5.8.2 5.8.3 5.8.4 5.8.4.1 5.8.4.2 5.8.5 5.8.6 5.8.6.1 5.8.6.2 5.8.7 5.8.7.1 5.8.7.2 5.8.8 5.8.9 5.8.10 5.8. 10.1 5.8. 10.2 5.8.11 5.9 5.9.1 5.9.2 5.9.3 5.9.4 5.9.5

Division I

General Anchor Design Overall Stability Corrosion Protection Anchor Load Testing and Stressing MECHANICALLY STABILIZED EARTH WALL DESIGN Structure Dimensions External Stability Bearing Capacity and Foundation Stability Internal Stability Inextensible Reinforcements Extensible Reinforcements Pullout Design Parameters Design Life Requirements Steel Reinforcement Polymeric Reinforcement Allowable Stresses Steel Reinforcements Polymeric Reinforcements Drainage Special Loading Conditions Seismic Design External Stability Internal Stability Structural Requirements PREFABRICATED MODULAR WALL DESIGN Structure Dimensions External Stability Bearing Capacity and Foundation Stability Allowable Stresses Drainage ...

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...

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132 133 133 133 133 134 134 134 136 138 138 139 139 139 139 140 141 141 141 141 141 142 142 142 142 142 142 143 143 143 144

PART C—STRENGTH DESIGN METHOD LOAD FACTOR DESIGN 5.10 5.11 5.12 5.13 5.13. I 5.13.2 5.13.3 5.13.4 5.13.5 5.14 5.14.1 5.14.2 5.14.3 5.14.4 5.14.5 5.14.6 5.14.6.1

SCOPE DEFINITIONS NOTATIONS LIMIT STATES, LOAD FACTORS AND RESISTANCE FACTORS Serviceability Limit States Strength Limit States Strength Requirement Load Combinations and Load Factors Performance Factors GRAVITY AND SEMI-GRAVITY WALL DESIGN, AND CANTILEVER WALL DESIGN Earth Pressure Due to Backfill Earth Pressure Due to Surcharge Water Pressure and Drainage Seismic Pressure Movement Under Serviceability Limit States Safety Against Soil Failure Bearing Capacity Failure

144 144 146 146 146 146 146 146 147 147 147 147 147 148 148 148 148

Division I

xxi

CONTENTS 5.14.6.2 5.14.6.3 5.14.6.4 5.14.7 5.14.7.1 5.14.7.2 5.14.7.3 5.14.7.4 5.14.7.5 5.14.8

Sliding Overturning Overall Stability Safety Against Structural Failure BaseofFootingSlabs Wall Stems Counterforts and Buttresses Reinforcement Expansion and Contraction Joints Backfill

150 150 150 ISO 150 150 150 150 150 151

SECTION 6—CULVERTS 6.1 6.2 6.2.1 6.2.2 6.3 6.4

CULVERT LOCATION, LENGTH, AND WATERWAY OPENINGS DEAD LOADS Culvert in trench, or culvert untrenched on yielding foundation.. Culvert untrenched on unyielding foundation FOOTINGS DISTRIBUTION OF WHEEL LOADS THROUGH EARTH FILLS DISTRIBUTION REINFORCEMENT DESIGN .

6.5 6.6

.

...

153 153 .153 153 153 153 153 153

SECTION 7—SUBSTRUCTURES PART A—GENERAL REQUIREMENTS AND MATERIALS 7.1 7.1.1 7.1.2 7.1.3 7.1.4 7.2

GENERAL Definition Loads Settlement Foundation and Retaining Wall Design NOTATIONS

155 155 155 155 155 155

PART B—SERVICE LOAD DESIGN METHOD ALLOWABLE STRESS DESIGN 7.3 7.3.1 7.3.1.1 7.3.1.2 7.3.1.3. 7.3.1.4 7.3.2 7.3.2.1 7.3.2.2 7.3.2.3 7.3.2.4 74 7.4.1 7.4.2 7.S 7.5.1

PIERS PierTypes Solid Wall Piers Double Wall Piers Bent Piers Single-Column Piers Pier Protection Collision Collision Walls Scour Facing TUBULAR PIERS Materials Configuration ABUTMENTS AbutmentTypes .

.

155 155 155 155 156 156 156 156 156 156 156 156 1S6 1S6 1S6 156

xxii

CONTENTS 7.5.1.1 7.5.1.2 7.5.1.3 7.5.1.4 7.5.2 7.5.2.1 7.5.2.2 7.5.2.3 7.5.3 7.5.4 7.5.5 7.5.6 7.5.6.1 7.5.6.2

Division I

StubAbutment Partial-Depth Abutment Full-Depth Abutment Integral Abutment Loading Stability Reinforcement for Temperature Drainage and Backfilling Integral Abutments Abutments on Mechanically Stabilized Earth Walls Abutments on Modular Systems Wingwalls Length Reinforcement

156 156 156 157 157 157 157 157 157 157 159 159 159 160

PART C—STRENGTH DESIGN METHOD LOAD FACTOR DESIGN 7.6

GENERAL

160

SECTION 8—REINFORCED CONCRETE PART A—GENERAL REQUIREMENTS AND MATERIALS 8.1 8.1.1 8.1.2 8.1.3 8.2 8.3

APPLICATION General Notations Definitions CONCRETE REINFORCEMENT

161 161 161 164 164 165

.

PART B—ANALYSIS 8.4 8.5 8.6 8.7 8.8 8.9 8.9.1 8.9.2 8.9.3 8.10 8.10.1 8.10.2 8.11 8.12 8.13

GENERAL EXPANSION AND CONTRACTION STIFFNESS MODULUS OF ELASTICITY AND POISSON’S RATIO SPAN LENGTH CONTROL OF DEFLECTIONS General Superstructure Depth Limitations Superstructure Deflection Limitations COMPRESSION FLANGE WIDTH T-Girder Box Girders SLAB AND WEB THICKNESS DIAPHRAGMS COMPUTATION OF DEFLECTIONS .

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165 165 165 165 165 166 166 166 166 166 166 166 166 167 167

PART C—DESIGN 8.14 8.14.1

GENERAL Design Methods

167 167

Division I

CONTENTS 8.14.2 8.14.3 8.15 8.15.1 8.15.2 8.15.2.1 8.15.2.1.1 8.15.2.1.2 8.15.2.1.3 8.15.2.2 8.15.3 8.15.4 8.15.5 8.15.5.1 8.15.5.2 8.15.5.2.1 8.15.5.2.2 8.15.5.2.3 8.15.5.2.4 8.15.5.3 8.15.5.4 8.15.5.4.3 8.15.5.5

Composite Flexural Members Concrete Arches SERVICE LOAD DESIGN METHOD (Allowable Stress Design) General Requirements Allowable Stresses Concrete Flexure Shear Bearing Stress Reinforcement Flexure Compression Members Shear Shear Stress Shear Stress Carried by Concrete Shear in Beams and One-Way Slabs and Footings Shear in Compression Members Shear in Tension Members Shear in Lightweight Concrete Shear Stress Carried by Shear Reinforcement Shear Friction Shear-Friction Design Method Horizontal Shear Design for Composite Concrete Flexural Members 8.15.5.5.5 Ties for Horizontal Shear 8.15.5.6 Special Provisions for Slabs and Footings 8.15.5.7 Special Provisions for Slabs of Box Culverts 8.15.5.8 Special Provisions for Brackets and Corbels 8.16 STRENGTH DESIGN METHOD (Load Factor Design) 8.16.1 Strength Requirements 8.16.1.1 Required Strength 8.16.1.2 Design Strength 8.16.2 Design Assumptions 8.16.3 Fiexure 8.16.3. 1 Maximum Reinforcement of Flexural Members 8.16.3.2 Rectangular Sections with Tension Reinforcement Only 8.16.3.3 Flanged Sections with Tension Reinforcement Only 8.16.3.4 Rectangular Sections with Compression Reinforcement 8.16.3.5 Other Cross Sections 8.16.4 Compression Members 8.16.4.1 General Requirements 8.16.4.2 Compression Member Strengths 8.16.4.2.1 Pure Compression 8.16.4.2.2 PureFlexure 8.16.4.2.3 Balanced Strain Conditions 8.16.4.2.4 Combined Flexure and Axial Load 8.16.4.3 Biaxial Loading 8.16.5 Slenderness Effects in Compression Members 8.16.5.1 General Requirements 8.16.5.2 Approximate Evaluation of Slenderness Effects 8.16.6 Shear 8.16.6.1 Shear Strength 8.16.6.2 Shear Strength Provided by Concrete ....

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.

xxiii

.

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168 168 169 169 169 169 169 169 169 169 169 169 170 170 170 170 170 170 170 171 171 171 172 172 172 173 173 174 174 174 174 174 175 175 175 175 176 176 176 176 176 176 177 177 177 177 177 177 177 178 178 179

xxiv

CONTENTS 8.16.6.2.1 8.16.6.2.2 8.16.6.2.3 8.16.6.2.4 8.16.6.3 8.16.6.4 8.16.6.4.4 8.16.6.5

8.16.6.5.5 8.16.6.6 8.16.6.7 8.16.6.8 8.16.7 8.16.8 8.16.8.1 8.16.8.2 8.16.8.3 8.16.8.4

Division I

Shear in Beams and One-Way Slabs and Footings Shear in Compression Members Shear in Tension Members Shear in Lightweight Concrete Shear Strength Provided by Shear Reinforcement Shear Friction Shear-Friction Design Method Horizontal Shear Strength for Composite Concrete Flexural Members Ties for Horizontal Shear Special Provisions for Slabs and Footings Special Provisions for Slabs of Box Culverts Special Provisions for Brackets and Corbels Bearing Strength Serviceability Requirements Application Service Load Stresses Fatigue Stress Limits Distribution of Flexural Reinforcement

179 179 179 179 179 180 180 181 181 181 182 182 183 183 183 183 183 184

PART D—REINFORCEMENT 8.17 8.17.1 8.17.2 8.17.2.1 8.17.2.2 8.17.2.3 8.17.3 8.18 8.1 8.1 8.18.2 8.18.2.1 8.18.2.2 8.18.2.3 8.18.2.4 8.19 8.19.1 8.19.2 8.19.3 8.20 8.21 8.22 8.23 8.23.1 8.23.2 8.24 8.24.1 8.24.2 8.24.3 8.25 8.26

REINFORCEMENT OF FLEXURAL MEMBERS Minimum Reinforcement Distribution of Reinforcement Flexural Tension Reinforcement in Zones of Maximum Tension... Transverse Deck Slab Reinforcement in T-Girders and Box Girders Bottom Slab Reinforcement for Box Girders Lateral Reinforcement of Flexural Members REINFORCEMENT OF COMPRESSION MEMBERS Maximum and Minimum Longitudinal Reinforcement Lateral Reinforcement General Spirals Ties Seismic Requirements LIMITS FOR SHEAR REINFORCEMENT Minimum Shear Reinforcement Types of Shear Reinforcement Spacing of Shear Reinforcement SHRINKAGE AND TEMPERATURE REINFORCEMENT SPACING LIMITS FOR REINFORCEMENT PROTECTION AGAINST CORROSION HOOKS AND BENDS Standard Hooks Minimum Bend Diameters DEVELOPMENT OF FLEXURAL REINFORCEMENT General Positive Moment Reinforcement Negative Moment Reinforcement DEVELOPMENT OF DEFORMED BARS AND DEFORMED WIRE IN TENSION DEVELOPMENT OF DEFORMED BARS IN COMPRESSION .

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184 184 184 .184 185 185 185 185 185 186 186 186 186 186 186 186 187 187 187 187 187 188 188 188 188 188 189 189 189 190

Division I

CONTENTS 8.27 8.28 8.29 8.30 8.30.1 8.30.2 8.31 8.32 8.32.1 8.32.2 8.32.3 8.32.4 8.32.4.1 8.32.4.2 8.32.4.3 8.32.5 8.32.6

xxv

DEVELOPMENT OF SHEAR REINFORCEMENT DEVELOPMENT OF BUNDLED BARS DEVELOPMENT OF STANDARD HOOKS IN TENSION DEVELOPMENT OF WELDED WIRE FABRIC IN TENSION Deformed Wire Fabric Smooth Wire Fabric MECHANICAL ANCHORAGE SPLICES OF REINFORCEMENT Lap Splices Welded Splices and Mechanical Connections Splices of Deformed Bars and Deformed Wire in Tension Splices of Bars in Compression Lap Splices in Compression End-Bearing Splices Welded Splices or Mechanical Connections Splices of Welded Deformed Wire Fabric in Tension Splices of Welded Smooth Wire Fabric in Tension

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.

191 191 191 .192 192 193 193 193 193 193 193 194 194 194 194 194 194

SECTION 9—PRESTRESSED CONCRETE PART A—GENERAL REQUIREMENTS AND MATERIALS 9.1 9.1.1 9.1.2 9.1.3 9.2 9.3 9.3.1 9.3.2

APPLICATION General Notations Definitions CONCRETE REINFORCEMENT Prestressing Steel Non-Prestressed Reinforcement

195 195 195 197 198 198 198 198

PART B—ANALYSIS 9.4 9.5 9.6 9.7 9.7.1 9.7.2 9.7.2.1 9.7.2.2 9.7.2.3 9.7.3 9.7.3.1 9.7.3.2 9.7.3.3 9.8 9.8.1 9.8.2 9.8.3 9.9 9.9.1

GENERAL EXPANSION AND CONTRACTION SPAN LENGTH FRAMES AND CONTINUOUS CONSTRUCTION Cast-in-Place Post-Tensioned Bridges Bridges Composed of Simple-Span Precast Prestressed Girders Made Continuous General Positive Moment Connection at Piers Negative Moments Segmental Box Girders General Flexure Torsion EFFECTIVE FLANGE WIDTH T-Beams Box Girders Precast/Prestressed Concrete Beams with Wide Top Flanges FLANGE AND WEB THICKNESS—BOX GIRDERS Top Flange .

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198 198 198 198 198 199 199 199 199 199 199 199 199 199 199 199 200 200 200

xxvi

CONTENTS 9.9.2 9.9.3 9.10 9.10.1 9.10.2 9.10.3 9.11 9.11.1 9.11.2 9.11.3 9.12 9.12.1 9.12.2

Division I

Bottom Flange Web DIAPHRAGMS General T-Beams Box Girders DEFLECTIONS General. Segmental Box Girders Superstructure Deflection Limitations DECKPANELS General Bending Moment .

.

.

200 200 200 200 200 200 200 200 201 201 201 201 201

PART C—DESIGN 9.13 9.13.1 9.13.2 9.13.3 9.14 9.15 9.15.1 9.15.2 9.15.2.1 9.15.2.2 9.15.2.3 9.15.2.4 9.16 9.16.1 9.16.2 9.16.2.1 9.16.2.1.1 9.16.2.1.2 9.16.2.1.3 9.16.2.1.4 9.16.2.2 9.17 9.17.1 9.17.2 9.17.3 9.17.4 9.18 9.18.1 9.18.2 9.19 9.20 9.20.1 9.20.2 9.20.3 9.20.4 9.20.4.5

GENERAL.. Design Theory and General Considerations Basic Assumption Composite Flexural Members LOAD FACTORS ALLOWABLE STRESSES Prestressing Steel. Concrete Temporary Stresses Before Losses Due to Creep and Shrinkage Stress at Service Load After Losses Have Occurred Cracking Stress Anchorage Bearing Stress LOSS OF PRESTRESS Friction Losses Prestress Losses General Shrinkage Elastic Shortening Creep of Concrete Relaxation of Prestressing Steel Estimated Losses FLEXURAL STRENGTH General Rectangular Sections Flanged Sections Steel Stress DUCTILITY LIMITS Maximum Prestressing Steel Minimum Steel NON-PRESTRESSED REINFORCEMENT SHEAR General Shear Strength Provided by Concrete Shear Strength Provided by Web Reinforcement Horizontal Shear Design—Composite Flexural Members Ties for Horizontal Shear ...

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201 201 201 201 202 202 202 202 202 202 203 203 203 203 203 203 203 204 204 204 206 206 206 206 206 207 207 207 207 207 208 208 208 209 209 209

Division I

CONTENTS 9.21 9.21.1

9.21.2 9.21.2.1 9.21.2.2 9.21.2.3 9.21.3 9.21.3.1 9.21.3.2 9.21.3.3 9.21.3.4 9.21.3.5 9.21.3.6 9.21.3.7 9.21.4 9.21.4.1 9.21.4.2 9.21.4.3 9.21.4.4 9.21.5 9.21.6 9.21.6.1 9.21.6.2 9.21.6.3 9.21.6.4 9.21.7 9.21.7.1 9.21.7.2 9.2 1.7.3 9.22 9.23 9.24

xxvu

POST-TENSIONED ANCHORAGE ZONES Geometry of the Anchorage Zone General Zone and Local Zone General Zone Local Zone Responsibilities DesignoftheGeneralZone Design Methods Nominal Material Strengths Use of Special Anchorage Devices General Design Principles and Detailing Requirements Intermediate Anchorages Diaphragms Multiple Slab Anchorages Application of Strut-and-Tie Models to the Design of Anchorage Zones General Nodes Struts Ties Elastic Stress Analysis Approximate Methods Limitations Compressive Stresses Bursting Forces Edge-Tension Forces Design of the Local Zone Dimensions of the Local Zone Bearing Strength Special Anchorage Devices PRETENSIONED ANCHORAGE ZONES CONCRETE STRENGTH AT STRESS TRANSFER DECK PANELS ...

.

210 210 210 210 210 210 210 210 211 211 211 212 213 213 213 213 214 214 214 214 214 214 214 215 215 216 216 216 217 217 217 217

PART D—DETAILING 9.25 9.26 9.26.1 9.26.2 9.26.3 9.26.4 9.27 9.28 9.29

FLANGE REINFORCEMENT COVER AND SPACING OF STEEL Minimum Cover Minimum Spacing Bundling Size of Ducts POST-TENSIONING ANCHORAGES AND COUPLERS EMBEDMENT OF PRESTRESSED STRAND BEARINGS .

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218 218 218 218 218 218 218 21 8A 218A

SECTION 10—STRUCTURAL STEEL PART A—GENERAL REQUIREMENTS AND MATERIALS 10.1 10.1.1

APPLICATION Notations ..

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219 219

xxviii

CONTENTS 10.2 10.2.1

10.2.2 10.2.3 10.2.4 10.2.5 10.2.6 10.2.6.1 10.2.6.2 10.2.6.3 10.2.6.4

Division I

MATERIALS General Structural Steels Steels for Pins, Rollers, and Expansion Rockers Fasteners—Rivets and Bolts Weld Metal Cast Steel, Ductile Iron Castings, Malleable Castings, Cast Iron, and Bronze or Copper Alloy Cast Steel and Ductile Iron Malleable Castings Cast Iron Bronze or Copper Alloy ...

.

223 223 223 223 223 223 225 925 225 225 225

PART B—DESIGN DETAILS 10.3

REPETITIVE LOADING AND TOUGHNESS CONSIDERATIONS Allowable Fatigue Stress Load Cycles Charpy V-Notch Impact Requirements Shear EFFECTIVE LENGTH OF SPAN DEPTH RATIOS DEFLECTION LIMITING LENGTHS OF MEMBERS MINIMUM THICKNESS OF METAL EFFECTIVE AREA OF ANGLES AND TEE SECTIONS IN TENSION OUTSTANDING LEGS OF ANGLES EXPANSION AND CONTRACTION FLEXURAL MEMBERS COVER PLATES CAMBER HEAT-CURVED ROLLED BEAMS AND WELDED PLATE GIRDERS Scope Minimum Radius of Curvature Camber TRUSSES General Truss Members Secondary Stresses Diaphragms Camber Working Lines and Gravity Axes Portal and Sway Bracing Perforated Cover Plates Stay Plates Lacing Bars Gusset Plates Half-Through Truss Spans Fastener Pitch in Ends of Compression Members Net Section of Riveted or High-Strength Bolted Tension Members .

10.3.1 10.3.2 10.3.3 10.3.4 10.4 10.5 10.6 10.7 10.8 10.9 10.10 10.11 10.12 10.13 10.14 10.15 10.15.1 10.15.2 10.15.3 10.16 10.16.1 10.16.2 10.16.3 10.16.4 10.16.5 10.16.6 10.16.7 10.16.8 10.16.9 10.16.10 10.16.11 10.16.12 10.16.13 10.16.14

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.

225 225 225 225 26 26 26 226 231 231 232 232 232 32 232 233 233 233 233 233 234 234 234 234 234 235 235 235 235 235 236 236 236 237 237

Division I

CONTENTS 10.17 10.17.1 10.17.2 10.17.3 10.17.4 10.17.5 10.18 10.18.1 10.18.2 10.18.3 10.18.4 10.18.5 10.18.6 10.19 10.19.1 10.19.2 10.19.3 10.20 10.20.1 10.20.2 10.20.2.1 10.20.2.2 10.20.3 10.21 10.22 10.23 10.23.1 10.23.2 10.23.2.1 10.23.2.2 10.23.3 10.23.4 10.23.5 10.24 10.24.1 10.24.2 10.24.3 10.24.4 10.24.5 10.24.5.1 10.24.5.2 10.24.5.3 10.24.5.4 10.24.6 10.24.6.1 10.24.6.2 10.24.7 10.24.7.1 10.24.8 10.25 10.25.1

xxix

BENTS AND TOWERS General SingleRents Batter Bracing Bottom Struts SPLICES General BeamsandGirders Columns Tension Members Welding Fillers STRENGTH OF CONNECTIONS General End Connections of Floor Beams and Stringers End Connections of Diaphragms and Cross Frames DIAPHRAGMS AND CROSS FRAMES General Stresses Due to Wind Loading When Top Flanges are Continuously Supported Flanges Diaphragms and Cross Frames Stresses Due to Wind Load When Top Flanges are not Continuously Supported LATERAL BRACING CLOSED SECTIONS AND POCKETS WELDING General Effective Size of Fillet Welds Maximum Size of Fillet Welds Minimum Size of Fillet Welds Minimum Effective Length of Fillet Welds Fillet Weld End Returns Seal Welds FASTENERS (Rivets and Bolts) General. Hole Types Washer Requirements Size of Fasteners (Rivets or High-Strength Bolts) Spacing of Fasteners Pitch and Gage of Fasteners Minimum Spacing of Fasteners Minimum Clear Distance Between Holes Maximum Spacing of Fasteners Maximum Spacing of Sealing and Stitch Fasteners Sealing Fasteners Stitch Fasteners Edge Distance of Fasteners General Long Rivets LINKS AND HANGERS Net Section ..

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...

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.

237 237 237 237 237 238 238 238 238 238 239 239 239 239 239 239 240 241 241 241 241 241 241 241 242 242 242 242 242 242 242 242 242 243 243 243 244 244 244 244 245 245 245 245 245 245 245 245 246 246 246

xxx

CONTENTS 10.25.2 10.25.3 10.25.4 10.25.5 10.26 10.27 10.27.1 10.27.2 10.28 10.29 10.29.1 10.29.2 10.29.3 10.29.4 10.29.5 10.29.6 10.29.7 10.30 10.30.1 10.30.2 10.30.3 10.30.4 10.30.5 10.30.6 10.30.7 10.30.8 10.30.8.1 10.30.8.2

Division I

Location of Pins Size of Pins Pin Plates Pins and Pin Nuts UPSET ENDS EYEBARS Thickness and Net Section Packing of Eyebars FORKED ENDS FIXED AND EXPANSION BEARINGS General Bronze or Copper-Alloy Sliding Expansion Bearings Rollers Sole Plates and Masonry Plates Masonry Bearings Anchor Bolts Pedestals and Shoes FLOOR SYSTEM Stringers Floor Beams Cross Frames Expansion Joints End Floor Beams End Panel of Skewed Bridges Sidewalk Brackets Stay-in-Place Deck Forms Concrete Deck Panels Metal Stay-in-Place Forms .

.

...

246 246 246 246 246 246 246 247 247 247 247 247 247 247 247 247 248 248 248 248 248 248 248 248 248 248 248 248

PART C—SERVICE LOAD DESIGN METHOD ALLOWABLE STRESS DESIGN 10.31 10.32 10.32.1 10.32.2 10.32.3 10.32.3.1 10.32.3.3 10.32.3.4 10.32.4 10.32.5 10.32.5.1 10.32.5.2 10.32.5.3 10.32.5.4 10.32.6 10.33 10.33.1 10.33.2 10.34

SCOPE ALLOWABLE STRESSES Steel Weld Metal Fasteners (Rivets and Bolts) General Applied Tension, Combined Tension and Shear Fatigue Pins, Rollers, and Expansion Rockers Cast Steel, Ductile Iron Castings, Malleable Castings, and Cast Iron Cast Steel and Ductile Iron Malleable Castings Cast Iron Bronze or Copper-Alloy Bearing on Masonry ROLLED BEAMS General Bearing Stiffeners PLATE GIRDERS ..

..

.

249 249 249 249 249 249 253 254 254 255 255 255 255 255 255 256 256 256 256

Division I

xxxi

CONTENTS 10.34.1 10.34.2 10.34.2.1 10.34.2.2 10.34.3 10.34.3.1 10.34.3.2 10.34.4 10.34.5 10.34.6 10.34.6.1 10 34 6 2 10 35 10.35.1 10.35.2 10.36 10.37 10.37.1 10.37.2 10.37.3 10.38 10.38.1 10.38.2 10.38.3 10.38.4 10.38.5 10.38.5.1 10.38.5.1.1 10.38.5.1.2 10.38.5.1.3 10.38.5.2 10.38.6 10.39 10.39.1 10.39.2 10.39.3 10.39.3.1 10.39.3.2 10.39.4 10.39.4.1 10.39.4.2 10.39.4.3 10.39.4.4 10.39.4.5 10.39.5 10.39.6 10.39.7 10.39.8 10.40 10.40.1 10.40.2 10.40.2.1

General Flanges Welded Girders Riveted or Bolted Girders Thickness of Web Plates Girders Not Stiffened Longitudinally Girders Stiffened Longitudinally Transverse Intermediate Stiffeners Longitudinal Stiffeners Bearing Stiffeners Welded Girders Riveted or Bolted Girders TRUSSES Perforated Cover Plates and Lacing Bars Compression Members—Thickness of Metal COMBINED STRESSES SOLID RIB ARCHES Moment Amplification and Allowable Stress Web Plates Flange Plates COMPOSITE GIRDERS General Shear Connectors Effective Flange Width Stresses Shear Horizontal Shear Fatigue Ultimate Strength Additional Connectors to Develop Slab Stresses Vertical Shear Deflection COMPOSITE BOX GIRDERS General Lateral Distribution of Loads for Bending Moment Design of Web Plates Vertical Shear Secondary Bending Stresses Design of Bottom Flange Plates Tension Flanges Compression Flanges Unstiffened Compression Flanges Stiffened Longitudinally Compression Flanges Stiffened Longitudinally and Transversely Compression Flange Stiffeners, General Design of Flange to Web Welds Diaphragms Lateral Bracing Access and Drainage HYBRID GIRDERS General Allowable Stresses Bending ...

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256 256 256 257 257 257 258 258 260 260 260 261 261 261 261 263 263 263 264 265 265 265 265 266 266 266 266 266 267 268 268 268 268 268 269 269 269 269 269 269 269 272 .272 273 273 273 273 274 274 274 274 274

xxxii

CONTENTS

Division I

10.40.2.2 Shear 10.40.2.3 Fatigue 10.40.3 Plate Thickness Requirements 10.40.4 Bearing Stiffener Requirements 10.41 ORTHOTROPIC-DECK SUPERSTRUCTURES 10.41.1 General 10.41.2 Wheel Load Contact Area 10.41.3 Effective Width of Deck Plate 10.4 1.3.1 Ribs and Beams 10.4 1.3.2 Girders 10.41.4 Allowable Stresses 10.41.4.1 Local Bending Stresses in Deck Plate 10.41.4.2 Bending Stresses in Longitudinal Ribs 10.41.4.3 Bending Stresses in Transverse Beams 10.41.4.4 Intersections of Ribs, Beams, and Girders 10.41.4.5 Thickness of Plate Elements 10.4 1.4.5.1 Longitudinal Ribs and Deck Plate 10.4 1.4.5.2 Girders and Transverse Beams 10.41.4.6 Maximum Slenderness of Longitudinal Ribs 10.41.4.7 Diaphragms 10.41.4.8 Stiffness Requirements 10.41.4.8.1 Deflections 10.41.4.8.2 Vibrations 10.41.4.9 Wearing Surface 10.41.4.10 Closed Ribs

275 275 275 275 275 275 275

275 275 276 276 276 276 276 276 276 276 276 276 277 277 277 277 277 277

PART D—STRENGTH DESIGN METHOD LOAD FACTOR DESIGN 10.42 10.43 10.44 10.45 10.46 10.47 10.48 10.48.1 10.48.2 10.48.3 10.48.4 10.48.5 10.48.6 10.48.7 10.48.8 10.49 10.49.1 10.49.2 10.49.3 10.49.4 10.49.5 10.50 10.50. I 10.50.1.1

SCOPE LOADS DESIGN THEORY ASSUMPTIONS DESIGN STRESS FOR STRUCTURAL STEEL MAXIMUM DESIGN LOADS SYMMETRICAL BEAMS AND GIRDERS Compact Sections Braced Non-Compact Sections Transitions Unbraced Sections Transversely Stiffened Girders Longitudinally Stiffened Girders Bearing Stiffeners Shear UNSYMMETRICAL BEAMS AND GIRDERS General Unsymmetrical Sections with Transverse Stiffeners Longitudinally Stiffened Unsymmetrical Sections Unsymmetrical Braced Non-Compact Sections Unbraced Unsymmetrical Sections COMPOSITE BEAMS AND GIRDERS Positive Moment Sections of Composite Beams and Girders Compact Sections .

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277 277 277 278 278 278 278 278 279 280 280 281 281 282 282 283 283 283 283 283 283 283 284 284

Division I

CONTENTS 10.50.1.2 10.50.2 10.50.2.1 10.50.2.2 10.51 10.51.1 10.51.2 10.51.3 10.51.4 10.5 1.5 10.5 1.6 10.52 10.52.1 10.52.2 10.52.3 10.53 10.53.1 10.53.1.1 10.53.1.2 10.53.1.3 10.53.1.4 10.53.2 10.54 10.54.1 10.54.1.1 10.54.1.2 10.54.2 10.54.2.1 10.54.2.2 10.55 10.55.1 10.55.2 10.55.3 10.56 10.56. 1 10.56.1.1 10.56.1.2 10.56.1.3 10.56.1.4 10.56.2 10.56.3 10.57 10.57.1 10.57.2 10.57.3 10.58 10.58.1 10.58.2 10.58.2.1 10.58.2.2 10.58.3 10.59 10.60

xxxiii

Non-Compact Sections Negative Moment Section of Composite Beams and Girders Compact Sections Non-Compact Sections COMPOSITE BOX GIRDERS Maximum Strength. Lateral Distribution Web Plates Tension Flanges Compression Flanges Diaphragms SHEAR CONNECTORS General Design of Connectors Maximum Spacing HYBRID GIRDERS Non-Composite Hybrid Girders Compact Sections Braced Non-Compact Sections Unbraced Non-Compact Sections Transversely Stiffened Girders Composite Hybrid Girders COMPRESSION MEMBERS Axial Loading Maximum Capacity Effective Length Combined Axial Load and Bending Maximum Capacity Equivalent Moment Factor C SOLID RIB ARCHES. Moment Amplification and Allowable Stresses Web Plates Flange Plates SPLICES, CONNECTIONS, AND DETAILS Connectors General Welds BoltsandRivets Slip-Critical Joints Bolts Subjected to Prying Action by Connected Parts Rigid Connections OVERLOAD Non-Composite Beams and Girders Composite Beams and Girders Slip-Critical Joints FATIGUE General Composite Construction Slab Reinforcement Shear Connectors Hybrid Beams and Girders DEFLECTION ORTHOTROPIC SUPERSTRUCTURES .

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286 286 286 286 286 287 287 287 287 287 288 288 288 288 288 288 289 289 289 289 289 289 289 289 289 290 290 290 290 291 291 291 291 291 291 291 291 291 292 292 292 293 293 293 294 295 295 295 295 295 295 295 295

xxxiv

CONTENTS

Division I

SECTION 11—ALUMINUM DESIGN 11.1 11.2 11.3 11.4 11.5

GENERAL BRIDGES SOIL-METAL PLATE INTERACTION SYSTEMS STRUCTURAL SUPPORTS FOR HIGHWAY SIGNS, LUMINAIRES, AND TRAFFIC SIGNALS BRIDGE RAILING

297 297 297 297 297

SECTION 12-SOIL-CORRUGATED METAL STRUCTURE INTERACTION SYSTEMS 12.1 12.1.1 12.1.2 12.1.3 12.1.4 12.1.5 12.1.6 12.1.6.1 12.1.6.2 12.1.6.3 12.1.7 12.1.8 12.1.9 12.1.10 12.2 12.2.1 12.2.2 12.2.3 12.2.4 12.3 12.3.1 12.3.2 12.3.3 12.3.4 12.4 12.4.1 12.4.1.2 12.4.1.3 12.4.1.4 12.4.1.5 12.4.2 12.4.3 12.4.3.1 12.4.3.2 12.4.4 12.4.5 12.5 12.5.1 12.5.2

GENERAL Scope Notations Loads Design Materials Soil Design Soil Parameters Pipe Arch Design Arch Design Abrasive or Corrosive Conditions Minimum Spacing End Treatment Construction and Installation SERVICE LOAD DESIGN WallArea Buckling Seam Strength Handling and Installation Strength LOAD FACTOR DESIGN WallArea Buckling Seam Strength Handling and Installation Strength CORRUGATED METAL PIPE General.. Service Load Design—safety factor, SF Load Factor Design—capacity modification factor, ~ Flexibility Factor Minimum Cover Seam Strength Section Properties Steel Conduits Aluminum Conduits Chemical and Mechanical Requirements Smooth-Lined Pipe SPIRAL RIB METAL PIPE General Soil Design ....

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299 299 299 299 300 300 300 300 300 300 301 301 301 301 301 301 301 301 301 302 301 302 302 302 302 302 302 302 303 303 303 304 304 304 305 305 305 305 305

Division I

CONTENTS 12.5.2.3 12.5.2.4 12.5.2.5 12.5.3 12.5.3.2 12.5.3.3 12.5.4 12.5.4.1 12.5.4.2 12.5.5 12.5.5.1 12.5.5.2 12.6 12.6.1 12.6.1.2 12.6.1.3 12.6.1.4 12.6.1.5 12.6.2 12.6.3 12.6.3.1 12.6.3.2 12.6.4 12.6.4.1 12.6.4.2 12.6.5 12.7 12.7.1 12.7.2 12.7.2.1 12.7.2.2 12.7.2.3 12.7.2.4 12.7.3 12.7.4 12.7.5 12.8 12.8.1 12.8.1.1 12.8.2 12.8.3 12.8.4 12.8.4.1 12.8.4.2 12.8.4.3 12.8.4.4 12.8.5

Pipe-Arch Design Special Conditions Construction and Installation Design Flexibility Factor Minimum Cover Section Properties Steel Conduits Aluminum Conduits Chemical and Mechanical Requirements Steel Spiral Rib Pipe and Pipe-Arch Requirements— AASHTOM218 Aluminum Spiral Rib Pipe and Pipe-Arch Requirements— AASHTO M 197 STRUCTURAL PLATE PIPE STRUCTURES General Service Load Design—safety factor, SF Load Factor Design—capacity modification factor, ~ Flexibility Factor Minimum Cover Seam Strength Section Properties Steel Conduits Aluminum Conduits Chemical and Mechanical Properties Aluminum Structural Plate Pipe, Pipe-Arch, and Arch Material Requirements—AASHTO M 219, Alloy 5052 Steel Structural Plate Pipe, Pipe-Arch, and Arch Material Requirements—AASHTO M 167 Structural Plate Arches LONG-SPAN STRUCTURAL PLATE STRUCTURES General Design General Acceptable Special Features Design for Deflection Soil Design Structural Plate Shapes End Treatment Multiple Structures STRUCTURAL PLATE BOX CULVERTS General Scope Structural Standards Structure Backfill Design Analytical Basis for Design Load Factor Method Plastic Moment Requirements Footing Reactions Manufacturing and Installation .

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xxxv 305 305 305 305 306 306 306 306 306 306 306 306 307 307 307 307 307 307 307 307 307 307 308 308 308 308 308 308 308 308 309 309 309 310 310 310 310 310 311 311 311 311 311 311 311 313 313

xxxvi

CONTENTS

Division I

SECTION 13-WOOD STRUCTURES 13.1 13.1.1 13.1.2 13.1.3 13.1.4 13.2 13.2.1 13.2.1.1 13.2.1.2 13.2.2 13.2.2.1 13.2.2.2 13.2.3 13.2.3.1 13.2.3.2 13.2.3.3 13.2.3.4 13.2.4 13.3 13.3.1 13.3.2 13.3.3 13.3.4 13.4 13.5 13.5.1 13.5.2 13.5.2.2 13.5.3 13.5.4 13.5.5 13.5.5.1 13.5.5.2 13.5.5.3 13.6 13.6.1 13.6.2 13.6.3 13.6.4 13.6.4.1 13.6.4.2 13.6.4.3 13.6.4.4 13.6.4.5 13.6.5 13.6.5.1 13.6.5.2 13.6.5.3 13.6.6 13.6.6.1 13.6.6.2

GENERAL AND NOTATIONS General Net Section Impact Notations MATERIALS SawnLumber General Dimensions Glued Laminated Timber General Dimensions Structural Composite Lumber General Laminated Veneer Lumber Parallel Strand Lumber Dimensions Piles PRESERVATIVE TREATMENT Requirement for Treatment Treatment Chemicals FieldTreating Fire Retardant Treatments DEFLECTION DESIGN VALUES General Tabulated Values for Sawn Lumber Stress Grades in Flexure Tabulated Values for Glued Laminated Timber Tabulated Values for Structural Composite Lumber Adjustments to Tabulated Design Values Wet Service Factor, CM Load Duration Factor, C~ Adjustment for Preservative Treatment BENDING MEMBERS General Notching Modulus of Elasticity Bending Allowable Stress Size Factor, CF Volume Factor, Cv Beam Stability Factor, CL Form Factor, Cf Shear Parallel to Grain General Actual Stress Allowable Stress Compression Perpendicular to Grain General Allowable Stress .

.

315 315 315 315 315 316 316 316 316 316 316 316 317 317 317 317 317 317 317 317 317 317 317 317 318 318 318 318 318 318 318 318 327 327 327 327 335 335 335 335 335 336 336 337 337 337 337 337 338 338 338

Division I

CONTENTS 13.6.6.3 13.6.7 13.7 13.7.1 13.7.2 13 7 3 13.7.3.1 13.7.3.2 13.7.3.3 13.7.3.4 13.7.3.5 13.7.4 13.8 13.8.1 13.8.2 13.9 13.9.1 13.9.2 13.9.3 13.9.4

Bearing Area Factor, Cb Bearing on Inclined Surfaces COMPRESSION MEMBERS General Eccentric Loading or Combined Stresses Compression Net Section Allowable Stress Column Stability Factor, C~ Tapered Columns Round Columns Bearing Parallel to Grain TENSION MEMBERS Tension Parallel to Grain Tension Perpendicular to Grain MECHANICAL CONNECTIONS General Corrosion Protection Fasteners Washers ..

xxxvii 338 338 38 338 339 39 339 339 339 340 340 340 340 340 341 341 341 341 341 341

SECTION 14—ELASTOMERIC BEARINGS 14.1 14.2 14.3 14.4 14.4.1 14.4.1.1 14.4.1.2 14.4.1.3 14.4.1.4 14.4.1.5 14.4.1.6 14.4.2 14.4.2.1 14.4.2.2 14.4.2.3 14.4.2.4 14.4.2.5 14.4.2.6 145 14.6 14.6.1 14.6.2 14.7 14.8

GENERAL DEFINITIONS MATERIAL PROPERTIES BEARING DESIGN METHODS Method A—Design Procedure for Steel Reinforced, Fabric Reinforced or Plain Bearings Compressive Stress Compressive Deflection Shear Rotation Stability Reinforcement Method B—Optional Design Procedure for Steel Reinforced Bearings Compressive Stress Compressive Deflection Shear Rotation and Combined Compression and Rotation Stability Reinforcement ANCHORAGE DESIGN FORCES FOR SUPPORTING STRUCTURE Shear Force Moment STIFFENERS FOR STEEL BEAMS AND GIRDERS PROVISIONS FOR INSTALLATION EFFECTS .

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343 343 344 344 344 344 345 345 345 345

346 346 346 346 347 347 347 347 347 348 348 348 348 348

xxxviti

CONTENTS

Division I

SECTION 15—TFE BEARING SURFACE 15.1 15.2

GENERAL DESIGN .

349 349

.

SECTION 16-STEEL TUNNEL LINER PLATES 16.1 16.1.1 16.1.2 16.2 16.3 16.3.1 16.3.2 16.3.3 16.3.4 16.3.5 164 16.4.1 16.4.2 16.4.3 16.5 16.6 16.7 16.8

GENERAL AND NOTATIONS General Notations LOADS DESIGN Criteria Joint Strength Minimum Stiffness for Installation Critical Buckling of Liner Plate Wall Deflection or Flattening CHEMICAL AND MECHANICAL REQUIREMENTS Chemical Composition Minimum Mechanical Properties of Flat Pipe Before Cold Forming Dimensions and Tolerances SECTION PROPERTIES COATINGS BOLTS SAFETY FACTORS .

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.

351 351 351 351 352 352 352 353 353 353 354 354 354 354 94 354 354 354

SECTION 17—SOIL-REINFORCED CONCRETE STRUCTURE INTERACTION SYSTEMS 17.1 17.1.1 17.1.2 17.1.3 17.1.4 17.1.5 17.1.6 17.1 .7 17.1.8 17.1.9 17.2 17.3 17.4 17.4.1 17.4.2 17.4.2.1 17.4.2.2 17.4.2.3 17.4.3 17.4.3.1 17.4.3.2 17.4.4

GENERAL Scope Notations Loads Design Materials Soil Abrasive or Corrosive Conditions End Structures Construction and Installation SERVICE LOAD DESIGN LOAD FACTOR DESIGN. REINFORCED CONCRETE PIPE Application Materials Concrete Reinforcement Concrete Cover for Reinforcement Intallations Standard Installations Soils Design .

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355 355 355 356 357 357 357 357 357 357 357 357 357 357 357 357 357 357 358 358 358 358

Division I

CONTENTS

xxxix

17.4.4.1 17.4.4.2 17.4.4.2.1 17.4.4.2. 1.1 17.4.4.2.1.2 17.4.4.2.2 17.4.4.2.3 17.4.4.3 17.4.4.4 17.4.5

General Requirements Loads Earth Loads and Pressure Distribution Standard Installations Nonstandard Installations Pipe Fluid Weight Live Loads Minimun Fill Design Methods Indirect Design Method Based on Pipe Strength and Load-Carrying Capacity 17.4.5.1 Loads 17.4.5.2 Bedding Factor 17.4.5.2.1 Earth Load Bedding Factor for Circular Pipe 17.4.5.2.2 Earth Load Bedding Factor for Arch and Elliptical Pipe 17.4.5.2.3 Live Load Bedding Factor 17.4.5.2.4 Intermediate Trench Widths 17.4.6 Direct Design Method Based on Pressure Distribution 17.4.6.1 Loads 17.4.6.2 Strength-Reduction Factors 17.4.6.3 Process and Material Factors 17.4.6.4 Reinforcement 17.4.6.4.1 Reinforcement for Flexural Strength 17.4.6.4.2 Minimum Reinforcement 17.4.6.4.3 Maximum Flexural Reinforcement Without Stirrups 17.4.6.4.3.1 Limited by Radial Tension 17.4.6.4.3.2 Limited by Concrete Compression 17.4.6.4.4 Crack Width Control 17.4.6.4.5 Shear Strength 17.4.6.4.6 Radial Stirrups 17.4.6.4.6.1 Radial Tension Stirrups 17.4.6.4.6.2 Shear Stirrups 17.4.6.4.6.3 Stirrup Reinforcement Anchorage 17.4.6.4.6.3.1 Radial Tension Stirrup Anchorage 17.4.6.4.6.3.2 Shear Stirrup Anchorage 17.4.6.4.6.3.3 Stirrup Embedment 17.4.6.4.6.3.4 Other Provisions 17.5 REINFORCED CONCRETE ARCH, CAST-IN-PLACE 17.5.1 Application 17.5.2 Materials 17.5.2.1 Concrete 17.5.2.2 Reinforcement 17.5.3 Design 17.5.3.1 General Requirements 17.5.3.2 Minimum Cover 17.5.3.3 Strength-Reduction Factors 17.5.3.4 Splices of Reinforcement 17.5.3.5 Footing Design 17.6 REINFORCED CONCRETE BOX, CAST-IN-PLACE 17.6.1 Application.. 17.6.2 Materials 17.6.2.1 Concrete 17.6.2.2 Reinforcement ....

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358 359 359 359 359 360 360 360 360 360 360 363 363 363 363 363 363 363 364 364 364 364 365 365 365 366 366 367 369 369 370 370 370 370 370 370 370 370 370 370 370 370 370 370 370 370 371 371 371 371 371 371

xl

CONTENTS 17.6.3 17.6.4 17.6.4.1 17.6.4.2 17.6.4.2.1 17.6.4.2.2 17.6.4.3 17.6.4.4 17.6.4.5 17.6.4.6 17.6.4.7 17.6.4.8 17.7 17.7.1 17.7.2 17.7.2.1 17.7.2.2 17.7.3 17.7.4 17.7.4.1 17.7.4.2 17.7.4.2.1 17.7.4.2.2 17.7.4.3 17.7.4.4 17.7.4.5 17.7.4.6 17.7.4.7 17.7.4.8 17.8 17.8.1 17.8.2 17.8.2.1 17.8.2.2 17.8.3 17.8.4 17.8.5 17.8.5.1 17.8.5.2 17.8.5.3 17.8.5.4 17.8.5.5 17.8.5.6 17.8.5.7 17.8.5.8 17.8.5.9 17.8.5. 10 17.8.5.11 17.8.5.12

Division I

Concrete Cover for Reinforcement Design General Requirements Modification of Earth Loads for Soil Structure Interaction Embankment Installations Trench Installations Distribution of Concentrated Load Effects to Bottom Slab Distribution of Concentrated Loads in Skewed Culverts Span Length Strength-Reduction Factors Crack Control Minimum Reinforcement REINFORCED CONCRETE BOX, PRECAST Application.. Materials Concrete Reinforcement Concrete Cover for Reinforcement Design General Requirements Modification of Earth Loads for Soil-Structure Interaction Embankment Installations Trench Installations Distribution of Concentrated Load Effects in Sides and Bottoms Distribution of Concentrated Loads in Skewed Culverts Span Length Strength-Reduction Factors Crack Control Minimum Reinforcement PRECAST REINFORCED CONCRETE THREE-SIDED STRUCTURES Application Materials Concrete Reinforcement Concrete Cover for Reinforcement Geometric Properties Design General Requirements Distribution of Concentrated Load Effects in Sides Distribution of Concentrated Loads in Skewed Culverts Shear Transfer in Transverse Joints Between Culvert Sections Span Length Strength-Reduction Factor Crack Control Minimum Reinforcement Deflection Control Footing Design Structure Backfill Scour Protection .

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371 371 371 .371 .371 .371 .371 .371 372 372 372 372 372 372 372 372 372 372 373 373 373 373 373 373 373 .373 373 373 373 374 374 374 374 374 374 374 374 374 .374 374 374 374 374 375 375 375 375 375 375

Division I

CONTENTS

xli

SECTION 18-SOIL-THERMOPLASTIC PIPE INTERACTION SYSTEMS 18.1 GENERAL 18.1.1 Scope 18.1.2 Notations 18.1.3 Loads 18.1.4 Design 18.1.5 Materials 18.1.6 Soil Design 18.1.6.1 Soil Parameters 18.1.7 Abrasive or Corrosive Conditions 18.1.8 Minimum Spacing 18.1.9 EndTreatment 18.1.10 Construction and Installation 18.2 SERVICE LOAD DESIGN 18.2.1 WallArea 18.2.2 Buckling 18.2.3 Handling and Installation Strength 183 LOAD FACTOR DESIGN 18.3.1 Wall Area 18.3.2 Buckling 18.3.3 Handling and Installation Strength 184 PLASTIC PIPE 18.4.1 General 18.4.1.2 Service Load Design—Safety Factor, SF 18.4.1.3 Load Factor Design—Capacity Modification Factor, ~ 18.4.1.4 Flexibility Factor 18.4.1.5 Minimum Cover 18.4.1.6 Maximum Strain 18.4.1.7 Local Buckling 18.4.2 Section Properties 18.4.2.1 PE Corrugated Pipes 18.4.2.2 PE Ribbed Pipes 18.4.2.3 Profile Wall PVC Pipes 18.4.3 Chemical and Mechanical Requirements 18.4.3.1 Polyethylene 18.4.3.1.1 Smooth Wall PE Pipe Requirements 18.4.3. 1.2 Corrugated PE Pipe Requirements 18.4.3.1.3 RibbedPEPipeRequirements 18.4.3.2 Poly (Vinyl Chloride) (PVC) 18.4.3.2.1 Smooth Wall PVC Pipe Requirements 18.4.3.2.2 Ribbed PVC Pipe Requirements

377 377 377 377 377 377 377 377 378 378 378 378 378 78 378 379 379 379 379 379 79 79 380 380 380 380 380 380 380 380 380 380 381 381 381 381 381 381 381 382

SECTION 19—POT BEARINGS 19.1 19.1.1 19.1.2 19 1 3 19.2 19.2.1 19.2.2 19.2.3

GENERAL Fixed Bearings Guided Expansion Bearings Nonguided Expansion Bearings DESIGN Design Parameters Types of Pot-Bearing Design Limitations of Pot Bearings .

383 383 383 383 383 383 384 384

xlii

CONTENTS

Division I-A

SECTION 20—DISC BEARINGS 20.1 20.1.1 20.1.2 20.1.3 20.2 20.2.1

20.2.2

GENERAL Fixed Bearings Guided Expansion Bearings Nonguided Expansion Bearings DESIGN Design Parameters Limitations of Disc Bearings

385 385 385 385 395 385 386

DIVISION I-A SEISMIC DESIGN SECTION 1—INTRODUCTION 1.1 1.2 1.3 1.4 1.5 1.6

PURPOSE AND PHILOSOPHY BACKGROUND BASIC CONCEPTS PROJECT ORGANIZATION QUALITY ASSURANCE REQUIREMENTS FLOWCHARTS

389 389 390 390 390 390

....

SECTION 2-SYMBOLS AND DEFINITIONS 2.1

NOTATIONS

..

395

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SECTION 3-GENERAL REQUIREMENTS 3.1 3.2 3.3 3.4 3.5 3.5.1 3.6 3.6.1 3.6.2 3.7 3.8 3.9 3.10 3.11 3.12

APPLICABILITY OF SPECIFICATIONS ACCELERATION COEFFICIENT. IMPORTANCE CLASSIFICATION SEISMIC PERFORMANCE CATEGORIES SITE EFFECTS Site Coefficient ELASTIC SEISMIC RESPONSE COEFFICIENT Elastic Seismic Response Coefficient for Single Mode Analysis Elastic Seismic Response Coefficient for Multimodal Analysis RESPONSE MODIFICATION FACTORS DETERMINATION OF ELASTIC FORCES AND DISPLACEMENTS COMBINATION OF ORTHOGONAL SEISMIC FORCES MINIMUM SEAT-WIDTH REQUIREMENTS DESIGN REQUIREMENTS FOR SINGLE SPAN BRIDGES REQUIREMENTS FOR TEMPORARY BRIDGES AND STAGED CONSTRUCTION ...

.

...

. . .

...

397 397 399 399 399 399 400 .400 .400 400 400 400 401 401 402

SECTION 4-ANALYSIS REQUIREMENTS 4.1 4.2

GENERAL SELECTION OF ANALYSIS METHOD

403 403

Division I-A

CONTENTS 4.2.1

xliii

Special Requirements for Single-Span Bridges and Bridges in SPC A Special Requirements for Curved Bridges Special Requirements for Critical Bridges UNIFORM LOAD METHOD—PROCEDURE 1 SINGLE MODE SPECTRAL ANALYSIS METHOD— PROCEDURE 2 MULTIMODE SPECTRAL ANALYSIS METHOD— PROCEDURE 3 General Mathematical Model Superstructure Substructure Mode Shapes and Periods Multimode Spectral Analysis Combination of Mode Forces and Displacements TIME HISTORY METHOD—PROCEDURE 4

403 403 404 404

.

4.2.2 4.2.3 4.3 4.4 4.5 4.5.1 4.5.2 4 5 NA) 4.5.2(B) 4.5.3 4.5.4 4.5.5 4.6

404 405 405 405 406 406 406 406 406 406

SECTION 5—DESIGN REQUIREMENTS FOR BRIDGES IN SEISMIC PERFORMANCE CATEGORY A 5.1 5.2

GENERAL DESIGN FORCES FOR SEISMIC PERFORMANCE CATEGORY A DESIGN DISPLACEMENTS FOR SEISMIC PERFORMANCE CATEGORY A FOUNDATION AND ABUTMENT DESIGN REQUIREMENTS FOR SEISMIC PERFORMANCE CATEGORV A STRUCTURAL STEEL DESIGN REQUIREMENTS FOR SEISMIC PERFORMANCE CATEGORY A REINFORCED CONCRETE DESIGN REQUIREMENTS FOR SEISMIC PERFORMANCE CATEGORY A

407 407

.

5.3

407

..

5.4 5.5 5.6

407 408 408

SECTION 6-DESIGN REQUIREMENTS FOR BRIDGES IN SEISMIC PERFORMANCE CATEGORY B 6.1 6.2 6.2.1 6.2.2 6 23 6.3

GENERAL DESIGN FORCES FOR SEISMIC PERFORMANCE CATEGORY B Design Forces for Structural Members and Connections Design Forces for Foundations Design Forces for Abutments and Retaining Walls DESIGN DISPLACEMENTS FOR SEISMIC PERFORMANCE CATEGORY B Minimum Support Length Requirements for Seismic Performance Category B FOUNDATION AND ABUTMENT DESIGN REQUIREMENTS FOR SEISMIC PERFORMANCE CATEGORY B General Foundations Investigation Foundation Design ...

6.4 6.4.1 6.4.2 6.4.2(A 6.4.2(B)

409 409 409 410

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6.3 I

409

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.

.

410

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.410 410 410 410 410 411

xliv

CONTENTS 6.4.2(C) 6.4.3 6.4.3(A) 6.4.3(B) 6.5 6.5.1 6.5.2 6.6 6.6.1 6.6.2 6.6.2(A) 6.6.2(B)

Division I-A

Special Pile Requirements Abutments Free-Standing Abutments Monolithic Abutments STRUCTURAL STEEL DESIGN REQUIREMENTS FOR SEISMIC PERFORMANCE CATEGORY B General P-delta Effects REINFORCED CONCRETE DESIGN REQUIREMENTS FOR SEISMIC PERFORMANCE CATEGORY B General Minimum Transverse Reinforcement Requirements for Seismic Performance Category B Transverse Reinforcement for Confinement Spacing of Transverse Reinforcement for Confinement ...

411 411 411 412 .

. .

412 412 412 412 412 412 412 413

SECTION 7—DESIGN REQUIREMENTS FOR BRIDGES IN SEISMIC PERFORMANCE CATEGORIES C AND D 7.1 7.2 7.2.1 7.2.1(A) 7.2.1(B) 7.2.2 7.2.2(A) 7.2.2(B) 7.2.3 7.2.4 7.2.5 7.2.5(A) 7.2.5(B) 7.2.5(C) 7.2.6 7.2.7 7.3

GENERAL 415 DESIGN FORCES FOR SEISMIC PERFORMANCE CATEGORIES C AND D 415 Modified Design Forces 415 Modified Design Forces for Structural Members and Connections 415 Modified Design Forces for Foundations 415 Forces Resulting from Plastic Hinging in the Columns, Piers, or Bents 416 Single Columns and Piers 416 Bents with Two or More Columns 416 Column and Pile Bent Design Forces 417 Pier Design Forces 417 Connection Design Forces 417 Longitudinal Linkage Forces 417 Hold-Down Devices 417 Column and Pier Connections to Cap Beams and Footings 417 Foundation Design Forces 417 Abutment and Retaining Wall Design Forces 418 DESIGN DISPLACEMENT FOR SEISMIC PERFORMANCE CATEGORIES C AND D 418 Minimum Support Length Requirements for Seismic Performance Categories C and D 418 FOUNDATION AND ABUTMENT DESIGN REQUIREMENTS FOR SEISMIC PERFORMANCE CATEGORIES CANDD 418 General. 418 Foundation Requirements for Seismic Performance Category C 419 Investigation 419 Foundation Design 419 Special Pile Requirements 419 Abutment Requirements for Seismic Performance Category C 420 ....

7.3 I 7.4

7.4.1 7.4.2 7.4.2(A) 7.4.2(B) 7.4.2(C) 7.4.3

...

.

Division II

xlv

CONTENTS 7.4.3(A) 7.4.3(B) 7.4.4 7.4.4(A) 7.4.4(B) 7.4.5 7.5

Free-Standing Abutments 420 Monolithic Abutments 420 Additional Requirements for Foundations for Seismic Performance Category D 420 Investigation 420 Foundation Design 421 Additional Requirements for Abutments for Seismic Performance Category D .421 STRUCTURAL STEEL DESIGN REQUIREMENTS FOR SEISMIC PERFORMANCE CATEGORIES C AND D 421 General 421 P-delta Effects 421 REINFORCED CONCRETE DESIGN REQUIREMENTS FOR SEISMIC PERFORMANCE CATEGORIES CANDD 421 General 421 Column Requirements 421 Vertical Reinforcement 421 Flexural Strength 421 Column Shear and Transverse Reinforcement 422 Transverse Reinforcement for Confinement at Plastic Hinges 422 Spacing of Transverse Reinforcement for Confinement 423 Splices 423 Pier Requirements 423 Column Connections 424 Construction Joints in Piers and Columns 424 .

7.5.1 7.5.2 7.6

7.6.1 7.6.2 7.6.2(A) 7.6.2(B) 7.6.2(C) 7.6.2(D) 7.6.2(E) 7.6.2(F) 7.6.3 7.6.4 7.6.5

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DIVISION II CONSTRUCTION INTRODUCTION

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426

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SECTION I—STRUCTURE EXCAVATION AND BACKFILL 1.1 1.2 1.3 1.4 1.4.1 1.4.2 1.4.2.1 1.4.2.2 1.4.2.3 1.4.2.4 1.4.2.5

1.4.3 1.5 1.5.1 1.5.2

GENERAL.. WORKING DRAWINGS MATERIALS CONSTRUCTION Depth of Footings Foundation Preparation and Control ofWater General Excavations Within Channels Foundations on Rock Other Foundations Approval of Foundation Backfill MEASUREMENT AND PAYMENT Measurement Payment

427 427 427 427 427 428 428 428 428 428 428 428 429 429 429

SECTION 2-REMOVAL OF EXISTING STRUCTURES 2,1 2.2

DESCRIPTION WORKING DRAWINGS ....

431 431

xlvi

CONTENTS 2.3 2.3.1 2.3.2 2.3.3 2.3.4 2.4

Division II

CONSTRUCTION General Salvage Partial Removal of Structures Disposal MEASUREMENT AND PAYMENT

431 431 431 431 432 432

SECTION 3-TEMPORARY WORKS 3.1 3.1.1 3.1.2 3.1.3 3.1.4 3.1.5 3.2 3.2.1 3.2.2 3.2.2.1 3.2.2.2 3.2.2.3 3.2.2.4 3.2.2.5 3.2.3 3.2.3.1 3.2.3.2 3.2.3.3 3.2.3.4 3.2.3.5 3.2.4 3.2.4.1 3.2.4.2 3.2.4.3 3.3 3.3.1 3.3.2 3.3.3 3.4 3.4.1 3.4.2 3.4.3 3.5 3.5.1 3.5.2 3.5.3 3.5.4 3.6

GENERAL Description Working Drawings Design Construction Removal FALSEWORK AND FORMS General. Falsework Design and Construction Loads Foundations Defiections Clearances Construction Formwork Design and Construction General Design Construction Tube Forms Stay-in-Place Forms Removal of Falsework and Forms General Time of Removal Extent of Removal COFFERDAMS AND SHORING General Protection of Concrete Removal TEMPORARY WATER CONTROL SYSTEMS General Drawings Operations TEMPORARY BRIDGES General Detour Bridges Haul Bridges Maintenance MEASUREMENT AND PAYMENT ..

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433 433 433 433 433 433 434 434 434 434 434 434 434 434 435 435 435 435 435 436 436 436 436 436 437 437 437 437 437 437 437 437 437 437 438 438 438 438

SECTION 4-DRIVEN FOUNDATION PILES 4.1 4.2

DESCRIPTION MATERIALS

..

439 439

Division II

CONTENTS 4.2.1 4.2.1.1 4.2.2 4.2.3 4.3 4.3.1 4.3.1.1 4.3.1.2 4.3.1.3 4.3.1.4 4.3.1.5

4.3.1.5.1 4.3.1.6 4.3.2 4.3.2.1 4.3.2.2 4.4 4.4.1 4.4.1.1 4.4.1.1.1 4.4.1.1.2 4.4.1.1.3 4.4.1.1.4 4.4.1.1.5 4.4.1 .1.6 4.4.1.2 4.4.1.2.1 4.4.1.2.2 4.4.1.2.3 4.4.1.2.4 4.4.1.2.5

4.4.1.2.6 4.4.2 4.4.2.1 4.4.2.1.1 4.4.2.1.2 4.4.2.1.3 4.4.2.2 4.4.2.2.1 4.4.2.2.2 4.4.2.2.3 4.4.3 4.4.3.1 4.4.3.2 4.4.4 4.4.4.1 4.4.4.2 4.4.4.3 4.4.4.4 4.4.4.5 4.4.5 4.4.5.1 4.4.5.2

Steel Piles Painting Timber Piles Concrete Piles MANUFACTURE OF PILES Precast Concrete Piles Forms Casting Finish Curing and Protection Prestressing Working Drawings Storage and Handling Cast-in-Place Concrete Piles Inspection of Metal Shells Placing Concrete DRIVING PILES Pile Driving Equipment Hammers General DropHammers AirSteamHammers Diesel Hammers Vibratory Hammers Additional Equipment or Methods Driving Appurtenances Hammer Cushion Pile Drive Head Pile Cushion Leads Followers Jets Preparation for Driving Site Work Excavation Preboring to Facilitate Driving Predrilled Holes in Embankments Preparation of Piling Collars Pointing Pile Shoes and Lugs Driving Driving of Test Piles Accuracy of Driving Determination of Bearing Capacity General Method A—Empirical Pile Formulas Method B—Wave Equation Analysis Method C—Dynamic Load Tests Method D—Static Load Tests Splicing of Piles Steel Piles Concrete Piles

xlvii

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.

439 439 439 439 440 440 440 440 440 440 440 440 440 440 .440 440 441 441 441 441 441 441 441 442 442 442 442 442 442 442 442 443 443 443 443 443 443 443 443 443 443 443 443 444 444 444 444 444 445 445 446 446 446

xlviii

CONTENTS 4.4.5.3 4.4.6 4.4.7 4.4.7.1 4.4.7.2 4.5 4.5.1

4.5.1.1 4.5.1.1.1 4.5.1.1.2 4.5.1.2 4.5.1.3 4.5.2

Division II

Timber Piles Defective Piles Pile Cut-Off General Timber Piles MEASUREMENT AND PAYMENT Method of Measurement Timber, Steel, and Concrete Piles Piles Furnished Piles Driven Pile Splices, Pile Shoes, and Pile Lugs LoadTests Basis of Payment .

446 446 446 446 446 447 447 447 447 447 447 447 447

.

SECTION 5—DRILLED PILES AND SHAFTS 5.1 5.2 5.3 5.3.1 5.3.2 5.3.3 5.4 5.4.1 5.4.2 5.4.3 5.4.4 5.4.5 5.4.6 5.4.7 5.4.8 5.4.9 5.4.10 5.4.11 5.4.12 5.4.13 5.4.14 5.4.15 5.4.16 5.4.17 5.5 5.6 5.6.1 5.6.1.1 5.6.1.2 5.6.1.3 5.6.1.4 5.6.1.5 5.6.1.6 5.6.1.7 5.6.2 5.6.2.1

DESCRIPTION WORKING DRAWINGS MATERIALS Concrete Reinforcing Steel Casings CONSTRUCTION Protection of Existing Structures Construction Sequence General Methods and Equipment Dry Construction Method Wet Construction Method Temporary Casing Construction Method Permanent Casing Construction Method Alternative Construction Methods Excavations Casings Slurry Excavation Inspection Reinforcing Steel Cage Construction and Placement Concrete Placement, Curing, and Protection Test Shafts and Bells Construction Tolerances Integrity Testing DRILLED SHAFT LOAD TESTS MEASUREMENT AND PAYMENT Measurement Drilled Shaft Bell Footings Test Shafts Test Bells Exploration Permanent Casing LoadTests Payment Drilled Shaft .

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.

449 449 449 449 449 449 449 449 449 450 450 450 450 450 450 451 451 451 451 452 452 452 452 453 453 453 453 453 453 453 454 454 454 454 454 454

Division II

CONTENTS 5.6.2.2 5.6.2.3 5.6.2.4 5.6.2.5 5.6.2.6 5.6.2.7

Bell Footings Test Shafts Test Bells Exploration Holes Permanent Casing Load Tests

xlix 454 454 454 454 454 454

SECTION 6-GROUND ANCHORS 6.1 6.2 6.3 6.3.1 6.3.2 6.3.3 6.3.4 6.3.5 6.4 6.4.1 6.4.1.1 6.4.1.2 6.4.2 6.4.3 6.4.4 6.5 6.5.1 6.5.2 6.5.3 6.5.4 6.5.5 6.5.5.1 6.5.5.2 6.5.5.3 6.5.5.4

6.5.5.5 6.5.5.6 6.6

DESCRIPTION WORKING DRAWINGS MATERIALS. Prestressing Steel Grout Steel Elements Corrosion Protection Elements Miscellaneous Elements FABRICATION Bond Length and Tendon Bond Length Grout Protected Ground Anchor Tendon Encapsulation Protected Ground Anchor Tendon Unbonded Length Anchorage and Trumpet Tendon Storage and Handling INSTALLATION Drilling Tendon Insertion Grouting Trumpet and Anchorage Testing and Stressing Testing Equipment Peformance Test ProofTest Creep Test Ground Anchor Load Test Acceptance Criteria Lock Off MEASUREMENT AND PAYMENT .

455 455 455 455 455 456 456 456 456 456 456 457 457 457 457 457 457 458 458 458 458 458 459 459 460 460 461 461

SECTION 7—EARTH RETAINING SYSTEMS 7.1 7.2 7.3 7.3.1 7.3.1.1 7.3.1.2 7.3.1.3 7.3.2 7.3.3 7.3.4 7.3.5 7.3.5.1

DESCRIPTION WORKING DRAWINGS MATERIALS Concrete Cast-in-Place Pneumatically Applied Mortar Precast Elements Reinforcing Steel Structural Steel Timber Drainage Elements Pipe and Perforated Pipe .

.

463 463 463 463 463 463 463 463 464 464 464

CONTENTS 7.3.5.2

7.3.5.3 7.3.5.4 7.3.6 7.3.6.1 7.3.6.2 7.3.6.3 7.4 7.4.1 7.4.2 7.4.3 7.5 7.5.1 7.5.2 7.5.3 7.5.4 7.6 7.6.1 7.6.2 7.6.2.1 7.6.2.2 7.6.2.3 7.6.2.3.1 7.6.2.3.2 7.6.2.3.3 7.6.2.3.4 7.6.2.3.5 7.6.2.3.6 7.6.3 7.6.3.1 7.6.3.2 7.6.3.3 7.6.3.4 7.6.3.5 7.6.4 7.6.4.1 7.6.4.2 7.6.4.3 7.7

Filter Fabric Permeable Material Geocomposite Drainage Systems Structure Backfill Material General Crib and Cellular Walls Mechanically Stabilized Earth Walls EARTHWORK Structure Excavation Foundation Treatment Structure Backfill DRAINAGE Concrete Gutters Weep Holes Drainage Blankets Geocomposite Drainage Systems CONSTRUCTION Concrete and Masonry Gravity Walls, Reinforced Concrete Retaining Walls Sheet Pile and Soldier Pile Walls Sheet Pile Walls Soldier Pile Walls Anchored Sheet Pile and Soldier Pile Walls General Wales Concrete Anchor Systems Tie-rods Ground Anchors Earthwork Crib Walls and Cellular Walls Foundation Crib Members Concrete Monolithic Cell Members Member Placement Backfilling Mechanically Stabilized Earth Walls Facing Soil Reinforcement Construction MEASUREMENT AND PAYMENT

Division II 464 464 464 464 464 464 464 464 464 464 465 465 465 465 465 465 465 466 466 466 466 467 467 467 467 467 467 467 467 468 468 468 468 468 468 468 469 469 469

SECTION 8-CONCRETE STRUCTURES 8.1 8.1.1 8.1.2 8.1.3 8.2 8.2.1 8.2.2 8.2.3 8.3 8.3.1

GENERAL Description Related Work Construction Methods CLASSES OF CONCRETE General Normal Weight Concrete Lightweight Concrete MATERIALS Cements .

471 471 471 471 471 471 471 471 471 471

Division II

CONTENTS 8.3.2 8.3.3 8.3.4 8.3.5 8.3.6 8.3.7 8.3.8 8.4 8.4.1 8.4.1.1 8.4.1.2 8.4.1.3 8.4.2 8.4.3 8.4.4 8.4.5 8.5 8.5.1 8.5.2 8.5.3 8.5.4 8.5.4.1 8.5.4.2 8.5.5 8.5.6 8.5.7 8.5.7.1 8.5.7.2 8.5.7.3 8.5.7.4 8.5.7.5 8.6 8.6.1 8.6.2 8.6.3 8.6.4 8.6.4.1 8.6.4.2 8.6.4.3 8.6.5 8.6.6 8.6.7 8.7 8.7.1 8.7.2 8.7.2.1 8.7.2.2 8.7.2.3 8.7.2.4 8.7.2.5 8.7.3 8.7.3.1

Water Fine Aggregate Coarse Aggregate Lightweight Aggregate Air-Entraining and Chemical Admixtures Mineral Admixtures Steel PROPORTIONING OF CONCRETE Mix Design Responsibility and Criteria TrialBatchTests Approval Water Content Cement Content Mineral Admixtures Air-Entraining and Chemical Admixtures MANUFACTURE OF CONCRETE Storage of Aggregates Storage of Cement Measurement of Materials Batching and Mixing Concrete Batching Mixing Delivery Sampling and Testing Evaluation of Concrete Strength Tests For Controlling Construction Operations For Acceptance of Concrete For Control of Mix Design Steam and Radiant Heat-Cured Concrete PROTECTION OF CONCRETE FROM ENVIRONMENTAL CONDITIONS General Rain Protection Hot Weather Protection Cold Weather Protection Protection During Cure Mixing and Placing Heating of Mix Special Requirements for Bridge Decks Concrete Exposed to Salt Water Concrete Exposed to Sulfate Soils or Water HANDLING AND PLACING CONCRETE General Sequence of Placement Vertical Members Superstructures Arches Box Culverts Precast Elements Placing Methods General .

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...

.

472 472 472 472 472 473 473 473 473 473 473 473 473 474 474 474 474 474 474 475 475 475 475 475 475 476 476 476 476 476 476 477 477 477 477 477 477 477 477 478 478 478 478 478 478 478 479 479 479 479 479 479

lii

CONTENTS 8.7.3.2 Equipment 8.7.4 Consolidation 8.7.5 Underwater Placement 8.7.5.1 General 8.7.5.2 Equipment 8.7.5.3 Cleanup 8.8 CONSTRUCTION JOINTS 8.8.1 General 8.8.2 Bonding 8.8.3 Bonding and Doweling to Existing Structures 8.8.4 Forms at Construction Joints 8.9 EXPANSION AND CONTRACTION JOINTS 8.9.1 General 8.9.2 Materials 8.9.2.1 Premolded Expansion Joint Fillers 8.9.2.2 Polystyrene Board Fillers 8.9.2.3 Contraction Joint Material 8.9.2.4 Pourable Joint Sealants 8.9.2.5 Metal Armor 8.9.2.6 Waterstops 8.9.2.6.1 Rubber Waterstops 8.9.2.6.2 Polyvinylchloride Waterstops 8.9.2.6.3 Copper Waterstops 8.9.2.6.4 Testing of Waterstop Material 8.9.3 Installation 8.9.3.1 Open Joints 8.9.3.2 Filled Joints 8.9.3.3 Sealed Joints 8.9.3.4 Waterstops 8.9.3.5 Expansion Joint ArmorAssemblies 8.10 FINISHING PLASTIC CONCRETE 8.10.1 General 8.10.2 Roadway Surface Finish 8.10.2.1 Striking Off and Floating 8.10.2.2 Straightedging 8. 10.2.3 Texturing 8. 10.2.3.1 Dragged 8. 10.2.3.2 Broomed 8.10.2.3.3 Tined 8.10.2.4 Surface Testing and Correction 8.10.3 Pedestrian Walkway Surface Finish 8.10.4 Troweled and Brushed Finish 8.10.5 Surface Under Bearings 8.11 CURING CONCRETE 8.11.1 General 8.11.2 Materials 8.11.2.1 Water 8.11.2.2 Liquid Membranes 8.11.2.3 Waterproof Sheet Materials 8.11.3 Methods 8.11.3.1 Forms-In-Place Method 8.11.3.2 WaterMethod 8.11.3.3 Liquid Membrane Curing Compound Method .

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Division II 479 480 480 480 480 481 481 481 481 481 481 481 481 482 482 482 482 482 482 482 482 482 483 483 483 483 483 483 483 483 483 483 484 484 484 484 484 485 485 485 485 485 485 485 485 486 486 486 486 486 486 486 486

Division II

liii

CONTENTS 8.11.3.4 Waterproof Cover Method 8.11.3.5 Steam or Radiant Heat Curing Method 8.11.4 Bridge Decks 8.12 FINISHING FORMED CONCRETE SURFACES 8.12.1 General 8.12.2 Class 1—Ordinary Surface Finish 8.12.3 Class 2-Rubbed Finish 8.12.4 Class 3-Tooled Finish 8.12.5 Class 4-Sandblasted Finish 8.12.6 Class 5—Wire Brushed or Scrubbed Finish 8.13 PRECAST CONCRETE MEMBERS... 8.13.1 General 8.13.2 Working Drawings 8.13.3 Materials and Manufacture 8.13.4 Curing 8.13.5 Storage and Handling 8.13.6 Erection 8.13.7 Epoxy Bonding Agents for Precast Segmental Box Girders 8.13.7.1 Materials 8.13.7.1.1 Test 1—Sag Flow of Mixed Epoxy Bonding Agent 8.13.7.1.2 Test 2—Gel Time of Mixed Epoxy Bonding Agent 8.13.7.1.3 Test 3—Open Time of Bonding Agent 8.13.7.1.4 Test 4—Three-Point Tensile Bending Test 8.13.7.1.5 Test 5—Compression Strength of Cured Epoxy Bonding Agent 8.13.7.1.6 Test 6—Temperature Deflection of Epoxy Bonding Agent 8.13.7.1.7 Test 7—Compression and Shear Strength of Cured Epoxy Bonding Agent 8.13.7.2 Mixing and Installation of Epoxy 8.14 MORTAR AND GROUT 8.14.1 General 8.14.2 Materials and Mixing 8.14.3 Placing and Curing 8.15 APPLICATION OF LOADS 8.15.1 General 8.15.2 Earth Loads 8.15.3 Construction Loads 8.15.4 Traffic Loads 8.16 MEASUREMENT AND PAYMENT 8.16.1 Measurement 8.16.2 Payment .

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486 487 487 487 487 487 488 488 488 488 488 488 489 489 489 489 489 490 490 490 490 490 491 491 491 491 492 492 492 492 493 493 493 493 493 493 493 493 494

SECTION 9—REINFORCING STEEL 9.1 9.2 9.2.1 9.2.2 9.2.3 9.3 9.4 9.4.1

DESCRIPTION MATERIAL Uncoated Reinforcing Epoxy-Coated Reinforcing Mill Test Reports BAR LISTS AND BENDING DIAGRAMS FABRICATION. Bending ....

.

495 495 495 495 495 495 495 495

liv

CONTENTS 9.4.2 9.4.3 9.5 9.6 9.6.1 9.6.2 9.6.3 9.6.4 9.6.5 9.6.6 9.7 9.7.1 9.7.2 9.7.3 9.7.4 9.8 9.9 9.10 9.11

Hooks and Bend Dimensions Identification HANDLING, STORING, AND SURFACE CONDITION OF REINFORCEMENT PLACING AND FASTENING General Support Systems Mortar Blocks Wire Supports Adjustments Repair of Epoxy Coating SPLICING OF BARS General Lapped Splices Welded Splices Mechanical Coupler Splices SPLICING OF MESH OR MATS SUBSTITUTIONS MEASUREMENT PAYMENT ...

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.

Division II 496 496 496 496 496 496 496 496 497 497 497 497 497 497 497 497 497 497 498

SECTION 10—PRESTRESSING 10.1 10.1 I 10.1 .2 10.2 10.2.1 10.2.2 10.3 10.3.1 10.3.1.1 10.3.1.2 10.3.1.3 10.3.2 10.3.2.1 10.3.2.2 10.3.2.3 10.3.2.3.7 10.3.2.3.8 10.3.2.3.9 104 .

GENERAL Description Details of Design SUPPLEMENTARY DRAWINGS Working Drawings Composite Placing Drawings MATERIALS Prestressing Steel and Anchorages Strand Wire Bars Post-Tensioning Anchorages and Couplers Bonded Systems Unbonded Systems Special Anchorage Device Acceptance Test Cyclic Loading Test Sustained Loading Test Monotonic Loading Test PLACEMENT OF DUCTS, STEEL, AND ANCHORAGE HARDWARE Placement of Ducts Vents and Drains Placement of Prestressing Steel Placement for Pretensioning Placement for Post-Tensioning Protection of Steel After Installation Placement of Anchorage Hardware IDENTIFICATION AND TESTING Pretensioning Method Tendons .

.

.

10.4.1 10.4.1.1 10.4.2 10.4.2.1 10.4.2.2 10.4.2.2.1 10.4.3 10.5 10.5.1

.

..

499 499 499 499 499 500 500 500 500 500 500 500 500 500 501 501 501 501 502 502 502 502 902 503 503 503 503 504

Division II

lv

CONTENTS 10.5.2 10.5.3 10.6 10.7 10.8 10.8.1 10.8.2 10.8.3 10.8.4 10.9 10.9.1 10.9.2 10.9.3 10.10 10.10.1 10.10.1.1 10.10.1.2 10.10.1.3 10.10.1.4 10.10.2 10.10.3 10.11 10.11.1 10.11.2 10.11.3 10.11.4 10.11.5 10.11.6 10.12 10.12.1 10.12.2

Post-Tensioning Method Tendons Anchorage Assemblies and Couplers PROTECTION OF PRESTRESSING STEEL CORROSION INHIBITOR.. DUCTS Metal Ducts Polyethylene Duct Duct Area Duct Fittings GROUT Portland Cement Water Admixtures TENSIONING. General Tensioning Requirements Concrete Strength Prestressing Equipment Sequence of Stressing Measurement of Stress Pretensioning Method Requirements Post-Tensioning Method Requirements GROUTING General Preparation of Ducts Equipment Mixing of Grout Injection of Grout Temperature Considerations MEASUREMENT AND PAYMENT Measurement Payment

504 504 504 504 504 505 505 505 505 505 505 505 506 506 506 506 506 507 507 507 508 508 508 508 508 508 509 509 509 509 509

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SECTION 11—STEEL STRUCTURES 11.1 11.1.1 11.1.2 11.1.3 11.1.4 11.2 11.2.1 11.2.2 11.2.3 11.3 11.3.1 11.3.1.1 11.3.1.2 11.3.1.3 11.3.1.4 11.3.1.5 11.3.1.6

GENERAL Description Notice of Beginning of Work Inspection Inspector’s Authority WORKING DRAWINGS ShopDrawings Erection Drawings CamberDiagram MATERIALS StructuralSteel General CarbonSteel High-Strength Low-Alloy Structural Steel High-Strength Low-Alloy, Quenched and Tempered Structural Steel Plate High-Yield Strength, Quenched and Tempered Alloy Steel Plate Eyebars

511 511 511 511 511 512 512 512 512 512 512 512 512 512

....

..

512 .512 513

lvi

CONTENTS 11.3.1.7 11.3.2 11.3.2.1 11.3.2.2 11.3.2.3 11.3.2.4 11.3.2.5 11.3.2.6 11.3.3 11.3.3.1 11.3.3.2 11.3.3.3 11.3.3.4 11.3.3.5 11.3.4 11.3.4.1 11.3.4.2 11.3.5 11.3.5.1 11.3.5.2 11.3.6 11.3.6.1 11.3.6.2 11.3.6.3 11.3.7 11.4 11.4.1 11.4.2 11.4.3 11.4.3.1 11.4.3.2 11.4.3.2.1 11.4.3.2.2 11.4.3.2.3 11.4.3.3 11.4.3.3.1 11.4.3.3.2 11.4.3.3.3 11.4.4 11.4.5 11.4.6 11.4.7 11.4.8 11.4.8.1

Structural Tubing High-Strength Fasteners Material IdentifyingMarks Dimensions Galvanized High-Strength Fasteners Alternative Fasteners Load Indicator Devices Welded Stud Shear Connectors Materials Test Methods Finish Certification Check Samples Steel Forgings and Steel Shafting Steel Forgings Cold Finished Carbon Steel Shafting Steel Castings Mild Steel Castings Chromium Alloy-Steel Castings Iron Castings Materials WorkmanshipandFinish Cleaning Galvanizing FABRICATION Identification of Steels During Fabrication Storage of Materials Plates Direction of Rolling Plate Cut Edges EdgePlaning Oxygen Cutting Visual Inspection and Repair of Plate Cut Edges Bent Plates General Cold Bending HotBending FitofStiffeners AbuttingJoints Facing of Bearing Surfaces Straightening Material Bolt Holes Holes for High-Strength Bolts and Unfinished Bolts 11.4.8.1.1 General 11.4.8.1.2 PunchedHoles 11.4.8.1.3 Reamed or Drilled Holes 11.4.8.1.4 Accuracy of Holes 11.4.8.2 Accuracy of Hole Group 11.4.8.2.1 Accuracy Before Reaming 11.4.8.2.2 Accuracy After Reaming 11.4.8.3 Numerically Controlled Drilled Field Connections .

Division II 513 513 513 513 513 514 514 514 514 514 514 514 515 515 515 515 515 515 515 515 515 515 515 515 515 516 516 516 516 516 516 516 516 516 516 516 516 517 517 517 517 517 517 517 517 518 518 518 518 518 518 518

Division II

CONTENTS 11.4.8.4 11.4.8.5 11.4.9 11.4.9.1 11.4.9.2 11.4.9.3 11.4.10 11.4.11 11.4.12 11.4.12.1 11.4.12.2 11.4.12.2.1 11.4.12.2.2 11.4.12.2.3 11.4.12.2.4 11.4.12.2.5 11.4.12.2.6 11.4.12.2.7 11.4.13 11.4.13.1 11.4.13.2 11.4.13.3 11.4.13.4 11.4.14 11.4.15 11.5 11.5.1 11.5.2 11.5.3 11.5.3.1 11.5.3.2 11.5.3.3 11.5.3.4 11.5.4 11.5.5 11.5.5.1 11.5.5.2 11.5.5.3 11.5.6 11.5.6.1 11.5.6.2 11.5.6.3 11.5.6.4 11.5.6.4.1 11.5.6.4.2 11.5.6.4.3 11.5.6.4.4 11.5.6.4.5 11.5.6.4.6 11.5.6.4.7

Holes for Ribbed Bolts, Turned Bolts, or Other Approved Bearing Type Bolts Preparation of Field Connections PinsandRollers General Boring Pin Holes ThreadsforBoltsandPins Eyebars Annealing and Stress Relieving Curved Girders General Heat Curving Rolled Beams and Welded Girders Materials Type of Heating Temperature Position for Heating Sequence of Operations Camber Measurement of Curvature and Camber Orthotropic-Deck Superstructures General FlatnessofPanels Straightness of Longitudinal Stiffeners Subject to Calculated Compressive Stress, Including Orthotropic-Deck Ribs Straightness of Transverse Web Stiffeners and Other Stiffeners Not Subject to Calculated Compressive Stress Full-Sized Tests Marking and Shipping ASSEMBLY Bolting Welded Connections Preassembly of Field Connections General Bolted Connections Check Assembly—Numerically Controlled Drilling Field Welded Connections Match Marking Connections Using Unfinished, Turned, or Ribbed Bolts General Turned Bolts Ribbed Bolts Connections Using High-Strength Bolts General Bolted Parts Surface Conditions Installation General Rotational-Capacity Tests Requirement for Washers Turn-of-Nut Tightening Calibrated Wrench Tightening Installation of Alternate Design Bolts Direct Tension Indicator Tightening .

...

lvii

518 519 519 519 519 519 519 519 520 520 520 520 520 520 520 521 521 521 521 521 521 522 522 522 522 522 522 522 522 522 523 523 523 523 523 523 523 523 524 524 524 524 524 524 525 525 526 527 527 527

Division II

CONTENTS

lviii

Verification 11.5.6.4.7(A) Installation 11.5.6.4.7(B) Lock-Pin and Collar Fasteners 11.5.6.4.8 11.5.6.4.9 Inspection 11.5.7 Welding 11.6 ERECTION 11.6.1 General 11.6.2 Handling and Storing Materials 11.6.3 Bearings and Anchorages 11.6.4 Erection Procedure 11.6.4.1 Conformance to Drawings 11.6.4.2 Erection Stresses 11.6.4.3 Maintaining Alignment and Camber 11.6.5 Field Assembly 11.6.6 Pin Connections 11.6.7 Misfits 11.7 MEASUREMENT AND PAYMENT Method of Measurement 11.7.1 11.7.2 Basis of Payment .

527 528 528 529 529 529 529 529 529 530 530 530 530 530 530 530 530 530 531

SECTION 12-STEEL GRID FLOORING 12.1 12.1.1 12.1.2 12.2 12.2.1 12.2.2 12.2.3 12.2.4 12.3 12.4 12.5 12.6 12.7 12.8 12.9 12.9.1 12.9.2 12.10

GENERAL Description Working Drawings MATERIALS Steel Protective Treatment Concrete Skid Resistance ARRANGEMENT OF SECTIONS PROVISION FOR CAMBER FIELD ASSEMBLY CONNECTION TO SUPPORTS WELDING REPAIRING DAMAGED GALVANIZED COATINGS PLACEMENT OF CONCRETE FILLER Forms Placement MEASUREMENT AND PAYMENT . .

.

533 533 533 533 533 533 533 533 533 534 534 534 534 534 534 534 535 535

SECTION 13-PAINTING 13.1 13.1.1 13.1.2 13.1.3 13.1.4 13.2 13.2.1 13.2.2 13.2.3

GENERAL Description Protection of Public and Property Protection of the Work Color PAINTING METAL STRUCTURES Coating Systems and Paints Weather Conditions Surface Preparation

537 537 537 537 537 537 537 537 538

Division II

CONTENTS 13.2.3.1 13.2.3.2 13.2.3.3 13.2.3.4 13.2.4 13.2.4.1 13.2.5 13.3 13.4 13.4.1 13.4.2 13.4.3 13.4.4 13.4.5 13.4.6 13.5 13.5.1 13.5.2 13.5.3 13.5.4

lix

Blast Cleaning Steam Cleaning Solvent Cleaning Hand Cleaning Application of Paints Application of Zinc-Rich Primers Measurement and Payment PAINTING GALVANIZED SURFACES PAINTING TIMBER General Preparation of Surfaces Paint Application Painting Treated Timber Payment PAINTING CONCRETE Surface Preparation Paint Application Measurement and Payment

538 539 539 539 539 540 540 540 541 541 541 541 541 541 541 541 541 542 542 542

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SECTION 14-STONE MASONRY 14.1 14.1.1 14.1.2 14.2 14.2.1.1 14.2.1.2 14.2.2 14.2.3 14.3 14.3.1 14 3 2 14 3 3 14.3.3.1 14.3.3.2 14.3.3.3 14.3.4 14.3.4.1 14.3.4.2 14.3.4.3 14.3.5 14.4 14.4.1 14.4.2 14.4.3 14.4.3.1 14.4.3.2 14.4.3.3 14.4.4 14.4.5

DESCRIPTION Rubble Masonry Ashlar Masonry MATERIALS Rubble Stone AshlarStone Shipment and Storage of Stone Mortar MANUFACTURE OF STONE FOR MASONRY General Surface Finishes of Stone Rubble Masonry Size Shape Dressing Ashlar Masonry Size Dressing Stretchers Arch Ring Stones CONSTRUCTION Weather Conditions Mixing Mortar Selection and Placing of Stone General Rubble Masonry Ashlar Masonry Beds and Joints Headers ..

...

.

543 543 543 543 543 543 543 543 544 544 544 544 544 544 544 544 544 544 545 545 545 545 545 545 545 545 546 546 546

lx

CONTENTS 14.4.6 14.4.6.1 14.4.6.2 14.4.6.3 14.4.6.4 14.4.7 14.4.8 14.4.8.1 14.4.8.2 14.4.9 14.4.10 14.4.11 14.4.12 14.5

Division II

Cores and Backing General Stone Concrete Leveling Courses Facing for Concrete Copings Stone Concrete Dowels and Cramps Weep Holes Pointing Arches MEASUREMENT AND PAYMENT

546 546 546 546 546 547 547 547 547 547 547 547 548 548

.

SECTION 15—CONCRETE BLOCK AND BRICK MASONRY 15.1 15.2 15.2.1 15.2.2 15.2.3 15.2.4 15.2.5 15.2.6 15.2.6.1 15.2.6.2 15.3 15.3.1 15.3.2 15.3.3 15.3.4 15.3.5 15.4

DESCRIPTION MATERIALS Concrete Block Brick Reinforcing Steel Mortar Grout Sampling and Testing Mortar Grout CONSTRUCTION Weather Conditions Laying Block and Brick Placement of Reinforcement Grouting of Voids Copings, Bridge Seats, and Backwalls MEASUREMENT AND PAYMENT

549 549 549 549 549 549 549 549 549 550 550 550 550 550 550 551 552

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SECTION 16-TIMBER STRUCTURES 16.1 16.1.1 16.2 16.2.1 16.2.2 16.2.3 16.2.4 16.2.5 16.2.6 16.2.6.1 16.2.6.2 16.2.6.3 16.2.6.4 16.3 16.3.1

GENERAL Related Work MATERIALS Lumber and Timber (Solid Sawn or Glued Laminated) Steel Components Castings Hardware Galvanizing Timber Connectors Dimensions Split Ring Connectors Shear-Plate Connectors Spike-Grid Connectors FABRICATION AND CONSTRUCTION Workmanship .

..

553 553 553 553 553 554 554 554 554 554 554 554 554 555 555

Division II

CONTENTS 16.3.2 16.3.3 16.3.3.1 16.3.3.2 16.3.3.3 16.3.3.4 16.3.3.5 16.3.4 16.3.5 16.3.6 16.3.7 16.3.8 16.3.9 16.3.9.1 16.3.9.2 16.3.9.3 16.3.9.4 16.3.9.5 16.3.9.6 16.3. 10 16.3.11 16.3.12 16.3.13 16.3.14 16.3.15 16.3.16 16.4 16.5 16.6

Storage of Material Treated Timber Handling Framing and Boring Cuts and Abrasions Bored Holes Temporary Attachment Installation of Connectors Holes for Bolts, Dowels, Rods, and Lag Screws Bolts and Washers... Countersinking Framing Framed Bents Mud Sills Concrete Pedestals Sills Posts Caps Bracing Stringers.... PlankFloors.. Nail Laminated or Strip Floors Glue Laminated Panel Decks Composite Wood-Concrete Decks Wheel Guards and Railing Trusses PAINTING MEASUREMENT PAYMENT ..

lxi 555 555 555 555 556 556 556 556

556 556 557 557 557 557 557 557 557 557 557 557 558 558 558 558 558 559 559 559 559

SECTION 17—PRESERVATIVE TREATMENT OF WOOD 17.1 17.2 17.2.1 17.2.2 17.2.3 17.3 17.3.1 17.3.2 17.3.3 17.4

GENERAL MATERIALS Wood.. Preservatives and Treatments Coal-Tar Roofing Cement IDENTIFICATION AND INSPECTION Branding and Job Site Inspection Inspection at Treatment Plant Certificate of Compliance MEASUREMENT AND PAYMENT

561 561 561 561 561 561 561 562 562 562

SECTION 18-BEARING DEVICES 18.1 18.1.1 18.1.2 18.1.3 18.1.4 18.2 18.2.1

GENERAL Working Drawings Packaging, Handling, and Storage Manufacture or Fabrication Construction and Installation ELASTOMERIC BEARINGS Scope

563 563 563 563 563 564 564

lxii

CONTENTS 18.2.2 General Requirements 18.2 3 Materials 18.2.3.1 Properties of the Elastomer 18.2.3.2 Steel Laminates 18.2.3.3 Fabric Reinforcement 18.2.3.4 Bond 18.2.4 Fabrication 18.2.5 Fabrication Tolerances 18.2.6 Marking and Certification 18.2.7 Testing 18.2.7.1 Scope 18.2.7.2 Frequency of Testing 18.2.7.3 Ambient-Temperature Tests on the Elastomer 18.2.7.4 Low-Temperature Tests on the Elastomer 18.2.7.5 Visual Inspection of the Finished Bearing 18.2.7.6 Short-Duration Compression Tests on Bearings 18.2.7.7 Long-Duration Compression Tests on Bearings 18.2.7.8 Shear Modulus Tests on Material from Bearings 18.2.8 Installation 18.3 POT AND DISC BEARINGS 18.3.1 General 18.3.2 Working Drawings 18.3.3 Materials 18.3.3.1 Elastomeric Rotational Element 18.3.3.2 Sealant 18.3.3.3 Sealing Rings 18.3.3.4 Steel 18.3.3.5 Stainless Steel 18.3.3.6 Polytetrafluorethylene Sheet and Strip 18.3.3.7 Polyether Urethane Structural Element 18.3.4 Fabrication Details 18.3.5 Sampling and Testing 18.3.5.1 Lot Size 18.3.5.2 Sampling and Testing Requirements 18.3.5.2.1 Testing by Manufacturer 18.3.5.2.2 Testing by the Engineer 18.3.5.3 Performance Characteristics 18.3.5.3.1 Proof Load Test 18.3.53.2 Sliding Coefficient of Friction 18.3.6 Installation 18.4 ROCKER, ROLLER, AND SLIDING BEARINGS 18.4.1 Materials 18.4.2 Fabrication 18.4.3 Installation 18.5 SPHERICAL BEARINGS 18.6 BRONZE OR COPPER-ALLOYED PLATES FOR BEARINGS 18.6.1 Bronze Bearing and Expansion Plates 18.6.2 Rolled Copper-Alloy Bearings and Expansion Plates 18.6.3 Metal Powder Sintered Bearings and Expansion Joints (Oil Impregnated) 18.7 MASONRY, SOLE, AND SHIM PLATES FOR BEARINGS 18.7.1 Materials 18.7.2 Fabrication .

Division II

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564 564 564 564 564 564 564 567 567 567 567 567 568 568 568 568 568 568 569 569 569 569 569 569 569 569 570 570 570 570 570 571 571 571 571 571 572 572 572 572 572 572 572 572 573 .573 573 573 573 973 573 573

Division II

CONTENTS 18.7.3 18.8 18.8.1 18.8.1.1 18.8.1.2 18.8.1.3 18.8.1.4 18.8.1.5 18.8.1.6 18.8.1.7 18.8.1.8 18.8.1.9 18.8.1.10 18.8.1.11 18.8.2 18.8.2.1 18.8.2.1.1 18.8.2.1.2 18.8.2.1.3 18.8.3 18.8.3.1 18.8.3.2 18.8.3.3 18.9 18.9.1 18.9.2 18.9.3 18.10 18.10.1 18.10.2 18.11 18.12

Installation TFE SURFACES FOR BEARINGS Materials General TFE Resin Filler Material Adhesive Material Unfilled TFE Sheet Filled TFE Sheet Fabric Containing TFE Fibers Interlocked Bronze and Filled TFE Structures TFE Metal Composite SurfaceTreatment Stainless Steel Mating Surface Manufacturing Requirements Attachment of TFE Material Bonding Mechanically Fastened Fabric Containing TFE Fibers Testing and Acceptance General Test Specimens Test Method ANCHOR BOLTS Materials Fabrication Installation BEDDING OF MASONRY PLATES General Materials MEASUREMENT PAYMENT ..

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lxiii 573 573 573 573 573 573 573 573 574 574 574 574 574 574 574 574 574 574 574 575 575 575 575 575 575 575 575 575 575 576 576 576

SECTION 19—BRIDGE DECK JOINT SEALS 19.1 19.2 19.3 19.4 19.4.1 19.4.2 19.5 19.5.1 19.5.2 19.5.3 19.6

GENERAL WORKING DRAWINGS MATERIALS MANUFACTURE AND FABRICATION Compression Seal Joints Joint Seal Assemblies INSTALLATION General Compression Seal Joints Joint Seal Assemblies MEASUREMENT AND PAYMENT ..

..

.

577 977 577 577 577 577 577 577 578 578 578

SECTION 20-RAILINGS 20.1 20.1.1

GENERAL Description

579 579

lxiv

CONTENTS 20.1.2 20.1.3 20.1.4 20.2 20.2.1 20.2.1.1 20.2.1.2 20.2.1.3 20.2.1.4 20.2.2 20.2.3 20.3 20.3.1 20.4 20.5 20.6 20.7 20.7.1 20.7.2

Division II

Materials Construction Line and Grade METAL RAILING Materials and Fabrication Steel Railing Aluminum Railing Metal Beam Railing Welding Installation Finish CONCRETE RAILING Materials and Construction TIMBER RAILING STONE AND BRICK RAILINGS TEMPORARY RAILING MEASUREMENT AND PAYMENT Measurement Payment

579 579 579 579 579 579 579 579 579 579 580 580 580 580 580 580 580 580 580

..

SECTION 21—WATERPROOFING 21.1 21.1.1 21.1.2 21.2 21.2.1 21.2.1.1 21.2.1.2 21.2.1.3 21.2.2 21.2.2.1 2 1.2.2.2 21.2.2.3 2 1.2.3 21.2.4 2 1.2.5 21.3 21.4 21.4.1 21.4.1.1 21.4.1.2 2 1.4.1.3 21.4.1.4 21.4.2 21.4.2.1 21.4.2.2 21 4 2 3 21 4 3 2144 21 5

GENERAL Waterproofing Dampproofing MATERIALS Asphalt Membrane Waterproofing System Asphalt Primer Fabric Preformed Membrane Waterproofing Systems Primer Preformed Membrane Sheet Mastic Protective Covers Dampproofing Inspection and Delivery SURFACE PREPARATION APPLICATION Asphalt Membrane Waterproofing General Installation Special Details Damage Patching Preformed Membrane Waterproofing Systems General Installation on Bridge Decks Installaion on Other Surfaces Protective Cover Dampproofing MEASUREMENT AND PAYMENT. .

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581 581 581 581 581 581 581 581 581 581 581 582 582 582 582 582 582 583 583 583 583 583 584 584 584 584 584 585 585

Division II

CONTENTS

lxv

SECTION 22—SLOPE PROTECTION 22.1 22.1.1 22.1.2 22.2

22.3 22.3.1 22.3.2 22.3.3

22.3.4 22.3.5 22.3.6 22.3.7 22.3.8 22.3.9 22.3.10 22.4 22.4.1 22.4.2

22.4.3 22.4.4 22.4.5 22.4.6 22.4.6.1 22.4.6.2 22.4.7 22.4.7.1 22.4.7.2 22.4.8 22.4.9 22.4.10 22.4.10.1 22.4.10.2 22.4.10.3 22.5 22.5.1 22.5.1.1 22.5.1.2 22.5.1.3 22.5.1.4 22.5.1.5 22.5.1.6 22.5.2 22.5.2.1 22.5.2.2 22.5.2.3 22.5.2.4 22.5.2.5 22.5.2.6 22.5.2.7

GENERAL Description Types WORKING DRAWINGS MATERIALS Aggregate Wire-Enclosed Riprap (Gabions) Filter Fabric Grout Sacked Concrete Riprap Portland Cement Concrete Pneumatically Applied Mortar Precast Portland Cement Concrete Blocks and Shapes Reinforcing Steel Geocomposite Drain CONSTRUCTION Preparation of Slopes Bedding Filter Fabric Geocomposite Drain Hand Placing Stones Machine-Placed Stones Dry Placement Underwater Placement Wire-Enclosed Riprap (Gabions) Fabrication Installation Grouted Riprap Sacked Concrete Riprap Concrete Slope Paving General Cast-in-Place Slope Paving Precast Slope Paving MEASUREMENT AND PAYMENT Method of Measurement Stone Riprap and Filter Blanket Sacked Concrete Riprap Wire-Enclosed Riprap (Gabions) Cast-in-Place Concrete Slope Paving Precast Concrete Slope Paving Filter Fabric Payment General Stone Riprap Sacked Concrete Riprap Wire-Enclosed Riprap (Gabions) Cast-in-Place Concrete Slope Paving Precast Concrete Slope Paving Filter Blanket .

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587 587 587 987 987 587 587 587 588 588 588 588 588 588 588 588 588 588 588 589 589 589 589 589 589 589 590 590 590 590 590 991 591 591 591 591 591 991 592 592 592 592 592 592 592 592 592 592 592

lxvi

CONTENTS 22.5.2.8 22.5.2.9

Filter Fabric Geocomposite Drain System

Division II 592 592

SECTION 23—MISCELLANEOUS METAL 23.1 23.2 23.3 23.4 23.5 23.6

DESCRIPTION MATERIALS FABRICATION GALVANIZING MEASUREMENT PAYMENT ....

593 593 593 593 593 593

SECTION 24—PNEUMATICALLY APPLIED MORTAR 24.1 24.2 24.2.1 24.2.2 24.2.3 24.3 24.3.1 24.3.2 24.4 24.4.1 24.4.2 24.4.3 24.5 24.5.1 24.5.2 24.5.2.1 24.5.2.2 24.5.3 24.5.4 24.6

DESCRIPTION MATERIALS Cement, Aggregate, Water, and Admixtures Reinforcing Steel Anchor Bolts or Studs PROPORTIONING AND MIXING Proportioning Mixing SURFACE PREPARATION Earth Forms Concrete or Rock INSTALLATION Placement of Reinforcing Placement of Mortar Weather Limitations Protection of Adjacent Work Finishing Curing and Protecting MEASUREMENT AND PAYMENT

595 595 595 595 595 595 595 595 596 596 596 596 596 596 596 597 597 597 597 597

SECTION 25—STEEL AND CONCRETE TUNNEL LINERS 25.1 25.2 25.3 25.3.1 25.3.2 25.4 25.4.1 25.4.2 25.4.3 25.5 25.6

SCOPE DESCRIPTION MATERIALS AND FABRICATION General Forming and Punching of Steel Liner Plates INSTALLATION Steel Liner Plates Precast Concrete Liner Plates Grouting MEASUREMENT PAYMENT ...

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599 599 599 599 599 600 600 600 600 600 600

Division II

CONTENTS

lxvii

SECTION 26-METAL CULVERTS 26.1 26.1.1 26.2 26.3 26.3.1 26.3.2 26.3.3 26.3.4 26.3.5 26.3.6 26.3.7 26.3.8 26.3.8.1 26.3.8.2 26.3.8.3 26.4 26.4.1 26.4.2 26.4.2.1 26.4.2.2 26.4.2.3 26.4.2.4 26.4.3 26.5 26.5. 1 26.5.2 26.5.3 26.5.4 26.5.4.1 26.5.4.2 26.5.4.3 26.5.4.4 26.5.4.5 26.5.5 26.6 26.7 26.8

GENERAL Description WORKING DRAWINGS MATERIALS Corrugated Metal Pipe Structural Plate NutsandBolts Mixing of Materials Fabrication Welding Protective Coatings Bedding and Backfill Materials General Long-Span Structures Box Culverts ASSEMBLY General Joints Field Joints Joint Types Soil Conditions Joint Properties Assembly of Long-Span Structures INSTALLATION Placing Culverts—General Foundation Bedding Structural Backfill General Arches Long-Span Structures Box Culverts Bracing Arch Substructures and Headwalls CONSTRUCTION PRECAUTIONS MEASUREMENT PAYMENT

601 601 601 601 601 601 601 601 601 602 602 602 602 602 602 602 602 602 603 603 603 603 604 604 604 604 606 607 607 607 607 608 608 608 609 609 609

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SECTION 27—CONCRETE CULVERTS 27.1 27.2 273 27 3 1 27.3.2 27.3.2.1 27.3.2.2 27.3.2.3 27.3.3 27.3.3.1

GENERAL WORKING DRAWINGS MATERIALS Reinforced Concrete Culverts Joint Sealants Cement Mortar Flexible Watertight Gaskets Other Joint Sealant Materials Bedding, Haunch, Lower Side and Backfill or Overfill Material Precast Reinforced Concrete Circular, Arch, and Elliptical Pipe

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611 611 611 611 611 611 611 612 .612 .612

lxviii

CONTENTS

Division II

27.3.3.2 Precast Reinforced Concrete Box Sections 27.4 ASSEMBLY 27.4.1 General 27.4.2 Joints 27.5 INSTALLATION 27.5.1 General 27.5.2 Bedding 27.5.2.1 General 27.5.2.2 Precast Reinforced Concrete Circular Arch and Elliptical Pipe 27.5.2.3 Precast Reinforced Concrete Box Sections 27.5.3 Placing Culvert Sections 27.5.4 Haunch, Lower Side and Backfill or Overfill 27.5.4.1 Precast Reinforced Concrete Circular Arch and Elliptical Pipe 27.5.4.1.1 Haunch Material 27.5.4.1.2 Lower Side Material 27.5.4.1.3 Overfill 27.5 .4.2 Precast Reinforced Concrete Box Sections 27.5.4.2.1 Backfill 27.5.4.3 Placing of Haunch, Lower Side and Backfill or Overfill 27.5.4.4 Cover Over Culvert During Construction 27.6 MEASUREMENT 27.7 PAYMENT

612 612 612 612 612 612 612 612 615 615 615 616 616 616 619 619 619 619 619 620 620 620

.

SECTION 28-WEARING SURFACES 28.1 DESCRIPTION 28.2 LATEX MODIFIED CONCRETE TYPE WEARING SURFACE 28.2.1 General 28.2.2 Materials 28.2.2.1 Portland Cement 28.2.2.2 Aggregate 28.2.2.3 Water 28.2.2.4 Latex Emulsion 28.2.2.5 Latex Modified Concrete 28.2.3 Surface Preparation 28.2.3.1 New Decks 28.2.3.2 Existing Decks 28.2.4 Proportioning and Mixing 28.2.5 Installation 28.2.5.1 Weather Restrictions 28.2.5.2 Equipment 28.2.5.3 Placing and Finishing 28.2.5.3.1 Construction Joints 28.2.5.3.2 Placing 28.2.5.3.3 Finishing 28.2.6 Curing 28.2.7 Acceptance Testing 28.2.8 Measurement and Payment .

.

.

. .

621 .621 621 621 621 621 621 621 622 622 622 622 623 623 623 623 623 624 624 624 624 624 625

SECTION 29—EMBEDMENT ANCHORS 29.1 29.2

DESCRIPTION PREQUALIFICATION

.

627 627

Division II

CONTENTS 29.3 29.4 29.5 29.6 29.7

MATERIALS CONSTRUCTION METHODS INSPECTION AND TESTING MEASUREMENT. PAYMENT. ..

lxix 627 627 627 628 628

APPENDICES: A—Live Load Tables B—Truck Train Loadings C—Columns D—Plastic Section Modulus E—Metric Equivalents and Expressions

629 633 634 38 639

INDEX

671

COMMENTARY—Interim Specifications—Bridges—1996

C-I

Division I DESIGN

Section 1 GENERAL PROVISIONS 1.1

1.3

DESIGN ANALYSIS AND GENERAL STRUCTURAL INTEGRITY FOR BRIDGES

1.3.1 The intent of these Specifications is to produce integrity of design in bridges.

1.1.1

Design Analysis

Structural Integrity

Designs and details for new bridges should address structural integrity by considering the following: (a) The use of continuity and redundancy to provide one or more alternate load paths. (b) Structural members and bearing seat widths that are resistant to damage or instability. (c) External protection systems to minimize the effects of reasonably conceived severe loads.

1.2

General

1.3.1.1 Selecting favorable stream crossings should be considered in the preliminary route determination to minimize construction, maintenance, and replacement costs. Natural stream meanders should be studied and, if necessary, channel changes, river training works, and other construction that would reduce erosion problems and prevent possible loss of the structure should be considered. The foundations of bridges constructed across channels that have been realigned should be designed for possible deepening and widening of the relocated channel due to natural causes. On wide flood plains, the lowering of approach embankments to provide overflow sections that would pass unusual floods over the highway is a means of preventing loss of structures. Where relief bridges are needed to maintain the natural flow distribution and reduce backwater, caution must be exercised in proportioning the size and in locating such structures to avoid undue scour or changes in the course of the main river channel.

When these Specifications provide for empirical formulae, alternate rational analyses, based on theories or tests and accepted by the authority having jurisdiction, will be considered as compliance with these Specifications.

1.1.2

WATERWAYS

1.3.1.2 Usually, bridge waterways are sized to pass a design flood of a magnitude and frequency consistent with the type or class of highway. In the selection of the waterway opening, consideration should be given to the amount of upstream ponding, the passage of ice and debris and possible scour of the bridge foundations. Where floods exceeding the design flood have occurred, or where superfioods would cause extensive damage to adjoining property or the loss of a costly structure, a larger waterway opening may be warranted. Due consideration should be given to any Federal, State, and local requirements.

BRIDGE LOCATIONS

The general location of a bridge is governed by the route of the highway it carries, which, in the case of a new highway, could be one of several routes under consideration. The bridge location should be selected to suit the particular obstacle being crossed. Stream crossings should be located with regard to initial capital cost of bridgeworks and the minimization of total cost including river channel training works and the maintenance measures necessary to reduce erosion. Highway and railroad crossings should provide for possible future works such as road widening.

1.3.1.3 Relief openings, spur-dikes. debris defiectors and channel training works should be used where needed to minimize the effect of adverse flood flow conditions. Where scour is likely to occur, protection against damage from scour should be provided in the design of bridge piers and abutments. Embankment slopes adjacent to structures subject to erosion should be adequately pro3

HIGHWAY BRIDGES

4

tected by rip-rap, flexible mattresses, retards, spur dikes or other appropriate construction. Clearing of brush and trees along embankments in the vicinity of bridge openings should be avoided to prevent high flow velocities and possible scour. Borrow pits should not be located in areas which would increase velocities and the possibility of scour at bridges.

1.3.2

Hydraulic Studies

Hydraulic studies of bridge sites are a necessary part of the preliminary design of a bridge and reports of such studies should include applicable parts of the following outline:

1.3.2.1

Site Data

(a) Maps. stream cross sections, aerial photographs. (b) Complete data on existing bridges, including dates of construction and performance during past floods. (c) Available high water marks with (lates of occurrence. (d) Information on ice, debris, and channel stability. (e) Factors affecting water stages such as high water from other streams, reservoirs, flood control projects. and tides. (f) Geomorphic changcs in channel flow.

1.3.2.2

CULVERT LOCATION, LENGTH, AND WATERWAY OPENINGS

Culvert location, length, and waterway openings should be in accordance with the AASHTO Guide on the Hydraulic Design of Culverts in Highway Drainage Guidelines. 1.5

ROADWAY DRAINAGE

The transverse drainage of the roadway should be provided by a suitable crown in the roadway surface and longitudinal drainage by camber or gradient. Water flowing downgrade in a gutter section should be intercepted and not permitted to run onto the bridge. Short, continuous span bridges, particularly overpasses, may be built without inlets and the water from the bridge roadway carried downslope by open or closed chutes near the end of the bridge structure. Longitudinal drainage on long bridges should be provided by scuppers or inlets which should be of sufficient size and number to drain the gutters adequately. Downspouts, where required, should be made of rigid corrosion-resistant material not less than 4 inches in least dimension and should be provided with cleanouts. The details of deck drains should be such as to prevent the discharge of drainage water against any portion of the structure or on moving traffic below, and to prevent erosion at the outlet of the downspout. Deck drains may be connected to conduits leading to storm water outfalls at ground level. Overhanging portions of concrete decks should be provided with a drip bead or notch.

Hydrologic Analysis

(a) Flood data applicable to estimating floods at site. including both historical floods and maximum floods of record. (b) Flood-frequency curve for site. (c) Distribution of flow and velocities at site for flood discharges to be considered in design of structure. (d) Stage-discharge curve for site.

1.3.2.3

1.4

1.3.1.3

Hydraulic Analysis

(a) Backwater and mean velocities at bridge opening for various trial bridge lengths and selected discharges. (b) Estimated scour depth at piers and abutments of proposed structures. (c) Effect of natural geomorphic stream pattern changes on the proposed structure. (d) Consideration of geomorphic changes on nearby structures in the vicinity of the proposed structure.

1.6 1.6.1

RAILROAD OVERPASSES Clearances

Structures designed to overpass a railroad shall be in accordance with standards established and used by the affected railroad in its normal practice. These overpass structures shall comply with applicable Federal. State, and local laws. Regulations, codes, and standards should, as a minimum, meet the specifications and design standards of the American Railway Engineering Association, the Association of American Railroads. and AASHTO. 1.6.2

Blast Protection

On bridges over railroads with steam locomotives, metal likely to be damaged by locomotive gases, and all concrete surfaces less than 20 feet above the tracks. shall be protected by blast plates. The plates shall be placed to

DIVISION I—DESIGN

1.6.2

take account of the direction of blast when the locomotive is on level or superelevated tracks by centering them on a line normal to the plane of the two rails at the centerline of the tracks. The plates shall be not less than 4 feet wide and shall be cast-iron, a corrosion and blast-resisting alloy, or asbestos-board shields, so supported that they may be readily replaced. The thickness of plates and other parts in direct contact with locomotive blast shall be not less than 3/4 inch for cast iron, 3/~ inch for alloy 1’ inch for plain asbestos-board, and 7/,~ inch for corrugated asbestos-board. Bolts shall be not less than 5/~ inch in diameter. Pockets which may hold locomotive gases shall be avoided as far as practical. All fastenings shall be galvanized or made of corrosion-resistant material. 1.7

SUPERELEVATION

The superelevation of the Iloor surface of a bridge on a horizontal curve shall be provided in accordance with

5

the standard practice of the commission for the highway construction, except that the superelevation shall not exceed 0.10 foot per foot width of roadway.

1.8

FLOOR SURFACES

All bridge floors shall have skid-resistant characteristics.

1.9

UTILITIES

Where required. provisions shall be made for trolley

wire supports and poles, lighting pillars. electric conduits, telephone conduits, water pipes, gas pipes, sanitary sewers, and other utility appurtenances.

Section 2 GENERAL FEATURES OF DESIGN 2.1

GENERAL

2.1.1 =

b C

=

D

=

d

=

Fa

=

Fb F,

=

F

5

=

=

= =

h

=

L

=

P

=

=

=

w

=

2.2

Notations 2.2.1 area of flanges (Article 2.7.4.3) flange width (Article 2.7.4.3) modification factorfor concentrated load, P, used in the design of rail members (Article 2.7.1.3.1) clear unsupported distance between flange components (Article 2.7.4.3) depth of W or I section (Article 2.7.4.3) allowable axial stress (Article 2.7.4.3) allowable bending stress (Article 2.7.4.2) allowable shear stress (Article 2.7.4.2)

Navigational

Permits for the construction of crossings over navigable streams must be obtained from the U.S. Coast Guard and other appropriate agencies. Requests for such permits from the U.S. Coast Guard should be addressed to the appropriate District Commander. Permit exemptions are allowed on nontidal waterways which are not used as a means to transport interstate or foreign commerce, and are not susceptible to such use in their natural condition or by reasonable improvement.

minimum yield stress (Article 2.7.4.2) axial compression stress (Article 2.7.4.3) height of top rail above reference surface (Figure 2.7.4B) post spacing (Figure 2.7.4B) railing design loading = 10 kips (Article 2.7.1.3 and Figure 2.7.4B) railing design loading equal to R P/2 or P/3 (Article 2.7.1.3.5) flange or web thickness (Article 2.7.4.3) pedestrian or bicycle loading (Articles 2.7.2.2 and

2.2.2

Roadway Width

For recommendations on roadway widths for various volumes of traffic, see AASHTO A Policy on Geometric Design of Highways and Streets, or A Policy on Design Standards—Interstate System. 2.2.3

Vertical Clearance

Vertical clearance on State trunk highways and interstate systems in rural areas shall be at least 16 feet over the entire roadway width with an allowance for resurfacing. On State trunk highways and interstate routes through urban areas, a 16-foot clearance shall be provided except in highly developed areas. A 16-foot clearance should be provided in both rural and urban areas where such clearance is not unreasonably costly and where needed for defense requirements. Vertical clearance on all other highways shall be at least 14 feet over the entire roadway width with an allowance for resurfacing.

2.7.3.2)

2.1.2

STANDARD HIGHWAY CLEARANCES— GENERAL

Width of Roadway and Sidewalk

The width of roadway shall be the clear width measured at right angles to the longitudinal center line of the bridge between the bottoms of curbs. If brush curbs or curbs are not used, the clear width shall be the minimum width measured between the nearest faces of the bridge railing. The width of the sidewalk shall be the clear width, measured at right angles to the longitudinal center line of the bridge, from the extreme inside portion of the handrail to the bottom of the curb orguardtimber. Ifthere is a truss, girder, or parapet wall adjacent to the roadway curb, the width shall be measured to the extreme walk side of these members.

2.2.4

Other

The channel openings and clearances shall be acceptable to agencies having jurisdiction over such matters. Channel openings and clearances shall conform in width, height, and location to all Federal, State, and local requirements. 7

8

2.2.5

HIGHWAY BRIDGES

2.2.5

Curbs and Sidewalks

HORIZONTAL CLEARANCE

The face of the curb is defined as the vertical or s1oping surface on the roadway side of the curb. Horizontal measurements of roadway curbs are from the bottom of the face, or, in the case of stepped back curbs, from the bottom of the lower face. Maximum width of brush curbs,

w 0

maintained across the bridge structure. A parapet or other railing installed at or near the curb line shall have its ends properly flared, sloped, or shielded.

HIGHWAY CLEARANCES FOR BRIDGES

2.3

2.3.1

Width

‘~

2.3.2

Vertical Clearance

The provisions of Arttcle 2 2 3 shall be used. 2.4

I- 0 C,) 4 -J -J .4:

w

OR SIDEWALK IF WARRANTED.

0

I-

I-

F

I-

a: w

z ROADWAY WIDTH

0

a: C.)

FIGURE 2.3.1

Clearance Diagram for Bridges

limits of structure costs, type of structure, volume and design speed of through traffic, span arrangement, skew, and terrain make the 30-foot offset impractical, the pier or wall may be placed closer than 30 feet and protected by the use of guardrail or other barrier devices. The guardrail or other device shall be independently supported with the roadway face at least 2 feet 0 inches from the face of pier or abutment. The face of the guardrail or other device shall be at least 2 feet 0 inches outside the normal shoulder line.

2.4.2

The horizontal clearance shall be the clear width and the vertical clearance the clear height for the passage of vehicular traffic as shown in Fioure 3 I The roadway width shall generally equal the width of the approach roadway section including shoulders. Where curbed roadway sections approach a structure, the same section shall be carried across the structure.

LL 4

(OPTIONAL) 9” (MAX.) BRUSH CURB

if used, shall be 9 inches.

Where curb and gutter sections are used on the roadway approach, at either or both ends of the bridge, the curb height on the bridge may equal or exceed the curb height on the roadway approach. Where no curbs are used on the roadway approaches, the height of the bridge curb above the roadway shall be not less than 8 inches, and preferably not more than 10 inches. Where sidewalks are used for pedestrian traffic on urban expressways, they shall be separated from the bridge roadway by the use of a combination railing as shown in Figure 2.7.4B. In those cases where a New Jersey type parapet or a curb is constructed on a bridge, particularly in urban areas that have curbs and gutters leading to a bridge, the same widths between curbs on the approach roadways will be

z a: w -J

~FACE OF CURB OR BARRIER.

Vertical Clearance

A vertical clearance of not less than 14 feet shall be provided between curbs, or if curbs are not used, over the

entire width that is available for traffic. 2.4.3

Curbs

Curbs, if used, shall match those of the approach roadway section. HIGHWAY CLEARANCES FOR TUNNELS See Figure 2.5.

2.5

HIGHWAY CLEARANCES

FOR UNDERPASSES See Figure 2.4A. 2.4.1

Width

The pier columns or walls for grade separation structures shall generally be located a minimum of 30 feet from the edges of the through-traffic lanes. Where the practical

2.5.1

Roadway Width

The horizontal clearance shall be the clear width and the vertical clearance the clear height for the passage of vehicular traffic as shown in Figure 2.5. Unless otherwise provided, the several parts of the structures shall be constructed to secure the following limiting dimensions or clearances for traffic.

)

DIVISION I—DESIGN

2.5.1

9

AT LEAST 60-OGREATER THAN APPROACH PAVEMENT

~.-FACE OF WALL OR PIER

FACE OF WALL—.. OR PIER

C.)

z Lu I-. Cl,

-J I

C.) C. ILu

L

30-0 MIN.

{

PAVEMENT

z 0

300

MIN.

r

C.)

GENERAL CONDITION

,.-FACE OF WALL OR PIER

K

FACE OF WALL—.

OR PIER

FACE OF BARRIER

FACE OF GUARD RAIL MIN

C.)

z

C.) *

I2-0

Lu

Lu •4<

I- C.)

2-0’ MIN

50 inches

(3-30) (3 - 3 1)

R0 and M0 = shear and moment capacities, respectively, as given in the following table:

DIVISION I—DESIGN

3.25.1.4

3.25.3 Moment Capacity

RD

MD

CR

CM

Required

in-lb. 850 1,340 1,960 2,720 3,630 4,680

2 I/in. 36.9 22.3 14.8 10.5 7.75 5.94

I/in.3

in.

81.5 41.7 24.1 15.2 10.2 7.15

8.50

.875 1.0 1.125 1.25

lb. 600 800 1,020 1,260 1,520 1,790 2,100

10.00 11.50 13.00 14.50 15.50

1.375

2,420

5,950 7,360

4.69 3.78

5.22 3.92

17.00 18.00

1.5

2,770

8,990

3.11

3.02

19.50

Diameter of Dowel in. 0.5 .625 .75

Steel Stress Coefficients

Total Dowel Length

Shear Capacity

3.25.1.5 In addition, the dowels shall be checked to ensure that the allowable stress of the steel is not exceeded using the following equation:

39

Longitudinal Glued Laminated Timber Decks

3.25.3.1

Bending Moment

In calculating bending moments in glued laminated timber longitudinal decks, no longitudinal distribution of wheel loads shall be assumed. The lateral distribution shall be determined as follows. The live load bending moment for each panel shall be determined by applying to the panel the fraction of a wheel load determined frotn the following equations:

TWO

OR MORE TRAFFIC LANES

Load Fraction 1

= — (CR R~ + CM

n

=

_______

M~)

W~ or W~ whichever L 5.00 3.75 ,

1~

(3-32)

is

28

greater. where, (1’

=

mtnttnum yield point of steel pins in pounds per square inch (see Table

ONE TRAFFIC LANE

10.32. IA); n,R 5, M~ = C5, C51 =

3.25.2

as previously delined; steel stress coefficients as given in preceding table.

Plank and Nail Laminated Longitudinal Flooring

3.25.2.1 In the direction of the span, the wheel load shall be considered a point loading. 3.25.2.2 Normal to the direction of the span the wheel load shall be distributed as follows: Plank floor: width of plank; Non-interconnected nail laminated floor: width of tire plus thicktiess of floor, but not to exceed panel width. Continuous nail laminated floor and interconnected nail laminated floor, with adequate shear transfer between panels*, not less than 6 inches thick: width of tire plus twice thickness of floor. 3.25.2.3 For longitudinal flooring the span shall be taken as the clear distance between floor beams plus onehalf the width of one beam but shall not exceed the clear span plus the floor thickness. ~Tltis shear transfer may be accomplished usiitg mechanical fasteners.

splines. or dowels along the panel joint or spreader beams located at intervals along the panels or other suitable means.

Load Fraction =

W~ L 4.25 + 28

W~ s~o

whichever is

iYreater

where, W~ = Width of Panel; in feet (3 5 ~ W~, L

=

=

4.5)

Length of span for simple span bridges and the length of the shortest span for continuous bridges in feet.

3.25.3.2 Shear When calculating the end shears and end reactions for each panel, no longitudinal distribution of the wheel loads shall be assumed. The lateral distribution of the wheel load at the supports shall be that determined by the equation: Wheel Load Fraction per Panel —

but not less than I.

For wheel loads in other positions on the span, the lateral distribution for shear shall be determined by the method prescribed for moment.

40

3.25.3.3

HIGHWAY BRIDGES

3.25.3.3 Deflections

Maximum Bending Moments—Percent of Simple Span Moment Maximum Uniform Dead Load Moments

The maximum deflection may be calculated by applying to the panel the wheel load fraction determined by the method prescribed for moment.

3.25.3.4

Stiffener Arrangement

The transverse stiffeners shall be adequately attached to each panel, at points near the panel edges, with either steel plates, thru-bolts, C-clips or aluminum brackets. The stiffener spacing required will depend upon the spacing needed in order to prevent differential panel movement; however, a stiffener shall be placed at mid-span with additional stiffeners placed at intervals not to exceed 10 feet. The stiffness factor El of the stiffener shall not be less than 80,000 kip-in2. 3.25.4

Continuous Flooring

If the flooring is continuous over more than two spans, the maximum bending moment shall be assumed as being 80 percent of that obtained for a simple span.

3.26

DISTRIBUTION OF WHEEL LOADS AND

DESIGN OF COMPOSITE WOODCONCRETE MEMBERS

Wood Subdeek

Composire Slab

Maximum Live Load Moments Concentrated Load

Uniform Load

Span

Pos.

Neg.

Pos.

Neg.

Pos.

Neg.

Pos.

Neg.

Interior End 2-Span

50

50 60 70

55

45

25 30 30

55

60 75

75 85 85

75

70 60

85

65

80

75

70 65

~Continuousbeam of2 equal spans.

3.26.2.2 Impact should be considered in computing stresses for concrete and steel, but neglected for wood.

3.26.3

Design

The analysis and design of composite wood-concrete members shall be based on assumptions that account for the different mechanical properties of the components. A suitable procedure may be based on the elastic properties of the materials as follows: = I for slab in which the net concrete thickness is less than half the overall depth of the composite section Ec = 2 for slab in which the net concrete thickness ts

at least half the overall depth of the composite section (for Douglas fir and Southern pine)

= 18.75

3.26.1

Distribution of Concentrated Loads for Bending Moment and Shear

in which,

3.26.1.1 For freely supported or continuous slab spans of composite wood-concrete construction, as described in Article 20.19.1 Division II, the wheel loads shall be distributed over a transverse width of 5 feet for bending moment and a width of 4 feet for shear.

= = =

3.27 3.26.1.2 For composite T-beams of wood and concrete, as described in Article 20.19.2—Division II, the effective flange width shall not exceed that given in Article 10.38.3. Shear connectors shall be capable of resisting both vertical and horizontal movement. 3.26.2

Distribution of Bending Moments in Continuous Spans

3.26.2.1 Both positive and negative moments shall be distributed in accordance with the following table:

3.27.1

modulus of elasticity of concrete; modulus of elasticity of wood; modulus of elasticity of steel.

DISTRIBUTION OF WHEEL LOADS ON STEEL GRID FLOORS* General

3.27.1.1 The grid floor shall be designed as continuous, but simple span moments may be used and reduced as provided in Article 3.24.

*ProvisiOns in this article shall not apply to orthotropic bridge superstructures.

3.27.1.2

DIVISION I—DESIGN

3.27.1.2 The following rules for distribution of loads assume that the grid floor is composed of main elements that span between girders, stringers, or cross beams, and secondary elements that are capable of transferring load between the main elements. Reinforcement for secondary elements shall consist of bars or shapes welded to the main steel. 3.27.1.3

3.27.2

Floors Filled with Concrete

3.27.2.1 The distribution and bending moment shall be as specified for concrete slabs, Article 3.24. The following items specified in that article shall also apply to concrete filled steel grid floors: Longitudinal edge beams Unsupported transverse edges Span lengths

41

3.28 DISTRIBUTION OF LOADS FOR BENDING MOMENT IN SPREAD BOX GIRDERS* 3.28.1

Interior Beams

The live load bending moment for each interior beam in a spread box beam superstructure shall be determined by applying to the beam the fraction (D.F.) of the wheel load (both front and rear) determined by the following equation: 2NL S D.F.= +k— (3-33) N~ L where, N 1

k

= number of design tral’fic lanes (Article 3.6); = number of beams (4=N5 = 10); = beam spacing in feet (6.57 = S = 11.00); = span length in feet; = 0.07W N~ (0.10N1 — 0.26) — 0.20N5 — 0.12;

W

=

S L

(3-34)

3.27.2.2 The strength of the composite steel and concrete slab shall be determined by means of the ~‘transformed area” method. The allowable stresses shall be as set forth in Articles 8.15.2, 8.16.1, and 10.32. 3.27.3

Open Floors

3.27.3.1 A wheel load shall be distributed, normal to the main elements, over a width equal to lX~ inches per ton of axle load plus twice the distance center to center of main elements. The portion of the load assigned to each main element shall be applied uniformly over a length equal to the rear tire width (20 inches for H 20, 15 inches forH 15). 3.27.3.2 The strength of the section shall be determined by the moment of inertia method. The allowable stresses shall be as set forth in Article 10.32.

3.28.2

numeric value of the roadway width between curbs expressed in feet (32 = W = 66). Exterior Beams

The live load bending moment in the exterior beams shall be determined by applying to the beams the reaction of the wheel loads obtained by assuming the flooring to act as a stmple span (of length 5) between beatns, but shall not be less than 2N1 IN5. 3.29

MOMENTS, SHEARS, AND REACTIONS

Maximum moments, shears, and reactions are given in tables, Appendix A, for [I 15, H 20, HS 15. and [IS 20 loadings. They are calculated for the standard truck or the lane loading applied to a single lane on freely supported spans. It is indicated in the table whether the standard truck or the lane loadings produces the maximum stress. 3.30 TIRE CONTACT AREA

3.27.3.3 Edges of open grid steel floors shall be supported by suitable means as required. These supports may be longitudinal or transverse, or both, as may be required to support all edges properly. 3.27.3.4 When investigating for fatigue, the mtntmum cycles of maximum stress shall be used.

The tire contact area shall be assumed as a rectangle with an area in square inches of 0.0 IP, and a Length in Direction of Traffic/Width of Tire ratio of 1/2.5, in which P = wheel load in pounds. 5The provisions ofArticle 3.12. Reduction in Load Intensity, were not applied in the development of the provisions presented in 3.28.1 and 3.28.2.

Section 4 FOUNDATIONS Part A GENERAL REQUIREMENTS AND MATERIALS 4.1

GENERAL

4.2.2.2

Foundations shall be designed to support all live and dead loads, and earth and water pressure loadings in accordance with the general principles specified in this section. The design shall be made either with reference to service loads and allowable stresses as provided in SERVICE LOAD DESIGN or, alternatively, with reference to load factors, and factored strength as provided in STRENGTH

Settlement

The settlement of foundations may be determined using procedures described in Articles 4.4, 4.5, or 4.6 for service load design and Articles 4.11, 4.12, or 4.13 for strength design, or other generally accepted methodologies. Such methods are based on soil and rock parameters measured directly or inferred from the results of in situ and/or laboratory tests.

DESIGN.

4.2.2.3 4.2 FOUNDATION TYPE AND CAPACITY 4.2.1

The overall stability of slopes in the vicinity of foundations shall be considered as part of the design of foundations.

Selection of Foundation Type

Selection of foundation type shall be based on an assessment of the magnitude and direction of loading, depth to suitable bearing materials, evidence of previous flooding, potential for liquefaction, undermining or scour, swelling potential, frost depth and ease and cost of construction. 4.2.2

4.2.3

Soil, Rock, and Other Problem Conditions

Geologic and environmental conditions can influence the performance of foundations and may require special consideration during design. To the extent possible, the presence and influence of such conditions shall be evaluated as part of the subsurface exploration program. A representative, but not exclusive, listing of problem conditions requiring special consideration is presented in Table 4.2.3A for general guidance.

Foundation Capacity

Foundations shall be designed to provide adequate structural capacity, adequate foundation bearing capacity with acceptable settlements, and acceptable overall stability of slopes adjacent to the foundations. The tolerable level of structural deformation is controlled by the type and span of the superstructure. 4.2.2.1

Overall Stability

4.3

SUBSURFACE EXPLORATION AND TESTING PROGRAMS

The elements of the subsurface exploration and testing programs shall be the responsibility of the designer based on the specific requirements of the project and his or her experience with local geologic conditions.

Bearing Capacity

The bearing capacity of foundations may be estimated using procedures described in Articles 4.4, 4.5, or 4.6 for service load design and Articles 4.11, 4.12, or 4.13 for strength design, or other generally accepted theories. Such theories are based on soil and rock parameters measured by in situ and/or laboratory tests. The bearing capacity may also be determined using load tests.

4.3.1

General Requirements

As a minimum, the subsurface exploration and testing programs shall define the following, where applicable: • Soil strata —Depth, thickness, and variability 43

HIGHWAY BRIDGES

44 TABLE 4.2.3A

4.3.1

Problem Conditions Requiring Special Consideration

Problem Type

Soil

Description

Comments

Organic soil; highly plastic clay Sensitive clay Micaceous soil

Low strength and high compressibility Potentially large strength loss upon large straining Potentially high compressibility (often saprolitic)

Expansive clay/silt; expansive slag Liquefiable soil

Potentially large expansion upon wetting Complete strength loss and high deformations due to earthquake loading Potentially large deformations upon wetting (Caliche; Loess) Potentially large expansion upon oxidation Low strength when loaded parallel to bedding Potentially large expansion upon wetting; degrades readily upon exposure to air/water Expands upon exposure to air/water

Collapsible soil Pyritic soil Laminated rock Expansive shale Pyritic shale

Rock

Soluble rock Cretaceous shale Weak claystone (Red Beds) Gneissic and Schistose Rock Subsidence Sinkholes/solutioning

Condition

•

• • •

Negative skin friction! expansion loading Corrosive environments Permafrostlfrost Capillary water

Soluble in flowing and standing water (Limestone, Limerock, Gypsum) Indicator of potentially corrosive ground water Low strength and readily degradable upon exposure to air/water Highly distorted with irregular weathering profiles and steep discontinuities Typical in areas of underground mining or high ground water extraction Karst topography; typical of areas underlain by carbonate rock strata Additional compressive/uplift load on deep foundations due to settlementluplift of soil Acid mine drainage; degradation of certain soil/rock types Typical in northern climates Rise of water level in silts and fine sands leading to strength loss

—Identification and classification —Relevant engineering properties (i.e., shear strength, compressibility, stiffness, permeability, expansion or collapse potential, and frost susceptibility) Rock strata —Depth to rock —Identification and classification —Quality (i.e., soundness, hardness, jointing and presence ofjoint filling, resistance to weathering, ifexposed, and solutioning) —Compressive strength (e.g., uniaxial compression, point load index) —Expansion potential Ground water elevation Ground surface elevation Local conditions requiring special consideration

Exploration logs shall include soil and rock strata descriptions, penetration resistance for soils (e.g., SPT or

q~), and sample recovery and RQD for rock strata. The drilling equipment and method, use of drilling mud, type of SPT hammer (i.e. safety, donut, hydraulic) or cone penetrometer (i.e., mechanical or electrical), and any unusual subsurface conditions such as artesian pressures, boulders or other obstructions, or voids shall also be noted on the exploration logs. 4.3.2

Minimum Depth

Where substructure units will be supported on spread footings, the minimum depth of the subsurface exploration shall extend below the anticipated bearing level a minimum of two footing widths for isolated, individual footings where L = 2B, and four footing widths for footings where L> SB. For intermediate footing lengths, the minimum depth of exploration may be estimated by linear interpolation as a function of L between depths of 2B and SB below the bearing level. Greater depths may be required where warranted by local conditions.

4.3.2

Where substructure units will be supported on deep foundations, the depth of the subsurface exploration shall extend a minimum of 20 feet below the anticipated pile or shaft tip elevation. Where pile or shaft groups will be used, the subsurface exploration shall extend at least two times the maximum pile group dimension below the anticipated tip elevation, unless the foundations will be end bearing on or in rock. For piles bearing on rock, a mintmum of 10 feet of rock core shall be obtained at each exploration location to insure the exploration has not been terminated on a boulder. For shafts supported on or extending into rock, a minimum of 10 feet of rock core, or a length of rock core equal to at least three times the shaft diameter for isolated shafts or two times the maximum shaft group dimension for a shaft group, whichever ts greater, shall be obtained to insure the exploration has not terminated in a boulder and to determine the physical characteristics of rock within the zone of foundation influence for design. 4.3.3

Minimum Coverage

A minimum of one soil boring shall be made for each substructure unit. (See Article 7.1.1 for definition of substructure Itnit.) For substructure units over 100 feet in wtdth, a minimum of two borings shall be required. 4.3.4 Laboratory Testing Laboratory testing shall be performed as necessary to determine engineering properties including unit weight, shear strength, compressive strength and compressibility. In the absence of laboratory testing, engineering properties may be estimated based on published test results or local experience. 4.3.5

Scour

The probable depth of scour shall be determined by subsurface exploration and hydraulic studies. Refer to Article 1.3.2 and FHWA (1988) for general guidance regarding hydraulic studies and design. Part B SERVICE LOAD DESIGN METHOD ALLOWABLE STRESS DESIGN 4.4 4.4.1

45

DIVISION I—DESIGN

SPREAD FOOTINGS General

4.4.1.1

4.4.1.2

Footings Supporting Non-Rectangular Columns or Piers

Footings supporting circular or regular polygonshaped concrete columns or piers may be designed assuming that the columns or piers act as square members with the same area for location of critical sections for moment, shear, and development of reinforcement. 4.4.1.3

Footings in Fill

Footings located in fill are subject to the same bearing capacity, settlement, and dynamic ground stability considerations as footings in natural soil in accordance with Articles 4.4.7.1 through 4.4.7.3. The behaviorof both the fill and underlying natural soil shall be considered. 4.4.1.4

Footings in Sloped Portions of Embankments

The earth pressure against the back of footings and columns within the sloped portion of an embankment shall be equal to the at-rest earth pressure in accordance with Article 5.5.2. The resistance due to the passive earth pressure of the embankment in front of the footing shall be neglected to a depth equal to a minimum depth of 3 feet, the depth of anticipated scour, freeze thaw action. and!or trench excavation in front of the footing. whichever is greater. 4.4.1.5

Distribution of Bearing Pressure

Footings shall be designed to keep the maximum soil and rock pressures within safe bearing values. To prevent unequal settlement, footings shall be designed to keep the bearing pressure as nearly uniform as practical. For footings supported on piles or drilled shafts, the spacitig between piles and drilled shafts shall be designed to ensure nearly equal loads on deep foundation elements as may be practical. When footings support more than one column, pier, or wall, distribution of soil pressure shall be consistent with properties of the foundation materials and the structure, and with the principles of geotechnical engineering. 4.4.2 Notations The following notations shall apply for the design of spread footings on soil and rock:

Applicability

Provisions of this Article shall apply for design of isolated footings, and to combined footings and mats (footings supporting more than one column, pier, or wall).

A A’

= =

Contact area of footing (ft2) Effective footing area for computation of bearing capacity of a footing subjected to eccentric load (ft2); (See Article 4.4.7.1. 1.1)

b~, b~, b5 B B’ c

C.

Base inclination factors (dim); (See Article 4.4.7.1.1.8) = Width of footing (ft); (Minimum plan dimension of footing unless otherwise noted) = Effective width for load eccentric in direction of short side, L unchanged (ft) = Soil cohesion (ksf) = Effective stress soil cohesion (ksf) = Reduced effective stress soil cohesion for punching shear (ksf); (See Article 4.4.7.1) = Adhesion between footing and foundation soil or rock (ksf); (See Article 4.4.7.1.1.3) 2/yr); (See = Coefficient of consolidation (ft Article 4.4.7.2.3) = Shear strength of upper cohesive soil layer below footing (ksf); (See Article 4.4.7.1.1.7) = Shear strength of lower cohesive soil layer below footing (ksf); (See Article 4.4.7.1.1.7) = Compression index (dim); (See Article =

F, F

=

f

=

FS

=

H

=

Hcri1

= =

Hd

=

H,

=

=

=

—

Recompression index (dim); (See Article 4.4.7.2.3)

C~.

=

Compression ratio (dim); (See Article 4.4.7.2.3)

C 0 Cr~

Uniaxial compressive strength of intact rock (ksf) = Recompression ratio (dim); (See Article

C0.

=

=

4.4.7.2.3)

D

e ef

ep

et

F,,,

Coefficient of secondary compression defined as change in height per log cycle of time (dim); (See Article 4.4.7.2.4) = Influence depth for water below footing (ft); (See Article 4.4.7.1.1.6) = Depth to base of footing (ft) = Void ratio (dim); (See Article 4.4.7.2.3) = Void ratio at final vertical effective stress (dim); (See Article 4.4.7.2.3) = Void ratio at initial vertical effective stress (dim); (See Article 4.4.7.2.3) = Void ratio at maximum past vertical effective stress (dim); (See Article 4.4.7.2.3) = Eccentricity of load in the B direction measured from centroid of footing (ft); (See Artide 4.4.7.1.1.1) = Eccentricity of load in the L direction measured from centroid of footing (ft); (See Article 4.4.7.1.1.1) = Modulus of intact rock (ksf) = Rock mass modulus (ksf); (See Article 4.4.8.2.2)

Soil modulus (ksf) Total force on footing subjected to an tndined load (k); (See Article 4.4.7.1.1.1) Unconfined compressive strength of concrete (kst) Factor of safety against bearing capacity, overturning or sliding shear failure (dim) Depth from footing base to top of second cohesive soil layer for two-layer cohesive soil profile below footing (ft); (See Article 4.4.7.1.1.7)

4.4.7.2.3) Ccr

4.4.2

HIGHWAY BRIDGES

46

~,

i~, t5

=

Height of compressible soil layer (ft) Critical thickness of the upper layer of a two-layer system beyond which the underlying layer will have little effect on the bearing capacity of footings bearing in the upper layer (ft); (See Article 4.4.7.1.1.7) Height of longest drainage path in compressible soil layer (ft) Height of slope (ft); (See Article 4.4.7.1. 1.4) Slope angle from horizontal of ground surface below footing (deg) Load inclination factors (dim); (See Article 4.4.7.1. 1.3)

Influence coefficient to account for rigidity and dimensions of footing (dim); (See Article 4.4.8.2.2) f = Center-to-center spacing between adjacent footings (ft) L = Length of footing (ft) = Effective footing length for load eccentric in direction of long side, B unchanged (ft) = Length (or width) of footing having positive contact pressure (compression) for footing loaded eccentrically about one axis (ft) n Exponential factor relating B/L or L/B ratios for inclined loading (dim); (See Article 4.4.7.1.1.3) N = Standard penetration resistance (blows/ft) N1 = Standard penetration resistance corrected for effects of overburden pressure (blows/ ft); (See Article 4.4.7.2.2) N~,N~,N5= Bearing capacity factors based on the value of internal friction of the foundation soil (dim); (See Article 4.4.7.1) = Modified bearing capacity factor to account for layered cohesive soils below footing (dim); (See Article 4.4.7.1.1.7) = Coefficient factor to estimate q0 for rock (dim); (See Article 4.4.8.1.2) N, = Stability number (dim); (See Article 4.4.7.1.1.4) =

—

I,,

4.4.2 N~, N.~

P

q

Q q.

q2

R r RQD

S.

S.

DIVISION I—DESIGN Modified bearing capacity factors for effects of footing on or adjacent sloping ground (dim); (See Article 4.4.7.1.1.4) = Tangential component of force on footing (k) = Maximum resisting force between footing base and foundation soil or rock for sliding failure (k) = Effective overburden pressure at base of footing (ksf) = Normal component of force on footing (k) = Allowable uniform bearing pressure or contact stress (ksf) = Cone penetration resistance (ksf) = Maximum footing contact pressure (ksf) Maximum normal component of load supported by foundation soil or rock at ultimate bearing capacity (k) = Minimum magnitude of footing contact pressure (ksf) = Vertical stress at base of loaded area (ksf); (See Article 4.4.7.2.1) = Ultimate bearing capacity for uniform bearing pressure (ksf) = Ultimate bearing capacity of footing supported in the upper layer of a two-layer system assuming the upper layer is infinitely thick (ksf); (See Article 4.4.7.1.1.7) =

Ultimate bearing capacity of a fictitious footing of the same size and shape as the actual footing, but supported on surface of the second (lower) layer of a two-layer system (ksf); (See Article 4.4.7.1.1.7) = Resultant of pressure on base of footing (k) = Radius of circular footing or B/2 for square footing (ft); (See Article 4.4.8.2.2)

T

= Time factor (dim); (See Article 4.4.7.2.3) = Depth from footing base down to the high-

est anticipated ground water level (ft); (See Article 4.4.7.1.1.6) = Angle of inclination of the footing base from the horizontal (radian) = Reduction factor (dim); (See Article 4.4.8.2.2) = Length to width ratio of footing (dim) = Punching index = BL/[2(B + L)H] (dim); (See Article 4.4.7.1.1.7) = Factor to account for footing shape and rigidity (dim); (See Article 4.4.7.2.2) = Total unit weight of soil or rock (kcf) = Buoyant unit weight of soil or rock (kcf) = Moist unit weight of soil (kcf) = Angle of friction between footing and foundation soil or rock (deg); (See Article 4.4.7.1.1.3) = Differential settlement between adjacent footings (ft); (See Article 4.4.7.2.5) = Vertical strain (dim); (See Article 4.4.7.2.3) = Vertical strain at final vertical effective stress (dim); (See Article 4.4.7.2.3) = Initial vertical strain (dim); (See Article

a

y

4.4.7.2.3)

0 K

Pc

p

Article

4.4.7.1.1.2) Undrained shear strength of soil (ksf) Consolidation settlement (ft); (See Article 4.4.7.2.3) = Elastic or immediate settlement (ft); (See Article 4.4.7.2.2) = Secondary settlement (ft); (See Article = =

4.4.7.2.4)

S

= =

=

Total settlement (ft); (See Article 4.4.7.2) Time to reach specified average degree of consolidation (yr); (See Article 4.4.7.2.3) Arbitrary time intervals for determination of 5, (yr); (See Article 4.4.7.2.4)

Vertical strain at maximum past vertical effective stress (dim); (See Article 4.4.7.2.3) = Angle of load eccentricity (deg) = Shear strength ratio (c2/c1) for two layered cohesive soil system below footing (dim); (See Article 4.4.7.1.1.7) = Reduction factor to account for three-dimensional effects in settlement analysis (dim); (See Article 4.4.7.2.3) = Poisson’s ratio (dim) = Final vertical effective stress in soil at depth interval below footing (ksf); (See Article 4.4.7.2.3) = Initial vertical effective stress in soil at depth interval below footing (ksf); (See Article 4.4.7.2.3) = Maximum past vertical effective stress in soil at depth interval below footing (ksf); (See Article 4.4.7.2.3) = Angle of internal friction (deg) = Effective stress angle of internal friction (deg) = Reduced effective stress soil friction angle for punching shear (ksf); (See Article =

=

= Rock Quality Designation (dim) = Footing shape factors (dim); (See

47

*

4.4.7.1)

The notations for dimension units include the following: dim = Dimensionless; deg = degree; ft = foot; k = kip; k/ft = kip/ft; ksf = kip/ft2; kef = kip/ft3; lb = pound; in. = inch; and psi = pound per square inch. The dimensional units provided with each notation are presented for illustration only to demonstrate a dimensionally correct combination of units for the footing capacity procedures presented herein. If other units are used, the dimensional correctness of the equations shall be confirmed.

4.4.4

Soil and Rock Property Selection

Soil and rock properties defining the strength and compressibility characteristics of the foundation materials are required for footing design. Foundation stability and settlement analyses for design shall be conducted using soil and rock properties based on the results of field and/or laboratory testing. 4.4.5

4.4.3

4.4.2

HIGHWAY BRIDGES

48

Depth

4.4.5.1

Design Terminology

Refer to Figure 4.4.3A for terminology used in the design of spread footing foundations.

Minimum Embedment and Bench Width

Footings not otherwise founded on sound, non-dcgradeable rock surfaces shall be embedded a sufficient

0 MAX

FIGURE 4.4.3A

Design Terminology for Spread Footing Foundations

4.4.5.1

DIVISION I—DESIGN

depth to provide adequate bearing, scour and frost heave protection, or 2 feet to the bottom of footing, whichever is greatest. For footings constructed on slopes, a minimum horizontal distance of 4 feet, measured at the top of footing, shall be provided between the near face of the footing and the face of the finished slope. 4.4.5.2 Scour Protection Footings supported on soil or degradable rock strata shall be embedded below the maximum computed scour depth or protected with a scour countermeasure. Footings supported on massive, competent rock formations which are highly resistant to scour shall be placed directly on the cleaned rock surface. Where required, additional lateral resistance should be provided by drilling and grouting steel dowels into the rock surface rather than blasting to embed the footing below the rock surface. Footings on piles may be located above the lowest anticipated scour level provided the piles are designed for this condition. Assume that only one-half of the maximum anticipated scour has occurred when designing for earthquake loading. Where footings on piles are subject to damage by boulders or debris during flood scour, adequate protection shall be provided. Footings shall be constructed so as to neither pose an obstacle to water traffic nor be exposed to view during low flow. 4.4.5.3

Footing Excavations

Footing excavations below the ground water table, particularly in granular soils having relatively high permeability, shall be made such that the hydraulic gradient in the excavation bottom is not increased to a magnitude that would cause the foundation soils to loosen or soften due to the upward flow of water. Further, footing excavations shall be made such that hydraulic gradients and material removal do not adversely affect adjacent structures. Seepage forces and gradients may be evaluated by flow net procedures or other appropriate methods. Dewatering or cutoff methods to control seepage shall be used where necessary. Footing excavations in nonresistant, easily weathered moisture sensitive rocks shall be protected from weathering immediately after excavation with a lean mix concrete or other approved materials. 4.4.5.4 Piping Piping failures of fine materials through rip-rap or through drainage backfills behind abutments shall be pre-

49

vented by properly designed, graded soil filters or geotextile drainage systems. 4.4.6 Anchorage Footings founded on inclined, smooth rock surfaces and which are not restrained by an overburden of resistant material shall be effectively anchored by means of rock anchors, rock bolts, dowels, keys, benching or other suitable means. Shallow keying or benching of large footing areas shall be avoided where blasting is required for rock removal. 4.4.7

Geotechnical Design on Soil

Spread footings on soil shall be designed to support the design loads with adequate bearing and structural capacity, and with tolerable settlements in conformance with Articles 4.4.7 and 4.4.11. In addition, the capacity of footings subjected to seismic and dynamic loads, shall be evaluated in conformance with Articles 4.4.7.3 and 4.4.10. The location of the resultant of pressure (R) on the base of the footings shall be maintained within B/6 of the cenIcr of the footing. 4.4.7.1

Bearing Capacity

The ultimate bearing capacity (for general shear failure) may be estimated using the followingrelationship for continuous footings (i.e., L> SB): =

cN~

+

0.5yBN~

+ qNq

(4.4.7.bi)

The allowable bearing capacity shall be determined as: (4.4.7.1-2)

= q~~/FS

Refer to Table 4.4.7. lA for values of N~, N~, and N~ If local or punching shear failure is possible, the value of q,tt may be estimated using reduced shear strength parameters c* and ~* in 4.4.7.1-I as follows: = =

(4.4.7.1-3)

0.67c

tant (O.67tan

(I))

(4.4.7.1-4)

Effective stress methods of analysis and drained shear strength parameters shall be used to determine bearing capacity factors for drained loading conditions in all soils. Additionally, the bearing capacity of cohesive soils shall

4.4.7.1

HIGHWAY BRIDGES

50

TABLE 4.4.7.1A Bearing Capacity Factors Nq N. 1 1.00 26 22.25 0.00 1.09 27 23.94 0.07 1.20 28 25.80 0.15 1.31 29 27.86 0.24 1.43 30 30.14 0.34 1.57 31 32.67 0.45 1.72

•

0

5.14

1

5.38 5.63 5.90

2

3

6.19 6.49 6.81

4 5

6 7 8 9 10 11 12 13

14 15

16 17

7.16 7.53 7.92 8.35 8.80 9.28 9.81

1.88

10.37 10.98 11.63

3.59

19

12.34 13.10 13.93

20

14.83

21

15.82 16.88

18

22 23 24 25

2.06

2.25 2.47 2.71 2.97 3.26 3.94 4.34

4.77 5.26

0.57 0.71 0.86 1.03

1.22 1.44

1.69 1.97 2.29 2.65

3.06 3.53

5.80 6.40

4.07

7.07

5.39

7.82

6.20

18.05

8.66

7.13

19.32

9.60 10.66

8.20 9.44

20.72

4.68

32

35.49

33 34

38.64 42.16

35

46.12

36 37 38 39

50.59

40 41 42

75.31 83.86 93.71

43

105.11

44 45

118.37 133.88

55.63

61.35 67.87

46

152.10

47 48

173.64 199.26

49

229.93

50

266.89

Nq

N.1

11.85

12.54 14.47 16.72 19.34

13.20

14.72

16.44

22.40

18.40 20.63 23.18 26.09

25.99

30.22

35.19 41.06

29.44

33.30

48.03 56.31 66.19

37.75 42.92 48.93

78.03

55.96 64.20

92.25 109.41

130.22

73.90 85.38 99.02 115.31 134.88 158.51

155.55

186.54 224.64 271.76 330.35 403.67 496.01

187.21 222.31

613.16

265.51 319.07

762.89

10.88 be checked for undrained loading conditions using bearing capacity factors based on undrained shear strength parameters. 4.4.7.1.1

Factors Affecting Bearing Capacity

A modified form of the general bearing capacity equation may be used to account for the effects of footing shape, ground surface slope, base inclination, and inclined

loading as follows: quti

=

cN~s~b~i.

+

O.5yBN~s.~b~i~

+ qNqsqbqiq

calculate the ultimate load capacity of the footing. The reduced footing dimensions shall be determined as follows: 2eB

B’ = B

—

L

—

2eL

(4.4.7.1.1.1-2)

The effective footing area shall be determined as follows: A’ =B’L’

(4.4.7.1.1.1-3)

Refer to Figure 4.4.7.1.1.1 A for loading definitions and Reduced footing dimensions shall be used to account for the effects of eccentric loading. 4.4.7.1.1.1

Eccentric Loading

For loads eccentric relative to the centroid of the footing, reduced footing dimensions (B’ and L’) shall be used to determine bearing capacity factors and modifiers (i.e., slope, footing shape, and load inclination factors), and to

footing dimensions. The value of q,~ obtained using the reduced footing di-

mensions represents an equivalent uniform bearing pressure and not the actual contact pressure distribution beneath the footing. This equivalent pressure may be multiplied by the reduced area to determine the ultimate load capacity of the footing from the standpoint of bearing capacity. The actual contact pressure distribution (i.e., trapezoidal for the conventional assumption of a rigid

4.4.7.1. 1.1

DIVISION I—DESIGN

footing and a positive pressure along each footing edge) shall be used for structural design of the footing. The actual distribution of contact pressure for a rigid footing with eccentric loading about one axis is shown in Figure 4.4.7.l.l.lB. For an eccentricity (eL) in the L direction, the actual maximum and minimum contact pressures may be determined as follows:

51

i~, =1— (nPIBLcN~) (for

n

(4.4.7.1.1.3-2)

4) =0)

= [1

—

P/(Q + BLc cot4))P

(4.4.7.1.1.3-3)

= [1

—

P/(Q + BLccot4))]tn+t)

(4.4.7.1.1.3-4)

= [(2 + UB)/(l + UB)]cos26 + [(2 + B/L)I(l + B/L)]sin2O

(4.4.7.1.1.3-5)

for eL < L/6: qmax =

=

for L/6

<

e~

<

Q[l + (6eL/L)]/BL

(4.4.7.1.1.1-4)

Q[l

(4.4.7.1.1.1-5)

—

(6eL/L)]/BL

L/2:

= 2Q/(3B[L/2)

—

eL])

(4.4.7.1.1.1-6)

Refer to Figure 4.4.7.1.1.1A for loading definitions and footing dimensions. For cases in which the loading is eccentric, the terms Land B shall be replaced by L’ and B’, respectively, in the above equations. Failure by sliding shall be considered by comparing the tangential component offorce on the footing (P) to the maximum resisting force (Pmax) by the following: Pmax

=

Qtan~

+ BLCa

(4.4.7.1.1.3-6)

(4.4.7.1.1.1-7) =

—

3[(L/2)

0

FS=P —

eLI

(4.4.7.1.1.1-8)

For an eccentricity (en) in the B direction, the maximum and minimum contact pressures may be determined using Equations 4.4.7.1.1.1-4 through 4.4.7.1.1. 1-8 by replacing terms labeled L by B, and terms labeled B by L. Footings on soil shall be designed so that the eccentricity of loading is less than 1/6 of the footing dimension in any direction. 4.4.7.1.1.2

Footing Shape

For footing shapes other than continuous footings (i.e., L < SB), the following shape factors shall be applied to Equation 4.4.7.1.1-1: Sc =

1 +

(B/L) (Nq/Nc)

Sq =1 + (B/L) tan = 1

—

4)

0.4 (B/L)

(4.4.7.1.1.2~i) (4.4.7.1.1.2-2)

ma,/p:a. —

In determining ~,,,a,, the effect of passive resistance provided by footing embedment shall be ignored, and BL shall represent the actual footing area in compression as shown in Figure 4.4.7.l.l.lB or Figure 4.4.7.l.l.IC. 4.4.7.1.1.4

Ground Surface Slope

For footings located on slopes or within 3B of a slope crest, quL may be determined using the following revised version of Equation 4.4.7.1.1-1: = cN~s,~bt. + 05y’BN. 5qSybyiy

Inclined Loading

For inclined loads, the following inclination factors shall be applied in Equation 4.4.7.1.1-I: —

[(1

—

iq)/Nc tan

4)] (for 4) >

(4.4.7.1.I.41)

Refer to Figure 4.4.7.1.1 .4A for values of N~ and N.~ for footings on slopes and Figures 4.4.7.1.1 .4B for values of N~ and Nyq for footings at the top of slopes. For footings in or above cohesivesoil slopes, the stability number in the figures, N,, is defined as follows: N, = yH,/c

= i~

(4.4.7.1.1.3-7)

(4.4.7.1.1.2-3)

For circular footings, B equals L. For cases in which the loading is eccentric, the terms L and B shall be replaced by L’ and B’, respectively, in the above equations. 4.4.7.1.1.3

1.5

0) (4.4.7.1.1.3-1)

(4.4.7.1.1.4-2)

Overall stability shall be evaluated for footings on or adjacent to sloping ground surfaces as described in Article 4.4.9. 4.4.7.1.1.5 Embedment Depth The shear strength of soil above the base of footings is neglected in determining quti using Equation 4.4.7.1.L~I. If other procedures are used, the effect of embedment shall be consistent with the requirements of the procedure followed.

52

4.4.7.1.1.5

HIGHWAY BRIDGES

Q

FIGURE 4.4.7.l.l.1A Definition Sketch for Loading and Dimensions for Footings Subjected to Eccentric or Inclined Loads

Modified after EPRI (1983)

I

eL

B

q

‘IT

mi max

I7-t CONTACT PRESSURE

(a)

FOR

e

1

FIGURE 4.4.7.1.l.lB

~

LU

CONTACT PRESSURE

6

12

Contact Pressure for Footing Loaded Eccentrically About One Axis

q

max

RESULTANT

DIVISION I—DESIGN

4.4.7.1.1.5

53

02 6)

II C,

z 0 0 C 0

I-

z

LjJ C.., L&4

~‘>

>~‘

~~j;{1.0

C’,

z

0 0

5 LONGITUDINAL ECCENTRICITY / LENGTh OF FOOTING SOLID CURVES GIVE VALUES OF K. MAXIMUM PRESSURE q,~ K x R/BL

eL/L

—

FIGURE 4.4.7.I.I.IC

Contact Pressure for Footing Loaded Eccentrically About Two Axes

Modified after AREA (1980)

54

HIGHWAY BRIDGES

4.4.7.1.1.5

enterpadolion Urn inl.rmedaofe depths I 1 An*l. of internal IEfJecIive friction

•,

I

N1zO (FOR B’cH,) = VHI(FO ~ RB~H,)

Distance of Ioundotion from edge of slope b/B Distance of faundalimi Vram edge of slope WB(lo, N5;O)or b/H (for t4-O1

(a)

GEOMETRY

(b) COHESIVE SOIL

FIGURE 4.4.7.l.l.4A

Cc) COHESIONLESS SOIL

Modified Bearing Capacity Factors for Footing on Sloping Ground Modified after Meyerhof (1957)

N 5zO (FOR OcH,)

Distance of Ioemdafaan from edge of slope b/B (I.., N,~OJor UNties’ %.O)

(a)

GEOMETRY FIGURE 4.4.7.1.I.4B

(b) COHESIVE SOIL

Distance of foundaUoe from edge of slop. b/B

Cc) COHESIONLESS SOIL

Modified Bearing Capacity Factors for Footing Adjacent Sloping Modified after Meyerhof (1957)

Ground

DIVISION I—DESIGN

4.4.7.1.1.6 4.4.7.1.1.6

Ground Water

= (2D

Ultimate bearing capacity shall be determined using the highest anticipated ground water level at the footing location. The effect of ground water level on the ultimate bearing capacity shall be considered by using a weighted average soil unit weight in Equation 4.4.7.1.1-I. If 4) < the following equations may be used to determine the weighted average unit weight: 370

for z~

= B:

use y

= Ym

for z,.

< B:

use y

=

(no effect)

y’ +

55

(zw/B)(~ym

(4.4.7.1.1.6-I) —

y’)

—

zj(z,c’yn,/D2)

+

(-y’/D2)(D

—

(4.4.7.1.1.6-4) D = O.SBtan(450 +

4)/2) (4.4.7.1.1.6-5)

4.4.7.1.1.7

Loyered Soils

Ifthe soil profile is layered, the general bearing capacity equation shall be modified to account for differences in failure modes between the layered case and the homogeneous soil case assumed in Equation 4.4.7.1 .1 I. -

(4.4.7.1.1.6-2) Undrained Loading

forz_ _ ‘~O:useyy’

(4.4.7.1.1.6-3)

Refer to Figure 4.4.7.l.l.6A for definition of terms used in these equations. If 4) = the following equations may be used to determine the weighted average unit weight: 370

For undrained loading of a footing supported on the upper layer of a two-layer cohesive soil system, q, 1, may be determined by the following: =

c1N,,,

+

q

(4.4.7.l.l.7-l)

‘in,

zw W.T.

$ V

FIGURE 4.4.7.l.1.6A Definition Sketch for Influence of Ground

Water Table on Bearing Capacity

4.4.7.1.1.7

HIGHWAY BRIDGES

56

Refer to Figure 4.4.7.1.1 .7A for the definition ofc1. For undrained loading, c1 equals the undrained soil shear strength s,,i, and 4) = 0. If the bearing stratum is a cohesive soil which overlies a stiffer cohesive soil, refer to Figure 4.4.7.1.1 .7B to determine Nut. If the bearing stratum overlies a softer layer, punching shear should be assumed and N,,, may be calculated by the following: Nm = (l/~3,,, + Ks,,N~)

=

s,,N.

(4.4.7.1.1.7-2)

Drained Loading For drained loading of a footing supported on a strong layer overlying a weak layer in a two-layer system, q~ may be determined using the following: tcot4) quit = [q2 t (l/K)c1 1’] exp + {2[l + (B/L)]Ktan4)1’(I-IIB)}

—

(l/K)c1’ cot4)t’ (4.4.7.1.1.7-3)

The subscripts 1 and 2 refer to the upper +andsin24) lower 24)t’)/(l t) layers, respectively. K = (I sin 1 and q 2 equals q,~1, of a fictitious footing of the same size and shape as the actual footing but supported on the second (or lower) layer. Reduced shear strength values shall be used to detennine q2 in accordance with Article 4.4.7.1. If the upper layer is a cohesionless soil and 4)’ equals 25~ to 50~, Equation 4.4.7.1.1.7-3 reduces to: —

=

q2exp{0.67[l

+ (B/L)]HIB}

(4.4.7.1.1.7-4)

The critical depth of the upper layer beyond which the bearing capacity will generally be unaffected by the presence of the lower layer is given by the following: Hc,,t = l3Bln(q1/q2)]/112(l + Bit)]

(4.4.7.1.1.7-5)

In the equation, q, equals the bearing capacity of the upper layer assuming the upper layer is of infinite extent.

U

z

C U

a Stiff le~w c1, ~

U

a a.

‘a a

C

a U ‘U S

‘U

0

Undrained sirenqth ratiO5 c2/e1 (bI

FIGURE 4.4.7.l.1.7A Typical Two-Layer Soil Profiles

FIGURE 4.4.7.l.1.7B Modified Bearing Capacity Factor for Two-Layer Cohesive Soil with Softer Soil Overlying Stiffer Soil EPRI (1983)

4.4.7.1.1.8

DIVISION I—DESIGN S~

Inclined Base

4.4.7.1.1.8

Footings with inclined bases are generally not recommended. Where footings with inclined bases are necessary, the following factors shall be applied in Equation 4.4.7.1. 1-1:

bq =b~ b~= b~

—

(1

—

= (1

2

—

atan4))

(4.4.7.1.1.8-1)

by)/(N~tan4)) (for 4) > 0) (4.4.7.1.1.8-2)

= I

—

57

[2cy./QTT+ 2)]

(for

4) =

0)

(4.4.7.1.1.8-3)

= Sc + Sc +

5,.

(4.4.7.2-I)

Elastic settlement shall be determined using the unfactored dead load, plus the unfactored component of live and impact loads assumed to extend to the footing level. Consolidation and secondary settlement may be determined using the full unfactored dead load only. Other factors which can affect settlement (e.g., embankment loading, lateral andlor eccentric loading, and for footings on granular soils, vibration loading from dynamic live loads or earthquake loads) should also be considered, where appropriate. Refer to Gifford, et al., (1987) for general guidance regarding static loading conditions and Lam and Martin (1986) for guidance regarding dynamic/seismic loading conditions.

Refer to Figure 4.4.7.1.1 .8A for definition sketch. Where footings must be placed on sloping surfaces, refer to Article 4.4.6 for anchorage requirements. 4.4.7.1.2 Factors of Safety Spread footings on soil shall be designed for Group 1 loadings using a minimum factor of safety (FS) of 3.0 against a bearing capacity failure.

4.4.7.2

Settlement

The total settlement includes elastic, consolidation, and secondary components and may be determined using the following:

4.4.7.2.1

Stress Distribution

Figure 4.4.7.2. lA may be used to estimate the distribution of vertical stress increase below circular (or square) and long rectangular footings (i.e., where L > SB). For other footing geometries, refer to Poulos and Davis (1974). Some methods used for estimating settlement of footings on sand include an integral method to account for the effects of vertical stress increase variations. Refer to Gifford, et al., (1987) for guidance regarding application of these procedures.

GROUND

a

2 FIGURE 4.4.7.l.1.8A Definition Sketch for Footing Base Inclination

4.4.7.2.2

HIGHWAY BRIDGES

58 4.4.7.2.2

Elastic Settlement

The elastic settlement of footings on cohesionless soils and stiff cohesive soils may be estimated using the following: —

(q0(l

—

v2)\/X]/E43,

(4.4.7.2.2-1)

Refer to Table 4.4.7.2.2A for approximate values of E, and v for various soil types, and Table 4.4.7.2.2B for values of ~ for various shapes of flexible and rigid footings. Unless E,. varies significantly with depth, E, should be de-

termined at a depth of about /2 to 2/~ of B below the footing. If the soil modulus varies significantly with depth, a weighted average value of E~ may be used. Refer to Gifford, et al., (1987) for general guidance regarding the estimation of elastic settlement of footings on sand.

4.4.7.2.3

Consolidation Settlement

The consolidation settlement of footings on saturated or nearly saturated cohesive soils may be estimated using

h—S —I

£ £

U

U

InfimIely Lang Faundatsmn (es)

Square FoundatiOn

(IsJ

FIGURE 4.4.7.2.lA Boussinesg Vertical Stress Contours for Continuous and Square Footings Modified after Sowers (1979)

4.4.7.2.3

59

DIVISION I—DESIGN TABLE 4.4.7.2.2A

Elastic Constants of Various Soils

Modified after U.S. Department of the Navy (1982) and Bowles (1982) Estimating E~ From Ntt~

Typical Range of Values Young’s Modulus, E,.

Soil Type

(ksf)

Clay: Soft sensitive Medium stiff to stiff Very stiff

50-300 300-1,000 1,000-2,000

Poisson’s Ratio, v (dim)

0.4-0.5 (undrained)

Soil Type

(ksf)

Silts, sandy silts, slightly cohesive mixtures

8N 1 (2)

Clean fine to medium sands

and slightly silty sands

I 4N1

Coarse sands and sands with

20N~

little gravel Loess Silt

Dense

Sand: Loose Medium dense Dense Gravel: Loose

Medium dense Dense

t3t~

141q.

0.1-0.3 0.3-0.35

40-400

Fine sand: Loose Medium dense

(tiN

300-1,200

160-240 240-400 400-600

0.25

200-600

0.2-0. 35

600-1,000 1,000-1,600

0.3-0.4

600-1,600 1,600-2,000 2,000-4,000

0.2-0.35

Sandy gravel and gravels

24N1

Estimating E~ From ~ Soft sensitive clay 400s~- 1 .OOOs,, Medium stiff to stiff clay

I ,500s,,-2,4.00s~

Very stiff clay

3,000s~-4,000s~

Estimating E, From q~(*) Sandy soils 4q

0.3-0.4

Standard Penetration Test (SPT) resistance. — SPT corrected for depth. Undrained shear strength (ksf). — Cone penetration resistance (ksf).

—

TABLE 4.4.7.2.2B

Elastic Shape and Rigidity

Factors EPRI (1983)

Pu UB

Flexible (average)

Rigid

Circular 1

1.04 1.06

1.13 1.08

2

1.09

1.10

3

1.13

1.15

5

1.22

1.24

10

1.41

1.41

60

4.4.7.2.3

HIGHWAY BRIDGES

the following when laboratory test results are expressed in terms of void ratio (e): e

For initial overconsolidated soils (i.e., Cry,’ > o’o’): U

5,, = [H,,/(l + e,,)][(C,,,, log{o’~’/o’,,’} + C,, log{ur’/u~’})]

0

a

(4.4.7.2.3-I)

0

• For initial normally consolidated soils (i.e., a’,,’): = [H,,/(l

+ e,,)I[C,,log(o’~’/o’~’)]

a’~’

=

(4.4.7.2.3-2)

Vertical effecttve stress, a- (log scale)

laboratory test results are expressed in terms of vertical strain (ej, consolidation settlement may be estimated using the following: If

e

For initial overconsolidated soils (i.e., o’~,’ > 5,, =

FIGURE 4.4.7.2.3A Typical Consolidation Compression Curve for Overconsolidated Soil—

Void Ratio Versus Vertical Effective Stress EPRI (1983)

(J’,,’):

H,,[C,,~log(o’~’/a’,,’) + C,,,, log(o’f’/o’~’)] (4.4.7.2.3-3)

e

For initial normally consolidated soils (i.e., o,~,’ a’,,’):

= ‘U =

0

=

H,,C,,,,log(uf’/o’~’)

(4.4.7.2.3-4)

Refer to Figures 4.4.7.2.3A and 4.4.7.2.3B for the definition of terms used in the equations. To account for the decreasing stress with increased depth below a footing, and variations in soil compressibility with depth, the compressible layer should be divided into vertical increments (i.e., typically 5 to 10 feet for most normal width footings for highway applications), and the consolidation settlement of each increment analyzed separately. The total value of 5,, is the summation of 5,, for each increment. If the footing width is small relative to the thickness of the compressible soil, the effect of three-dimensional (3-D) loading may be considered using the following:

U 0

Vertical effective streSs, a- (log scale)

FIGURE 4.4.7.2.3B Typical Consolidation Compression Curve for Overconsolidated Soil— Void Strain Versus Vertical Effective Stress

Overconsolidation ratio, a-’p /a’o I .0

5

10

15

‘a

5cI3~D)

—

P,SCI I-Dj

(4.4.7.2.3-5)

Refer to Figure 4.4.7.2.3C for values of p< The time (t) to achieve a given percentage of the total estimated l-D consolidation settlement may be estimated using the following:

0 U 0

— 0.5 0 U ~0 S

t =

TH,?/c,

(4.4.7.2.3-6)

Refer to Figure 4.4.7.2.3D for values of T for constant and linearly varying excess pressure distributions. See Winterkorn and Fang (1975) for values of T for other ex-

FIGURE 4.4.7.2.3C

Reduction Factor to Account for

Effects ofThree-Dimensional Consolidation Settlement

EPRI (1983)

4.4.7.2.3

DIVISION I—DESIGN

cess pressure distributions. Values of c,, may be estimated from the results of laboratory consolidation testing of undisturbed soil samples or from in-situ measurements using devices such as a piezoprobe or piezocone. 4.4.7.2.4

Secondary Settlement

Secondary settlement of footings on cohesive soil may be estimated using the following: S.

=

C,,,,H,,log(t4t1)

(4.4.7.2.4-I)

t1 is the time when secondary settlement begins (typically at a time equivalent to 90-percent average degree of consolidation), and t2 is an arbitrary time which could represent the service life of the structure. Values of C,~,, may be estimated from the results of consolidation testing of undisturbed soil samples in the laboratory.

4.4.7.2.5

Tolerable Movement

Tolerable movement criteria (vertical and horizontal) for footings shall be developed consistent with the function and type of structure, anticipated service life, and consequences of unacceptable movements on structure performance. Foundation displacement analyses shall be based on the results of in-situ and/or laboratory testing to characterize the load-deformation behavior of the foundation soils. Displacement analyses should be conducted to determine the relationship between estimated settlement and footing bearing pressure to optimize foottng stzc with respect to supported loads. Tolerable movement criteria for foundation settlement shall be developed considering the angular distortion

(&/f) between adjacent footings. 5/fC shall be limited to 0.005 for simple span bridges and 0.004 for continuous span bridges (Moulton, et al., 1985). These 5/fC limits are not applicable to rigid frame structures. Rigid frames shall be designed for anticipated differential settlements based on the results of special analysis. Tolerable movement criteria for horizontal foundations displacement shall be developed considering the potential effects of combined vertical and horizontal movement. Where combined horizontal and vertical displacements are possible, horizontal movements should be limited to I inch or less. Where vertical displacements are small, horizontal displacements should be limited to I /2 inch or less (Moulton, et al. 1985). If estimated or actual movements exceed these levels, special analysis and/or measitres to limit movements should be considered. 4.4.7.3 Dynamic Ground Stability Refer to Division I-A—Seismic Design and Lam and Martin (1986a; 1986b) for guidance regarding the development of ground and seismic parameters and methods used for evaluation of dynamic ground stability. 4.4.8

Geotechnical Design on Rock

Spread footings supported on rock shall be designed to support the design loads with adequate bearing and stritctural capacity and with tolerable settlements in conformance with Articles 4.4.8 and 4.4.11. In addition, the response of footings subjected to seismic and dynamic loading shall be evaluated in conformance with Article 4.4.10. For footings on rock, the location of the resultant

‘rime factor,

T

C 0 C 0 •5~

C 0 U C 4’ U

FIGURE 4.4.7.2.3D

61

Percentage of Consolidation as a Function of Time Factor, T EPRI (1983)

4.4.8

HIGHWAY BRIDGES

62

of pressure (R) on the base of footings shall be maintained within B/4 of the center of the footing. The bearing capacity and settlement of footings on rock is influenced by the presence, orientation and condition of discontinuities, weathering profiles, and other similar features. The methods used for design of footings on rock should consider these factors as they apply at a particular site, and the degree to which they should be incorporated in the design. For footings on competent rock, reliance on simple and direct analyses based on uniaxial compressive rock strengths and RQD may be applicable. Competent rock is defined as a rock mass with discontinuities that are tight or open not wider than YR inch. For footings on less competent rock, more detailed investigations and analyses should be used to account for the effects of weathering, the presence and condition of discontinuities, and other geologic factors.

Figure 4.4.8.l.lA (Peck, et al. 1974). In no instance shall the maximum allowable contact stress exceed the allowable bearing stress in the concrete. The RQD used in Figure 4.4.8.1.1 A shall be the average RQD for the rock within a depth of B below the base of the footing, where the RQD values are relatively uniform within that interval. If rock within a depth of 0.5B below the base of the footing is of poorer quality, the RQD of the poorer rock shall be used to determine q0 4.4.8.1.2

Footings on Broken or Jointed Rock

The design of footings on broken or jointed rock must account for the condition and spacing of joints and other discontinuities. The ultimate bearing capacity of footings on broken or jointed rock may be estimated using the following relationship: quit=N

4.4.8.1 4.4.8.1.1

Bearing Capacity

The allowable contact stress for footings supported on level surfaces in competent rock may be determined using

I

I

Refer to Table 4.4.8.1 .2A for values of Nm,.. Values of should preferably be determined from the results of laboratory testing of rock cores obtained within 2B of the base of the footing. Where rock strata within this interval are variable in strength, the rock with the lowest capacity C0

Footings on Competent Rock

•

(4.4.8.1.2-1)

C

I

I

5200 •1

0 I-

100-Upper

U

a C

50

6

30-

0 U

limit

curve

If

ROD

is

fairly

uniform,

.0

a 3

0

use

20-

If use

4 It.’

•

0

I

20

I

overage

ROD

within

lower

t~

I

40

ROD

60

d

within

~

5/4

d

is

~

B

lower,

ROD

I

80

100

ROD (%) Note. q~1 shall not exceed the unconfined compressive strength of the rock or 0.595 fc of the concrete. FIGURE 4.4.8.I.lA Allowable Contact Stress for Footings on Rock with Tight Discontinuities Peck, et al. (1974)

4.4.8.1.2

63

DIVISION I—DESIGN

should be used to determine quit’ Alternatively, Table 4.4.8.l.2B may be used as a guide to estimate C0. For

mass characteristics must be made. For rock masses which have time-dependent settlement characteristics, the procedure in Article 4.4.7.2.3 may be followed to determine the time-dependent component of settlement.

rocks defined by very poor quality, the value of q01, should be determined as the value of quit for an equivalent soil mass.

4.4.8.2.2 4.4.8.1.3

Where the criteria for competent rock are not met, the influence of rock type, condition of discontinuities and degree of weathering shall be considered in the settlement analysis. The elastic settlement of footings on broken or jointed rock may be determined using the following:

Factors of Safety

Spread footings on rock shall be designed for Group 1 loadings using a minimum factor of safety (FS) of 3.0 against a bearing capacity failure. 4.4.8.2 4.4.8.2.1

Settlement

e

Footings on Competent Rock

For circular (or square) footings; 2)rIiIEm, with I~ =

For footings on competent rock, elastic settlements will generally be less than Y2 inch when footings are designed in accordance with Article 4.4.8.1.1. When elastic settlements of this magnitude are unacceptable or when the rock is not competent, an analysis of settlement based on rock

TABLE 4.4.8.l.2A

Footings on Broken or Jointed Rock

p e

= q0

(1

—

(V~i~)/I3,

v

(4.4.8.2.2-1)

For rectangular footings;

Values of Coefficient Nm. for Estimation of the Ultimate Bearing Capacity of Footings on

Broken or Jointed Rock (Modified after Hoek, (1983)) Rock Mass Quality

General Description

RMR~’~ Rating

NGIt2~ Rating

RQDt3~ (%)

A

B

Nmst4) C

D

E

Excellent

Intactrockwithjointsspaced > 10 feet apart

100

500

95-100

3.8

4.3

5.0

5.2

6.1

Very good

Tightly interlocking, undisturbed rock with rough unweathered joints spaced 3 to 10 feet apart

85

100

90-95

1.4

1.6

1.9

2.0

2.3

Good

Fresh to slightly weathered rock, slightly disturbed with joints spaced 3 to 10 feet apart

65

10

75-90

0.28

0.32

0.38

0.40 0.46

Rock with several sets of mod-

44

1

50-75

0.049

0.056 0.066

0.069 0.081

23

0.1

25-50

0.015

0.016 0.019

0.020 0.024

3

0.01

R5 —~ A~ r9

I

9

RT = At rt

FIGURE 4.5.4A Design Tenninology for Driven Pile Foundations 4.5.6.2

Factor of Safety Selection

The selection of the factor of safety to be applied to the ultimate axial geotechnical capacity shall consider the reliability of the ultimate soil capacity determination and pile installation control. Recommended values for the factor of safety depending upon the degree of construction control specified on the plans are presented in Table 4.5.6.2A. All factors of safety are based on fulltime observation of pile installation. The design pile capacity shall be specified on the plans so the factor of safety can be adjusted if the specified construction control is altered.

4.5.6.3

Settlement

The settlement of axially loaded piles and pile groups at the allowable loads shall be estimated. Elastic analysis, load transfer andlor finite element techniques (e.g., Vesic, 1977 or Poulos and Davis, 1980) may be used. The settlement of the pile or pile group shall not exceed the tolerable movement limits of the structure. 4.5.6.4

Group Pile Loading

Group pile capacity should be determined as the product of the group efficiency, number of piles in the group,

72

4.5.6.4

HIGHWAY BRIDGES TABLE 4.5.6.2A Recommended Factor of Safety on Ultimate Geotechnical Capacity Based on Specified Construction Control Increasing Construction Control

Subsurfacc exploration

Static calculation Dynamic formula

‘X

X

X

X

X

X X

X

X

X

X

X

X

X

X

Wave equation

Dynamic measurement and analysis Static load tcst Factorof safety

X 3.50

2.75

2.25

X X 22.00

X 1.90

Construction Control Specified on Contract 2~For any combination of construction control that Plans. includes an approved static load test a factor of safety of 2.0 may be used.

and the capacity of a single pile. In general, a group efficiency value of 1.0 should be used except for friction piles in cohesive soils. The efficiency factor for friction piles in cohesive soils with a center-to-center pile spacing less than 3.OB should be 0.7. Center-to-center pile spacings less than 2.5B are not recommended. 4.5.6.5

Lateral Loads on Piles

The design of laterally loaded piles is usually governed by lateral movement criteria. The design of laterally loaded piles shall account for the effects of soil/rockstructure interaction between the pile and ground (e.g., Reese, 1984). Methods of analysis evaluating the ultimate capacity or deflection of laterally loaded piles (e.g., Broms, I 964a and I 964b; Singh, et al., 1971) may be used for preliminary design only as a means to evaluate appropriate pile sections. 4.5.6.6

Uplift Loads on Piles

The uplift design capacity of single piles and pile groups shall be determined in accordance with Articles 4.5.6.6.1 and 4.5.6.6.2, respectively. Proper provision shall be made for anchorage of the pile into the pile cap. 4.5.6.6.1

Single Pile

The uplift design capacity for a single pile shall not exceed one-third of the ultimate frictional capacity determined by a static analysis method. Alternatively, the uplift capacity of a single pile can be determined by uplift load tests in conformance with ASTM D-3689 (ASTM, 1988). If determined by load tests, the allowable uplift design capacity shall not exceed 50 percent of the failure uplift load.

4.5.6.6.2

Pile Group

The uplift design capacity for a pile group shall be the lesser of: (I) The single pile uplift design capacity multiplied by the number of piles in the group, or (2) two-thirds of the effective weight of the pile group and the soils contained within a block defined by the perimeter of the group and the embedded length of the piles, or (3) onehalf the effective weight of the pile group and the soil contained within a block defined by the perimeter of the group and the embedded pile length plus one-halfthe total soil shear on the peripheral surface of the group. 4.5.6.7

Vertical Ground Movement

The potential for external loading on a pile by vertical ground movements shall be considered as part of the design. Vertical ground movements may result in negative skin friction or downdrag loads due to settlement of compressible soils or may result in uplift loads due to heave of expansive soils. For design purposes, the full magnitude of maximum vertical ground movement shall be assumed. 4.5.6.7.1

Negative Skin Friction

The potential for external loading on a pile by negative skin frictionldowndrag due to settlement of compressible soil shall be considered as a part of the design. Evaluation of negative skin friction shall include a load-transfer method of analysis to determine the neutral point (i.e., point of zero relative displacement) and load distribution along shaft (e.g., Fellenius, 1984, Reese and O’Neill, 1988). Due to the possible time dependence associated with vertical ground movement, the analysis shall consider the effect of time on load transfer between the ground and shaft and the analysis shall be performed for the time period relating to the maximum axial load transfer to the pile. If necessary, negative skin friction loads that cause excessive settlement may be reduced by application of bitumen or other viscous coatings to the pile surfaces before installation. 4.5.6.7.2

Expansive Soil

Piles driven in swelling soils may be subjected to uplift forces in the zone of seasonal moisture change. Piles shall extend a sufficient distance into moisture—stable soils to provide adequate resistance to swelling uplift forces. In addition, sufficient clearance shall be provided between the ground surface and the underside of pile caps or grade beams to preclude the application of uplift loads at the pile cap. Uplift loads may be reduced by application of bitumen or other viscous coatings to the pile surface in the swelling zone.

73

DIVISION I—DESIGN

4.5.6.8 4.5.6.8

Dynamic/Seismic Design

TABLE 4.5.7.3A Allowable Working Stress for Round Timber Piles

Refer to Division I-A for guidance regarding the design of driven piles subjected to dynamic and seismic loads. 4.5.7

Allowable Unit Working Stress Compression Parallel to Grain for

Structural Capacity of Pile Section

Nortnal Duration of

4.5.7.1

Load Capacity Requirements

Piles shall be designed as structural members capable of safely supporting all loads imposed on them by the structure or surrounding soil. 4.5.7.2 Piles Extending Above Ground Surface For portions of piles in air or water, or in soil not capable of providing adequate lateral support throughoutthe pile length to prevent buckling, the structural design provisions for compression members of Sections 8,9,10, and 13 shall apply except: timber piles shall be designed in accordance with Article 13.5 using the allowable unit stresses given in Article 13.2 for lumber and in Table 4.5.7.3A. 4.5.7.3

Allowable Stresses in Piles

Species

Loading o, (psi)

Ash, white Beech Birch

1,200 1,300 900

Cypress, Southern

1,200

Cypress. Tidewater red

1,200

Douglas Fir, coast type Douglas Fir, inland Elm, rock

1,200

Elm, soft Gum, black and red

Hemlock, Eastern

is unlikely. Static and/or dynamic load test and evaluation confirming satisfactory results should be performed when using 0.33F~. • For unfilled steel pipe piles, the maximum allowable stress shall not exceed 0.2SF~ over the minimum cross-sectional area of the pile. The maximum allowable stress may be increased to 0.33F) in conditions where pile damage is unlikely. Static and/or dynamic load test and evaluation confirming salisfactory results should be performed when using 0.33F~. • For concrete filled steel pipe piles, the maximum allowable stress shall not exceed 0.2SF~ + 0.40f~.’ applied over the cross-sectional area of the steel pipe and on the cross-sectional area of the concrete, respectively.

1,300

850 850 800

1,000

Hickory Larch Maple, hard Oak, red and white Pecan

1,650

Pine, Norway Pine, Southern Pine, Southern, dense Poplar, yellow Redwood Spruce, Eastern

Tupelo

• For steel H-piles, the maximum allowable stress shall not exceed 0.2SF over the cross—sectional area of the pile, not including the area of any tip reinforcement. The maximum allowable stress may be increased to 0.33F5 in conditions where pile damage

1.100

Hemlock, West Coast

Pine, Lodgepole

The maximum allowable stress on a pile shall not exceed the following limits in severe subsurface conditions. Where pile damage or deterioration is possible, it may be prudent to use a lower stress level than the maximum allowable stress.

1,300

Chestnut

1,200

1,300 1,100 1,650 800

850 l,2t)0

1,400 800

1,100 850 850

• For precast concrete piles, the maximum allowable stress shall not exceed 0.33f~ on the gross cross-sec-

tional area of the concrete. • For prestressed concrete piles fully embedded in soils providing lateral support, the maximum allowable stress shall not exceed 0.33E — 0.27f1,~ on the gross cross-sectional area of the concrete. • For round timber piles, the maximum allowable stress shall not exceed the values in Table 4.S.7.3A for the pile tip area. For sawn timber piles, the values applicable to ~~wetcondition” for allowable compression parallel to grain shall be used in accordance with Article 13.2. 4.5.7.4

Cross-Section Adjustment for Corrosion

For concrete-filled pipe piles where corrosion may be expected, Y inch shall be deducted from the shell thick-

74

HIGHWAY BRIDGES

ness to allow for reduction in section due to corrosion. Area of shell shall be included in determining percentage of reinforcement, p. 4.5.7.5

Scour

The probable depth of scour shall be determined by subsurface exploration and hydraulic studies as described in Article 4.3.5. If heavy scour is expected, consideration shall be given to designing the portion of the pile that would be exposed as a column. In all cases, the pile length shall be determined such that the design structural load may be safely supported entirely below the probable scour depth. The pile shall be of adequate cross-section to withstand the driving necessary to penetrate through the anticipated scour depth to the design embedment. 4.5.8

Protection Against Corrosion and Abrasion

Where conditions of exposure warrant, concrete encasement or other corrosion protection shall be used on steel piles and steel shells. Exposed steel piles or steel shells shall not be used in salt or brackish water, and only with caution in fresh water. Where the piling is exposed to the abrasive action of the bed load of materials, the section shall be increased in thickness or positive protection shall be provided. 4.5.9

Wave Equation Analysis

The constructability of the pile foundation design should be evaluated using a wave equation computer program. The wave equation should be used to confirm that the design pile section can be installed to the desired depth, ultimate capacity, and within the allowable driving stress levels specified in Article 4.5.11 using an appropriately sized driving system. 4.5.10

Steel piles Concrete piles

0.90Ff (Compression) 0.90F~ (Tension) 0.8Sf~ (Compression) 0. 70F

5 of Steel Reinforcement (Tension) Prestressed concrete piles 0.85ff f5. (Compression) Normal environments 3 f~’ + f~ (Tension) (fe’ and f~. must be in psi. The resulting max stress is also in psi.) Severe corrosive environments f~. (Tension) Timber piles 3a’~ (Compression) 30’a (Tension) —

Driving stresses may be estimated by performing wave equation analyses or by dynamic monitoring of force and acceleration at the pile head during pile driving. 4.5.12

Tolerable Movement

Tolerable axial and lateraldisplacement criteria for driven pile foundations shall be developed by the structural engineer consistent with the function and type of structure, fixity of bearings, anticipated service life, and consequences of unacceptable displacements on the structural performance. Driven pile displacement analyses shall be based on the results of in-situ and/or laboratory testing to characterize the load deformation behavior of the foundation materials. Refer to Article 4.4.7.2.S for additional guidance regarding tolerable vertical and horizontal movement criteria. 4.5.13

Buoyancy

The effect of hydrostatic pressure shall be considered in the design as provided in Article 3.19.

Dynamic Monitoring

Dynamic monitoring may be specified for piles installed in difficult subsurface conditions such as soils with obstructions and boulders, or a steeply sloping bedrock surface to evaluate compliance with structural pile capacity. Dynamic monitoring may also be considered for geotechnical capacity verification where the size of the project or other limitations deter static load testing. 4.5.11

4.5.7.4

Maximum Allowable Driving Stresses

Maximum allowable driving stresses in pile material for top driven piles shall not exceed the following limits:

4.5.14

Protection Against Deterioration

4.5.14.1

Steel Piles

A steel pile foundation design shall consider that steel piles may be subject to corrosion, particularly in fill soils,

low ph soils (acidic) and marine environments. A field electric resistivity survey, or resistivity testing and ph testing of soil and ground water samples should be used to evaluate the corrosion potential. Methods of protecting steel piling in corrosive environments include use of protective coatings, cathodic protection, and increased pile steel area.

4.5.14.2 Concrete Piles A concrete pile foundation design shall consider that deterioration of concrete piles can occur due to sulfates in soil, ground water, or sea water; chlorides in soils and chemical wastes; acidic ground water and organic acids. Laboratory testing of soil and ground water samples for sulfates and ph is usually sufficient to assess pile deterioration potential. A full chemical analysis of soil and ground water samples is recommended when chemical wastes are suspected. Methods of protecting concrete piling can include dense impermeable concrete, sulfate reststing portland cement, minimum cover requirements for reinforcing steel, and use of epoxies, resins, or other protective coatings. 4.5.14.3 Timber Piles A timber pile foundation design shall consider that deterioration of timber piles can occur due to decay from wetting and drying cycles or from insects or marine borers. Methods of protecting timber piling include pressure treating with creosote or other wood preservers. 4.5.15

75

DIVISION I—DESIGN

4.5. 14.2

Spacing, Clearances, and Embedment

4.5.15.1 4.5.15.1.1

Pile Footings Pile Spacing

Pile footings shall be proportioned such that the minimum center-to-center pile spacing shall exceed the greater of 2 feet 6 inches or 2.5 pile diameters/widths. The distance from the side of any pile to the nearest edge of the pile footing shall not be less than 9 inches. 4.5.15.1.2

Minimum Projection into Cap

The tops of piles shall project not less than 12 inches into concrete after all damaged pile material has been removed, but in special cases, it may be reduced to 6

4.5.16

Precast Concrete Piles

4.5.16.1

Size and Shape

Precast concrete piles shall be of approved size and shape but may be either of uniform section or tapered. In general, tapered piling shall not be used for trestle construction except for the portion of the pile which lies below the ground line; nor shall tapered piles be used in any location where the piles are to act as columns. 4.5.16.2

Minimum Area

In general, concrete piles shall have a cross-sectional area, measured above the taper, of not less than 98 square inches. In saltwater a minimum cross-sectional area of 140 square inches shall be used. Ifa square section is employed, the corners shall be chamfered at least 1 inch. 4.5.16.3

Minimum Diameter of Tapered Piles

The diameter of tapered piles measured at the point shall be not less than 8 inches. In all cases the diameter shall be considered as the least dimension through the center. 4.5.16.4

Driving Points

Piles preferably shall be cast with a driving point and, for hard driving, preferably shall be shod with a metal shoe of approved pattern. 4.5.16.5

Vertical Reinforcement

Vertical reinforcement shall consist of not less than four bars spaced uniformly around the perimeter of the pile, except that if more than four bars are used, the number may be reduced to four in the bottom 4 feet of the pile. The amount of reinforcement shall be at least I Y~ percent of the total section measured above the taper.

inches.

4.5.16.6 4.5.15.2

Spiral Reinforcement

Bent Caps

Where a reinforced concrete beam is cast-in-place and used as a bent cap supported by piles, the concrete cover at the sides of the piles shall be a minimum of 6 inches. The piles shall project at least 6 inches and preferably 9 inches into the cap, although concrete piles may project a lesser distance into the cap if the projection of the pile reinforcement is sufficient to provide adequate bond.

The full length of vertical steel shall be enclosed with spiral reinforcement or equivalent hoops. The spiral reinforcement at the ends of the pile shall have a pitch of 3 inches and gage of not less than No. 5 (U.S. Steel Wire Gage). In addition, the top 6 inches of the pile shall have five turns of spiral winding at I-inch pitch. For the remainder of the pile, the lateral reinforcement shall be a No. 5 gage spiral with not more than 6-inch pitch, or inch round hoops spaced on not more than 6-inch centers.

4.5.16.7

HIGHWAY BRIDGES

76 4.5.16.7

Reinforcement Cover

The reinforcement shall be placed at a clear distance from the face of the pile of not less than 2 inches and, when piles are used in saltwater or alkali soils, this clear distance shall not be less than 3 inches. 4.5.16.8

Splices

Piles may be spliced provided that the splice develops the full strength of the pile. Splices should be detailed on the contract plans. Any alternative method of splicing that provides equal results may be considered for approval. 4.5.16.9

Handling Stresses

In computing stresses due to handling, the static loads shall be increased by 50 percent as an allowance for impact and shock. 4.5.17

Cast-in-Place Concrete Piles

4.5.17.1

equate lateral restraint. Where the shell is smooth pipe and more than 0.12 inch in thickness, it may be considered as load carrying in the absence of corrosion. Where the shell is corrugated and is at least 0.075 inch in thickness, it may be considered as providing confinement in the absence of corroston. 4.5.17.5

Reinforcement into Superstructure

Sufficient reinforcement shall be provided at the junction of the pile with the superstructure to make a suitable connection. The embedment of the reinforcement into the cap shall be as specified for precast piles. 4.5.17.6 Shell Requirements The shell shall be of sufficient thickness and strength so that it will hold its original form and show no harmful distortion after it and adjacent shells have been driven and the driving core, if any, has been withdrawn. The plans shall stipulate that alternative designs of the shell must be approved by the Engineer before any driving is done.

Materials 4.5.17.7

Cast-in-place concrete piles shall be, in general, cast in metal shells that shall remain permanently in place. However, other types of cast-in-place piles, plain or reinforced, cased or uncased, may be used if the soil conditions permit their use and if their design and method of placing are satisfactory.

Splices

Piles may be spliced provided the splice develops the full strength of the pile. Splices should be detailed on the contract plans. Any alternative method of splicing providing equal results may be considered for approval. 4.5.17.8

Reinforcement Cover

4.5.17.2 Shape Cast-in-place concrete piles may have a uniform crosssection or may be tapered over any portion. 4.5.17.3 Minimum Area The minimum area at the butt of the pile shall be 100 inches and the minimum diameter at the tip of the pile shall be 8 inches. Above the butt or taper, the minimum size shall be as specified for precast piles.

The reinforcement shall be placed a clear distance of not less than 2 inches from the cased or uncased sides. When piles are in corrosive or marine environments, or when concrete is placed by the water or slurry displacement methods, the clear distance shall not be less than 3 inches for uncased piles and piles with shells not sufficiently corrosion reststant. 4.5.18

Steel H-Piles

4.5.18.1

Metal Thickness

4.5.17.4 General Reinforcement Requirements Steel piles shall have a minimum thickness of web of

Cast-in-place piles.,carrying axial loads only where the possibility of lateral forces being applied to the piles is insignificant, need not be reinforced where the soil provides adequate lateral support. Those portions of cast-in-place concrete piles that are not supported laterally shall be designed as reinforced concrete columns in accordance with Articles 8.15.4 and 8.16.4, and the reinforcing steel shall extend 10 feet below the plane where the soil provides ad-

0.400 inch. Splice plates shall not be less than 4.5.18.2

>‘~

in. thick.

Splices

Piles shall be spliced to develop the net section of pile. The flanges and web shall be either spliced by butt welding or with plates that are welded, riveted, or bolted. Splices shall be detailed on the contract plans. Prefabri-

4.5.18.2

DIVISION I—DESIGN

cated splicers may be used if the splice can develop the net section of the pile in compression, tension, shear, and bending. 4.5.18.3

Caps

4.5.18.4

Lugs, Scabs, and Core-Stoppers

These devices may be used to increase the bearing capacity of the pile where necessary. They may consist of structural shapes—welded, riveted, or bolted—of plates welded between the flanges, or of timber or concrete blocks securely fastened. 4.5.18.5

Point Attachments

If pile penetration through cobbles, boulders, debris fill or obstructions is anticipated, pile tips shall be reinforced with structural shapes or with prefabricated cast steel points. Cast steel points shall meet the requirements of ASTM A27. 4.5.19

Unfilled Tubular Steel Piles

4.5.19.1

Metal Thickness

Piles shall have a minimum thickness not less than indicated in the following table: Outside Diameter

Less than 14 inches

14 inches and over

Wall Thickness

0.25 inch

0.375 inch

4.5.19.2

Splices

Piles shall be spliced to develop the full section of the pile. The piles shall be spliced either by butt welding or by the use of welded sleeves. Splices shall be detailed on the contract plans. 4.5.19.3

Driving

Tubular steel piles may be driven either closed or open ended. Closure plates should not extend beyond the perimeter of the pile. 4.5.19.4

a portion of the pile, the pile will be investigated for column action. The provisions of Article 4.5.8 shall apply to unfilled tubular steel piles. 4.5.20

In general, caps are not required for steel piles embedded in concrete.

Column Action

Where the piles are to be used as part of a bent structure or where heavy scour is anticipated that would expose

77

Prestressed Concrete Piles

4.5.20.1

Size and Shape

Prestressed concrete piles that are generally octagonal, square or circular shall be of approved size and shape. Air entrained concrete shall be used in piles that are subject to freezing and thawing or wetting and drying. Concrete in prestressed piles shall have a minimum compressive strength, f, of 5,000 psi at 28 days. Prestressed concrete piles may be solid or hollow. For hollow piles, precautionary measures should be taken to prevent breakage due to internal water pressure during driving, ice pressure tn trestle piles, and gas pressure due to decomposition of material used to form the void. 4.5.20.2

Main Reinforcement

Main reinforcement shall be spaced and stressed so as to provide a compressive stress on the pile after losses f general not less than 700 psi to prevent cracking during handling and installation. Piles shall be designed to resist stresses developed during handling as well as under service load conditions. Bending stresses shall be investigated for all conditions of handling, taking into account the weight of the pile plus 50-percent allowance for impact, with tensile stresses limited to 5 f> 4.5.20.3

Vertical Reinforcement

The full length of vertical reinforcement shall be enclosed within spiral reinforcement. For piles up to 24 inches in diameter, spiral wire shall be No. S (U.S. Steel Wire Gage). Spiral reinforcement at the ends of these piles shall have a pitch of 3 inches for approximately 16 turns. In addition, the top 6 inches of pile shall have five turns of spiral winding at 1-inch pitch. For the remainder of the pile, the vertical steel shall be enclosed with spiral reinforcement with not more than 6-inch pitch. For piles having diameters greater than 24 inches, spiral wire shall be No. 4 (U.S. Steel Wire Gage). Spiral reinforcement at the end of these piles shall have a pitch of 2 inches for approximately 16 turns. In addition, the top 6 inches of pile shall have four turns of spiral winding at I Y2 inches. For the remainder of the pile, the vertical steel shall be enclosed with spiral reinforcement with not more than 4inch pitch. The reinforcement shall be placed at a clear distance from the face of the prestressed pile of not less than 2 inches.

4.5.20.4

HIGHWAY BRIDGES

78 4.5.20.4

Hollow Cylinder Piles

Large diameter hollow cylinder piles shall be of approved size and shape. The wall thickness for cylinder piles shall not be less than 5 inches. The grouting of posttensioning tendons shall be in accordance with Article 4.33.9—Division II. 4.5.20.5

Splices

When prestressed concrete piles are spliced, the splice shall be capable of developing the full section of the pile. Splices shall be detailed on the contract plans. 4.5.21

Timber Piles

4.5.21.1

Materials

Timber piles shall conform to the requirements of the Specifications for Wood Products, AASHTO M 168. Timber piles shall be treated or untreated as indicated on the contract plans. Preservative treatment shall conform to the requirements of Section 16, “Preservative Treatments for Lumber.” 4.5.21.2

Limitations on Untreated Timber Pile Use

Untreated timber piles may be used for temporary construction, revetments, fenders, and similar work, and in permanent construction under the following conditions: • For foundation piling when the cutoff is below permanent ground water level. • For trestle construction when it is economical to do so, although treated piles are preferable. • They shall not be used where they will, or may, be exposed to marine borers. • They shall not be used where seismic design considerations are critical. 4.5.21.3 Limitations on Treated Timber Pile Use Treated timber piles shall not be used where seismic design considerations are critical. 4.6 4.6.1

DRILLED SHAFTS General

The provisions of this article shall apply to the design of axially and laterally loaded drilled shafts in soil or extending through soil to or into rock.

4.6.1.1

Application

Drilled shafts may be considered when spread footings cannot be founded on suitable soil or rock strata within a reasonable depth and when piles are not economically viable due to high loads or obstructions to driving. Drilled shafts may be used in lieu of spread footings as a protection against scour. Drilled shafts may also be considered to resist high lateral or uplift loads when deformation tolerances are small. 4.6.1.2 Materials Shafts shall be cast-in-place concrete and may include deformed bar steel reinforcement, structural steel sections, and/or permanent steel casing as required by design. In every case, materials shall be supplied in accordance with the provisions of this Standard. 4.6.1.3

Construction

Drilled shafts may be constructed using the dry, casing, or wet method of construction, or a combination of methods. In every case, hole excavation, concrete placement, and all other aspects of shaft construction shall be performed in conformance with the provisions of this Standard. 4.6.1.4

Embedment

Shaft embedment shall be determined based on vertical and lateral load capacities of both the shaft and subsurface materials 4.6.1.5

Shaft Diameter

For rock-socketed shafts which require casing through the overburden soils, the socket diameter should be at least 6 inches less than the inside diameter of the casing to facilitate drill tool insertion and removal through the casing. For rock-socketed shafts not requiring casing through the overburden soils, the socket diameter can be equal to the shaft diameterthrough the soil. 4.6.1.6

Batter Shafts

The use of battered shafts to increase the lateral capacity of foundations is not recommended due to their difficulty of construction and high cost. Instead, consideration should first be given to increasing the shaft diameter to obtain the required lateral capacity.

4.6.1.7

DIVISION I—DESIGN

4.6.1.7

Shafts Through Embankment Fill

Shafts extending through embankments shall extend a minimum of 10 feet into original ground unless bedrock or competent bearing strata occurs at a lesser penetration. Fill used for embankment construction shall be random fill material having adequate capacity which shall not obstruct shaft construction to the required depth. Negative skin friction loads due to settlement and consolidation of embankment or underlying soils shall be evaluated for shafts in embankments. (See Article 4.6.5.2.5.)

N

N’

= = =

N,

=

P

= =

Q

Notations

The following notations shall apply for the design of drilled shaft foundations in soil and rock: a

bearing factor to account for large diameter shaft tip (dim); (See Article 4.6.5.1.3) 2) = Area of shaft (ft = Area of shaft tip (ft2) = Tip bearing factor to account for large diameter shaft tip (dim); (See Article 4.6.5.1.3) = Shaft diameter (ft); (See Article 4.6.3) = Diameter of enlarged base (ft); (See Article = Tip

A A, b B Bb

4.6.3)

B 1

= Least width of shaft group

(ft); (See Article

4.6.5.2.4.3)

B, B, Cm

= Diameter of rock socket (ft); (See Article 4.6.3) = Tip diameter (ft); (See Article 4.6.5.1.3) = Uniaxial compressive strength of rock mass

C,,

=

D

Em FS

H

1pu

(ksf); (See Article 4.6.5.3.1) Uniaxial compressive strength of intact rock (ksf) = Shaft length (ft); (See Article 4.6.3) = Length of rock socket (ft); (See Article 4.6.3) = Elastic modulus of concrete shaft or reinforced shaft (ksf) = Elastic modulus of intact rock (ksf) = Elastic modulus of rock mass (ksf) = Factor of safety (dim) = Ultimate load transfer along shaft (ksf); (See Articles 4.6.5.1.1 and 4.6.5.1.2) = Distance from shaft tip to top of weak soil layer (ft); (See Article 4.6.5.2.4.3) = Depth interval (dim); (See Articles 4.6.5.1.1 and 4.6.5.1.2) = Displacement influence factor for rock-socketed shafts loaded in compression (dim); (See Article 4.6.5.5.2) = Displacement influence factor for rock-socketed shafts loaded in uplift (dim); (See Article 4.6.5.5.2)

Standard penetration resistance (blows/ft) Standard penetration test blow count corrected for effects of overburden (blows/ft) Bearing capacity factor (dim); (See Article 4.6.5.1.3) Number of depth intervals into which shaft is divided for determination of side resistance (dim); (See Articles 4.6.5.1.1 and 4.6.5.1.2) Lateral load on shaft (k) Total axial compression load applied to shaft butt (k)

Ultimate unit tip capacity for an equivalent shaft for a group of shafts supported in strong layer overlying weaker layer (ksf); (See Article 4.6.5.2.4.3) = Ultimate unit tip capacity of an equivalent shaft bearing in weaker underlying soil layer (ksf); (See Article 4.6.5.2.4.3) = Total axial uplift load applied to shaft butt (k) qup = Ultimate unit tip capacity of an equivalent shaft bearing in stronger upper soil layer (ksf); (See Article 4.6.5.2.4.3) = Ultimate side resistance in soil (k); (See Articles 4.6.5.1.1 and 4.6.5.1.2) qsR = Ultimate unit shear resistance along shaft!rock interface (psi); (See Article 4.6.5.3.1) QSR = Ultimate side resistance of rock socket (k); (See Article 4.6.5.3.1) = Ultimate unit tip resistance for shafts (ksf); (See Articles 4.6.5.1.3 and 4.6.5.1.4) qIR = Ultimate unit tip resistance for shafts reduced for size effects (ksf); (See Equations 4.6.5.1.3-3 and 4.6.5.1.4-2) = Ultimate tip resistance in soil (k); (See Articles 4.6.5.1.3 and 4.6.5.1.4) QTR = Ultimate tip resistance of rock socket (k); (See Article 4.6.5.3.2) = Ultimate axial load capacity (k); (See Article 4.6.5.1) RQD = Rock Quality Designation (dim) 5,, = Incremental undrained shear strength as a function over ith depth interval (ksf); (See Article 4.6.5.1.1) 5,,, = Undrained shear strength within 2B below shaft tip (ksf); (See Article 4.6.5.1.3) W = Weight of shaft (k) = Depth to midpoint of ith interval (ft); (See Article 4.6.5.1.2) = Adhesion factor (dim) a, = Adhesion factor as a function over ith depth interval (dim); (See Article 4.6.5.1.1) = Reduction factor to estimate rock mass modulus and uniaxial strength from the modulus and =

4.6.2

79

4.6.2

HIGHWAY BRIDGES

80

uniaxial strength of intact rock (dim); (See Article 4.6.5.3.1)

3,

Load transfer factor in the ith interval (dim); (See Article 4.6.5.1.2) = Effective soil unit weight in ith interval (kcf); (See Article 4.6.5.1.2) = ith increment of shaft length (ft) = Factor to account for reduced individual capacity of closely spaced shafts in group (dim); (See Article 4.6.5.2.4.1) = Elastic shortening of shaft (ft); (See Articles 4.6.5.5.1.1 and 4.6.5.5.1.2) = Total settlement displacement at butt for shaft with rock socket (ft); (See Article 4.6.5.5.2) = Total uplift displacement at butt for shaft with rock socket (ft); (See Equation 4.6.5.5.2) = 3.1415 (dim) = Poisson’s ratio (dim) = Unconfined compressive strength of rock mass or concrete, whichever is weaker (psi); (See Article 4.6.5.3.1) = Effective vertical stress at midpoint of ith depth interval (ksf); (See Article 4.6.5.1.2) =

Az,

p.

a’.

a’,.,

The notations for dimension units include the following: dim = Dimensionless; deg = degree; ft = foot; k = kip; k/ft = kip/ft; ksf = kip/ft2; and kef = kip/ft3. The dimensional units provided with each notation are presented for illustration only to demonstrate a dimensionally correct combination of units for the shaft capacity and settlement procedures presented below. If other units are used, the dimensional correctness of the equations should be confirmed.

values used for design shall be confirmed by field and/or laboratory testing. 4.6.4.2 Measured Values Foundation stability and settlement analyses for final design shall be performed using soil and rock properties based on the results of field and/or laboratory testing. 4.6.5

Geotechnical Design

Drilled shafts shall be designed to support the design loads with adequate bearing and structural capacity, and with tolerable settlements in conformance with Articles 4.6.5 and 4.6.6. In addition, the response of drilled shafts subjected to seismic and dynamic loads, materials and shaft shall be evaluated in conformance with Articles 4.4.7.3 (dynamic ground stability) and 4.6.5.7, respec-

tively. Shaft design shall be based on working stress principles using maximum unfactored loads derived from calculations of dead and live loads from superstructures, substructures, earth (i.e., sloping ground), wind and traffic. Allowable axial and lateral loads may be determined by separate methods of analysis. The design methods presented herein for determining axial load capacity assume drilled shafts of uniform crosssection, with vertical alignment, concentric axial loading, and a relatively horizontal ground surface. The effects of an enlarged base, group action, and sloping ground are treated separately. 4.6.5.1

4.6.3

Design Terminology

Refer to Figure 4.6.3A for terminology used in design

of drilled shafts.

Axial Capacity in Soil

The ultimate axial capacity (Q~s) of drilled shafts shall be determined in accordance with the following for compression and uplift loading, respectively: QUI, =

4.6.4

Q

5 + QT

Selection of Soil and Rock Properties

Soil and rock properties defining the strength and compressibility characteristics of the foundation materials are required for drilled shaft design. 4.6.4.1

Presumptive Values

(4.6.5.1-1) —

(4.6.5.1-2) 7Qs + W O.’ The allowable or working axial load shall be deterQuii =

mined as: = Q,, 5/FS

Presumptive values for allowable bearing pressures on soil and rock may be used only for guidance, preliminary design or design of temporary structures. The use of presumptive values shall be based on the results of subsurface exploration to identify soil and rock conditions. All

W

(4.6.5.1-3)

Shafts in cohesive soils may be designed by total and

effective stress methods of analysis, for undrained and drained loading conditions, respectively. Shafts in cohesionless soils shall be designed by effective stress inethods of analysis for drained loading conditions.

4.6.5.1.1

81

DIVISION I—DESIGN ULIIMAlE AXIAL LOAD CAPA~TY (Q.~)

0.~t

SUiT

LAIERAL LOAD (P)

REJNVW~~NG SlEEL (F REQUItED)

0

513E RE3STAN4ZE (Q1)

—‘1

sOcKET DIAUEiER

I

(a)

BELL 311 USED VARIES NO LARDER ThAN 38 AS- NECESSARY~

BELL INAIAEJER (Be)

iF RESISTANtI (0,)

Orn

a. SHAFT IN SOIL

b. SHAFT IN SOIL ~¶ThROCK SOCKET

FIGURE 4.6.3A Design Terminology for Drilled Shaft Foundations 4.6.5.1.1

Side Resistance in Cohesive Soil

For shafts in cohesive soil loaded under undrained loading conditions, the ultimate side resistance may be estimated using the following:

from a consolidating clay), effective stress methods (Article 4.6.5.1.2) should be used to compute Q~ in the zone where such changes may occur. 4.6.5.1.2

Side Resistance in Cohesion less Soil

N

= itB ~ ctS,,1Az~

(4.6.5.1.1

-

I)

i=t

The ultimate unit load transfer in side resistance at any depth f,, is equal to the product of a, and s,,~ Referto Table 4.6.5.1.1 A for guidance regarding selection of a, and limiting values of f, for shafts excavated dry in open orcased holes. Environmental, long-term loading or construction factors may dictate that a depth greater than 5 feet should be ignored in estimating Q5. Refer to Figure 4.6.5.l.IA for identification of portions of drilled shaft not considered in contributing to the computed value of Q5. For

For shafts in cohesionless soil or for effective stress analysis of shafts in cohesive soils under drained loading conditions, the ultimate side resistance of axially loaded drilled shafts may be estimated using the following: N

The value of ing:

13, may be determined using the follow(4.6.5.1.2

—

2)

shafts in cohesive soil under drained loading conditions,

may be determined using the procedure in Article 4.6.5.1.2. Where time-dependent changes in soil shear strength may occur (e.g., swelling of expansive clay or downdrag Qs

The value of y~ should be determined from measurements from undisturbed samples along the length of the shaft or from empirical correlations with SPT or other insitu test methods. The ultimate unit load transfer in side

82

4.6.5.1.2

HIGHWAY BRIDGES

resistance at any depth, f,,, is equal to the product of 13, and a’,~. The limiting value of f,, for shafts in cohesionless soil is 4 ksf.

TABLE 4.6.5.l.IA Recommended Values of a and f~ for Estimation of Drilled Shaft Side Resistance in Cohesive Soil Reese and O’Neill (1988) Limiting Value of Load Value Transfer, ~ of a (ksf)

Location Along Drilled Shaft From ground surface to depth al~rng drilled shaft of 5 ft*

0

—

Bottom 1 diameter of the drilled shaft or I stem diame

0

—

4.6.5.1.3

Tip Resistance in Cohesive Soil

For axially loaded shafts in cohesive soil subjected to undrained loading conditions, the ultimate tip resistance of drilled shafts may be estimated using the following: QT

*

0.55

N,, = 6.011 + 0.2(D/B,)]; N

5.5

The depth of 5 ft may need adjustment if the drilled shaft is installed in expansive clay, or if there is substantial groundline deflection from lateral loading.

~

N~s,,,A,

(4.6.5. 1.3-1)

Values of the bearing capacity factor N~ may be determined using the following:

ter above the top of the bell (if skin fricion is being used) All other points along the sides of the drilled shaft

= qTA, =

_

9

The limiting value of unit end bearing (qT = N~s,,,) is 80 ksf. The value of s,,, should be determined from the results of in-situ and/or laboratory testing of undisturbed samples

Top Five Feet NoncontnbUtlng

Bottom One Diameter* of Stem

NoncontnbUting

Bottom

On. Diameter

Penphery of Bell Noncontnbuting

Nancontnbuting

-4-Straight Shaft

Belied Shaft

Two Diameters in StIff Fissured Clay. FIGURE 4.6.5.1.lA

(4.6.5.1.3-2)

Identification of Portions of Drilled Shafts Neglected for Estimation of Drilled Shaft Side Resistance in Cohesive Soil Reese and O’Neill (1988)

4.6.5.1.3

obtained within a depth of 2B below the tip of the shaft. If the soil within 2B of the tip is of soft consistency, the value of N~ should be reduced by one-third. IfB, > 6.25 feet (75 inches) and shaft settlements will

not be evaluated, the value of q.~. should be reduced to qTR as follows: qTR =

(2.5/[aB,/12 + 2.5b])qT

FrqT =

a

= 0.0071 + 0.0021(D/B,); a =0.015

b

= 0.45(s,,,Y’

5; 0.5 = b = 1.5

(4.6.5.1.3-3) (4.6.5.1.3-4) (4.6.5.1.3-5)

The limiting value of qTR is 80 ksf. For shafts in cohesive soil under drained loading conditions, QT may be estimated using the procedure described in Article 4.6.5.1.4. 4.6.5.1.4

Tip Resistance in Cohesionless Soil

For axially loaded drilled shafts in cohesionless soils or for effective stress analysis of axially loaded drilled shafts in cohesive soil, the ultimate tip resistance may be estimated using the following: QT =

qTAI

(4.6.5.1.4-1)

The value of qT may be determined from the results of standard penetration testing using uncorrected blow count readings within a depth of 2B below the tip of the shaft. Refer to Table 4.6.5.1 .4A for recommended values of q.r. If B,> 4.2 feet (50 inches) and shaft settlements will not be evaluated, the value of q~ should be reduced to qTR as follows: qTR =

4.6.5.2 4.6.5.2.1

83

DIVISION I—DESIGN

(50/12B,)qT

(4.6.5.1.4-2) Factors Affecting Axial Capacity in Soil Soil Layering and Variable Soil Strength with Depth

The design of shafts in layered soil deposits or soil deposits having variable strength with depth requires evaluation of soil parameters characteristic of the respective layers ordepths. Q~ in such soil deposits may be estimated by dividing the shaft into layers according to soil type and properties, determining Q 5 for each layer, and summing values for each layer to obtain the total Qs. If the soil below the shaft tip is of variable consistency, QT may be estimated using the predominant soil strata within 2B below the shaft tip. For shafts extending through soft compressible layers to tip bearing on firm soil or rock, consideration shall be

TABLE 4.6.5.l.4A Recommended Values of qT* for Estimation of Drilled Shaft Tip Resistance in Cohesionless Soil after Reese and O’Neill (1988) Standard Penetration Resistance N (Blows/Foot) (uncorrected) 0to75 Above 75

Value of qT (ksf) l.20N 90

~Ultimatevalue or value at settlement of 5 percent of base diameter.

given to the effects of negative skin friction (Article 4.6.5.2.5) due to the consolidation settlement of soils sur-

rounding the shaft. Where the shaft tip would bear on a thin firm soil layer underlain by a softer soil unit, the shaft shall be extended through the softer soil unit to eliminate the potential for a punching shear failure into the softer deposit. 4.6.5.2.2

Ground Water

The highest anticipated water level shall be used for design. 4.6.5.2.3

Enlarged Bases

An enlarged base (bell or underream) may be used at the shaft tip in stiff cohesive soil to increase the tip bearing area and reduce the unit end bearing pressure, or to provide additional resistance to uplift loads. The tip capacity of an enlarged base shall be determined assuming that the entire base area ts effective in transferring load. Allowance of full effectiveness of the enlarged base shall be permitted only when cleaning of the bottom of the drilled hole is specified and can be acceptably completed before concrete placement. 4.6.5.2.4

Group Action

Evaluation of group shaft capacity assumes the effects of negative skin friction (if any) are negligible. 4.6.5.2.4.1

Cohesive Soil

Evaluation of group capacity of shafts in cohesive soil shall consider the presence and contact of a cap with the ground surface and the spacing between adjacent shafts. For a shaft group with a cap in firm contact with the ground, Q,,5 may be computed as the lesser of (I) the sum of the individual capacities of each shaft in the group or (2) the capacity of an equivalent pier defined in the perimeter area of the group. For the equivalent pier, the

84

4.6.5.2.4.1

HIGHWAY BRIDGES

shear strength of soil shall not be reduced by any factor (e.g., a1) to determine the Q~ component of Q,,1,, the total base area of the equivalent pier shall be used to determine the QT component of Q,,,, and the additional capacity of the cap shall be ignored. If the cap is not in firm contact with the ground, or if the soil at the surface is loose or soft, the individual capacity of each shaft should be reduced to ~ times QT for an isolated shaft, where ~ = 0.67 for a center-to-center (CTC) spacing of 3B and ~ = 1.0 for a CTC spacing of 6B. For intermediate spacings, the value of ~ may be determined by linear interpolation. The group capacity may then be computed as the lesser of (I) the sum of the modified individual capacities of each shaft in the group, or (2) the capacity of an equivalent pier as described above. 4.6.5.2.4.2

Cohesionless Soil

Evaluation of group capacity of shafts in cohesionless soil shall consider the spacing between adjacent shafts. Regardless of cap contact with the ground, the individual capacity of each shaft should be reduced to ~times QT for an isolated shaft, where ~ = 0.67 for a center-to-center (CTC) spacing of 3B and ~ = 1.0 for a CTC spacing of 8B. For intermediate spacings, the value of ~ may be determined by linear interpolation. The group capacity may be computed as the lesser of (I) the sum of the modified individual capacities of each shaft in the group or (2) the capacity of an equivalent pier circumscribing the group, including resistance over the entire perimeter and base areas. 4.6.5.2.4.3

Group in Strong Soil Overlying Weaker Soil

If a group of shafts is embedded in a strong soil deposit which overlies a weaker deposit (cohesionless and cohesive soil), consideration shall be given to the potential for a punching failure of the tip into the weaker soil strata. For this case, the unit tip capacity of the equivalent shaft (q~) may be determined using the following: qE = qLo +

(HIl0B,)(q51~

—

q~0) = q,~

(4.6.5.2.4.3-1)

If the underlying soil unit is a weaker cohesive soil strata, careful consideration shall be given to the potential for large settlements in the weaker layer. 4.6.5.2.5

Vertical Ground Movement

The potential for external loading on a shaft by vertical ground movement (i.e., negative skin friction/downdrag due to settlement of compressible soil or uplift due to heave of expansive soil) shall be considered as a part of

design. For design purposes, it shall be assumed that the full magnitude of maximum potential vertical ground movement occurs. Evaluation of negative skin friction shall include a load-transfer method of analysis to determine the neutral point (i.e., point of zero relative displacement) and load distribution along shaft (e.g., Reese and O’Neill, 1988). Due to the possible time dependence associated with vertical ground movement, the analysis shall consider the effed of time on load transfer between the ground and shaft and the analysis shall be performed for the time period relating to the maximum axial load transfer to the shaft. Shafts designed for and constructed in expansive soil shall extend to a sufficient depth into moisture-stable soils to provide adequate anchorage to resist uplift movement. In addition, sufficient clearance shall be provided between the ground surface and underside of caps or beams connecting shafts to preclude the application of uplift loads at the shaft/cap connection from swelling ground conditions. Uplift capacity shall rely only on side resistance in conformance with Article 4.6.5.1. If the shaft has an enlarged base, Q5 shall be determined in conformance with Article

4.6.5.2.3.

4.6.5.2.6

Method of Construction

The load capacity and deformation behavior of drilled shafts can be greatly affected by the quality and method(s) of construction. The effects of construction methods are incorporated in design by application of a factor of safety consistent with the expected construction method(s) and level of field quality control measures (Article 4.6.5.4). Where the spacing between shafts in a group is restricted, consideration shall be given to the sequence of construction to minimize the effect of adjacent shaft construction operations on recently constructed shafts. 4.6.5.3

Axial Capacity in Rock

Drilled shafts are socketed into rock to limit axial displacements, increase load capacity and/or provide fixity for resistance to lateral loading. In determining the axial capacity of drilled shafts with rock sockets, the side resistance from overlying soil deposits may be ignored. Typically, axial compression load is carried solely by the side resistance on a shaft socketed into rock until a total shaft settlement (ps) on the order of 0.4 inches occurs. At this displacement, the ultimate side resistance, QSR, is mobilized and slip occurs between the concrete and rock. As a result of this slip, any additional load is transferred to the tip. The design procedures assume the socket is constructed in reasonably sound rock that is little affected by

4.6.5.3

85

DIVISION I—DESIGN

construction (i.e., does not rapidly degrade upon excavation and/or exposure to air or water) and which is cleaned prior to concrete placement (i.e., free of soil and other debris). If the rock is degradable, consideration of special construction procedures, larger socket dimensions, or reduced socket capacities should be considered. 4.6.5.3.1

4.6.5.3.2

Tip Resistance

Evaluation of ultimate tip resistance (QTR) for rocksocketed drilled shafts shall consider the influence of rock discontinuities. QTR for rock-socketed drilled shafts may be determined using the following: QTR =

Side Resistance

The ultimate side resistance (QSR) for shafts socketed into rock may be determined using the following: QSR =

‘TTBrDr(0.l44qsR)

(4.6.5.3.1-I)

Refer to Figure 4.6.5.3.1 A for values of q,,~. For uplift loading Q,,’, of a rock socket shall be limited to O.7QSR. The design of rock sockets shall be based on the unconfined compressive strength of the rock mass (C,,,) or concrete, whichever is weaker (a’~). C,,, may be estimated using the following relationship: Cm =

Nm~CoAi

(4.6.5.3.2-I)

Preferably, values of C 0 should be determined from the results of laboratory testing of rock cores obtained within 2B of the base of the footing. Where rock strata within this interval are variable in strength, the rock with the lowest capacity should be used to determine QTR. Alternatively, Table 4.4.8.l.2B may be used as a guide to estimate C,,. For rocks defined by very poor quality, the value of QTR cannot be less than the value of QT for an equivalent soil mass. 4.6.5.3.3

Factors Affecting Axial Capacity in Rock

(4.6.5.3.1-2)

aECO

4.6.5.3.3.1

Refer to Article 4.4.8.2.2 for the procedure to determine uF as a function of RQD.

Rock Stratification

Rock stratification shall be considered in the design of rock sockets as follows:

in

0.

0’ ILl

C,

z 4

I— in

bJ ci:

w a i~i I”

z I— La

V

0

in 0

0

‘r 20 200

500

1000

2000

5000

10,000

20.000

UNCONFINED COMPRESSIVE STRENGTh OF ROCK OR CONCRETE. WHICHEVER IS WEAKER.Gc(psi)

FIGURE 4.6.5.3.IA Procedure for Estimating Average Unit Shear for Smooth Wall Rock-Socketed Shafts Horvath, et al. (1983)

4.6.5.3.3.1

HIGHWAY BRIDGES

86

• Sockets embedded in alternating layers of weak and strong rock shall be designed using the strength of the weaker rock. • The side resistance provided by soft or weathered rock should be neglected in determining the required socket length where a socket extends into more competent underlying rock. Rock is defined as soft when the uniaxial compressive strength of the weaker rock is less than 20 percent of that of the stronger rock, or weathered when the RQD is less than 20 percent. • Where the tip of a shaft would bear on thin rigid rock strata underlain by a weaker unit, the shaft shall be extended into or through the weaker unit (depending on load capacity or deformation requirements) to eliminate the potential for failure due to flexural tension or punching failure of the thin rigid stratum. • Shafts designed to bear on strata in which the rock surface is inclined should extend to a sufficient depth to ensure that the shaft tip is fully bearing on the rock. • Shafts designed to bear on rock strata in which bedding planes are not perpendicular to the shaft axis shall extend a minimum depth of 2B into the dipping strata to minimize the potential for shear failure along natural bedding planes and other slippage surfaces associated with stratification. 4.6.5.3.3.2

Rock Mass Discontinuities

The strength and compressibility of rock will be affected by the presence of discontinuities (joints and fractures). The influence of discontinuities on shaft behavior will be dependent on their attitude, frequency and condition, and shall be evaluated on a case-by-case basis as necessary. 4.6.5.3.3.3

Method of Construction

The effect of the method of construction on the engineering properties of the rock and the contact between the rock and shaft shall be considered as a part of the design process.

4.6.5.4 Factors of Safety Drilled shafts in soil or socketed in rock shall be designed for a minimum factor of safety of 2.0 against bearing capacity failure (end bearing, side resistance or combined) when the design is based on the results of a load test conducted at the site. Otherwise, shafts shall be designed for a minimum factor of safety 2.5. The minimum recommended factors of safety are based on an assumed normal level of field quality control during shaft construction. If a

4.6.5.5

Deformation of Axially Loaded Shafts

The settlement of axially loaded shafts at working or allowable loads shall be estimated using elastic or load transfer analysis methods. For most cases, elastic analysis will be applicable for design provided the stress levels in the shaft are moderate relative to Q,,,,. Where stress levels are high, consideration should be given to methods of load transfer analysis. 4.6.5.5.1

Shafts in Soil

Settlements should be estimated for the design or working load. 4.6.5.5.1.1

Cohesive Soil

The short-term settlement of shafts in cohesive soil may be estimated using Figures 4.6.5.5.l.IA and 4.6.5.5.1.1 B. The curves presented indicate the proportions of the ultimate side resistance (Qs) and ultimate tip resistance (QT) mobilized at various magnitudes of settlement. The total axial load on the shaft (Q) is equal to the sum of the mobilized side resistance (Qs) and mobilized tip resistance (Q,). The settlement in Figure 4.6.5.5.1.1 A incorporates the effects of elastic shortening of the shaft provided the shaft is of typical length (i.e., D < 100 ft). For longer shafts, the effects of elastic shortening may be estimated using the following: p. = PD/AEC

(4.6.5.5.1. 1-1)

For a shaft with an enlarged base in cohesive soil, the diameter of the shaft at the base (Bb) should be used in Figure 4.6.5.5.I.lB to estimate shaft settlement at the tip. Refer to Article 4.4.7.2.3 for procedures to estimate the consolidation settlement component for shafts extending into cohesive soil deposits. 4.6.5.5.1.2

Cohesionless Soil

The short-term settlement of shafts in cohesionless soil may be estimated using Figures 4.6.5.5.l.2A and 4.6.5.5.l.2B. The curves presented indicate the proportions of the ultimate side resistance (Q~) and ultimate tip resistance (QT) mobilized at various magnitudes of settlement. The total axial load on the shaft (Q) is equal to the sum of the mobilized side resistance (Qs) and mobilized tip resistance (Q,). Elastic shortening of the shaft shall be estimated using the following relationship:

normal level of field quality control cannot be assured,

higher minimum factors of safety shall be used.

Pe

=

PD/AE~

(4.6.5.5.1.2~~I)

4.6.5.5.1.2

87

DIVISION I—DESIGN

1.2

S in

C U U IC ‘0 (U I-

0.I

S

0.6

~1 U,

0 C C.

E

5

C—

w a 0.4

—

Range at R•aulta

——

Tr•nd Ufie

Rang. of Remits — — —

Trend Un•

0.2

0.0 0.0 0.2

0.4

0.8 0.6

1.0

1.2

1.4

1.6

1.8

2.0

Settlement

0

1

Diameter of Shaft

FIGURE 4.6.5.5.l.lA Load Transfer in Side Resistance Versus Settlement Drilled Shafts in Cohesive Soil After Reese and O’Neill (1988)

2

3 4 5 5 7 Settlement of Base Diameter of Base

8

9

10

FIGURE 4.6.5.5.l.lB Load Transfer in Tip Bearing Settlement Drilled Shafts in Cohesive Soil

After Reese and O’Neill (1988) 4.6.5.5.1.3

Mixed Soil Profile

The short-term settlement of shafts in a mixed soil profile may be estimated by summing the proportional settlement components from layers of cohesive and cohesionless soil comprising the subsurface profile. 4.6.5.5.2

Shafts Socketed into Rock’

In estimating the displacement of rock-socketed drilled shafts, the resistance to deformation provided by overlying soil deposits may be ignored. Otherwise, the load transfer to soil as a function of displacement may be estimated in accordance with Article 4.6.5.5.1. The butt settlement (pj of drilled shafts fully socketed into rock may be determined using the following which is modified to include elastic shortening of the shaft:

= Q,,[(Ip,,/BrE,,,) + (D/AEJ]

Refer to Figure 4.6.5.5.2B to determine I,,,. The rock mass modulus (E,,,) should be determined based on the results of in-situ testing (e.g., pressure-meter) or estimated from the results of laboratory tests in which E,, is the modulus of intact rock specimens, and (E,,) is estimated in accordance with Article 4.4.8.2.2. For preliminary design or when site-specific test data cannot be obtained, guidelines for estimating values of E,,, such as presented in Table 4.4.8.2.2B or Figure 4.4.8.2.2A, may be used. For preliminary analyses or for final design when in-situ test results are not available, a value of av = 0.15 should be used to estimate E,,,.

4.6.5.5.3 = Q[(Ip,,/BrEm) +

(Dr/AEc)]

(4.6.5.5.21)

Refer to Figure 4.6.5.5.2A to determine ~ The uplift displacement (p,,) at the butt of drilled shafts fully socketed into rock may be determined using the following which is modified to include elastic shortening of the shaft:

(4.6.5.5.22)

Tolerable Movement

Tolerable axial displacement criteria for drilled shaft foundations shall be developed by the structural designer consistent with the function and type of structure, fixity of bearings, anticipated service life, and consequences of unacceptable displacements on the structure performance. Drilled shaft displacement analyses shall be based on the results of in-situ and/or laboratory testing to characterize

88

4.6.5.5.3

HIGHWAY BRIDGES 2.0

t2~

1.8

to I

1.6

I0

‘S

‘I A

0 (U U ‘S 0 (U S

AS

C

Range of Remits for OeflecIon—Softs~ng Response

w

wC U (U —

Range of Reajis for Oeflecuon—f4ardeftng Response

Range of Remus Trend Line

0.2 Trend Line 0.0

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

the load-deformation behavior of the foundation materials. Refer to Article 4.4.7.2.5 for additional guidance regarding tolerable vertical and horizontal movement criteria. 4.6.5.6

Lateral Loading

The design of laterally loaded drilled shafts shall account for the effects of soillrock-structure interaction between the shaft and ground (e.g., Reese, 1984; Borden and Gabr, 1987). Methods of analysis evaluating the ultimate capacity or deflection of laterally loaded shafts (e.g., Broms, I 964a,b; Singh, et al., 1971) may be used for preliminary design only as a means to determine approximate shaft dimensions. 4.6.5.6.1 4.6.5.6.1.1

Factors Affecting Laterally’ Loaded Shafts Soil Layering

The design of laterally loaded drilled shafts in layered soils shall be based on evaluation of the soil parameters characteristic of the respective layers. 4.6.5.6.1.2

Ground Water

The highest anticipated water level shall be used for design.

11

12

Settlement of Base Diameter of Base

Diameter of Shaft

FIGURE 4.6.S.S.I.2A Load Transfer in Side Resistance Versus Settlement Drilled Shafts in Cohesionless Soil After Reese and O’Neill (1988)

10

12345678

Settlement

FIGURE 4.6.5.5.l.2B

Load Transfer in

Tip Bearing Versus Settlement Drilled Shafts in Cohesionless Soil

After Reese and O’Neill (1988) 4.6.5.6.1.3

Scour

The potential for loss of lateral capacity due to scour shall be considered in the design. Refer to Article 1.3.2 and FHWA (1988) for general guidance regarding hydraulic studies and design. If heavy scour is expected, consideration shall be given to designing the portion of the shaft that would be exposed as a column. In all cases, the shaft length shall be determined such that the design structural load can be safely supported entirely below the probable scour depth. 4.6.5.6.1.4

Group Action

There is no reliable rational method for evaluating the group action for closely spaced, laterally loaded shafts. Therefore, as a general guide, drilled shafts in a group may be considered to act individually when the center-to-center (CTC) spacing is greater than 2.SB tn the direction normal to loading, and CTC > 8B in the direction parallel to loading. For shaft layouts not conforming to these criteria, the effects of shaft interaction shall be considered in the design. As a general guide, the effects of group action for in-line CTC < 8B may be considered using the ratios (CGS, 1985) appearing on page 89.

4.6.5.6.1.4

89

DIVISION I—DESIGN 10

I

0’9 0’8 0’7

I

I

I

I

I

I

I 6

I 7

8

cc

0~6 0’S

Em

~0r cc

1’0 2

Ec

Gap

•0’2

03

( 02

-/

—l -1 05

‘pa

0’l

cog 0’06 007 0’06

0

I

2

3

II 4

I ~

9

FIGURE 4.6.5.5.2B Influence Coefficient for Elastic Uplift Displacement of Rock-Socketed Drilled Shafts Modified after Pells and Turner (1979) 0r’8r

4.6.5.6.1.7

FIGURE 4.6.5.5.2A Influence Coefficient for Elastic Settlement of Rock.Socketed Drilled Shafts Modified after Pells and Turner (1979)

CTC Shaft Spacing for In-line Loading 8B 6B 4B 3B 4.6.5.6.1.5

Ratio of Lateral Resistance of Shaft in Group to Single Shaft 1.00 0.70 0.40

0.25

Cyclic Loading

The effects of traffic, wind, and other nonseismic cyclic loading on the load-deformation behavior of laterally loaded drilled shafts shall be considered during design. Analysis of drilled shafts subjected to cyclic loading may be considered in the C0M624 analysis (Reese, 1984). 4.6.5.6.1.6

CombinedAxial and Lateral Loading

The effects of lateral loading in combination with axial loading shall be considered in the design. Analysis of drilled shafts subjected to combined loading may be considered in the C0M624 analysis (Reese, 1984).

Sloping Ground

For drilled shafts which extend through or below

sloping ground, the potential for additional lateral loading shall be considered in the design. The general method of analysis developed by Borden and Gabr (1987) may be used for the analysis of shafts in stable slopes. For shafts in marginally stable slopes, additional consideration should be given for low factors of safety against slope failure or slopes showing ground creep, or when shafts extend through fills overlying soft foundation soils and bear into more competent underlying soil or rock formations. For unstable ground, detailed explorations, testing and analysis are required to evaluate potential additional lateral loads due to slope movements. 4.6.5.6.2

Tolerable Lateral Movements

Tolerable lateral displacement criteria for drilled shaft foundations shall be developed by the structural designer consistent with the function and type of structure, fixity of bearings, anticipated service life, and consequences of unacceptable displacements on the structure performance. Drilled shaft lateral displacement analysis shall be based on the results of in-situ and/or laboratory testing to characterize the load-deformation behavior of the foundation materials.

90

4.6.5.6.7

HIGHWAY BRIDGES

4.6.5.7

Dynamic/Seismic Design

Refer to Division I-A—Seismic Design and Lam and Martin (I 986a; I986b) for guidance regarding the design of drilled shafts subjected to dynamic and seismic loads. 4.6.6

Structural Design and General Shaft Dimensions

4.6.6.1

General

Drilled shafts shall be designed to insure that the shaft will not collapse or suffer loss of serviceability due to excesstve stress and/or deformation. Shafts shall be designed to resist failure following applicable procedures presented in Section 8. All shafts should be sized in 6-inch increments with a minimum shaft diameter of 18 inches. The diameter of shafts with rock sockets should be sized a minimum of 6 inches larger than the diameter of the socket. The diameter of columns supported by shafts shall be less than or equal to B. 4.6.6.2

Reinforcement

Where the potential for lateral loading is insignificant, drilled shafts need to be reinforced for axial loads only. Those portions of drilled shafts that are not supported laterally shall be designed as reinforced concrete columns in accordance with Articles 8.15.4 and 8.16.4, and the reinforcing steel shall extend a minimum of 10 feet below the plane where the soil provides adequate lateral restraint. Where permanent steel casing is used and the shell is smooth pipe and more than 0.12 inch in thickness, it may be considered as load carrying in the absence of corrosion. The design of longitudinal and spiral reinforcement shall be in conformance with the requirements of Articles 8.18.1 and 8.18.2.2, respectively. Development of deformed reinforcement shall be in conformance with the requirements of Articles 8.24, 8.26, and 8.27.

4.6.6.2.1

Longitudinal Bar Spacing

The minimum clear distance between longitudinal reinforcement shall not be less than 3 times the bar diameter nor 3 times the maximum aggregate size. If bars are bundled in forming the reinforcing cage, the minimum

clear distance between longitudinal reinforcement shall not be less than 3 times the diameterof the bundled bars. Where heavy reinforcement is required, consideration may be given to an inner and outer reinforcing cage. 4.6.6.2.2

Splices

Splices shall develop the full capacity of the bar in tension and compression. The location of splices shall be staggered around the perimeter of the reinforcing cage so as not to occur at the same horizontal plane. Splices may be developed by lapping, welding, and special approved connectors. Splices shall be in conformance with the requirements of Article 8.32. 4.6.6.2.3

Transverse Reinforcement

Transverse reinforcement shall be designed to resist stresses caused by fresh concrete flowing from inside the cage to the side of the excavated hole. Transverse reinforcement may be constructed of hoops or spiral steel. 4.6.6.2.4

Handling Stresses

Reinforcement cages shall be designed to resist handling and placement stresses. 4.6.6.2.5

Reinforcement Cover

The reinforcement shall be placed a clear distance of not less than 2 inches from the permanently cased or 3 inches from the uncased sides. When shafts are constructed in corrosive or marine environments, or when concrete is placed by the water or slurry displacement methods, the clear distance shall not be less than 4 inches for uncased shafts and shafts with permanent casings not sufficiently corrosion resistant. The reinforcement cage shall be centered in the hole using centering devices. All steel centering devices shall be epoxy coated. 4.6.6.2.6

Reinforcement into Superstructure

Sufficient reinforcement shall be provided at the junction of the shaft with the superstructure to make a suitable connection. The embedment of the reinforcement into the cap shall be in conformance with Articles 8.24 and 8.25. 4.6.6.3

Enlarged Bases

Enlarged bases shall be designed to insure that plain concrete is not overstressed. The enlarged base shall slope at a side angle not less than 30 degrees from the vertical and have a bottom diameter not greater than 3 times the

4.6.6.3

diameter of the shaft. The thickness of the bottom edge of the enlarged base shall not be less than 6 inches. 4.6.6.4

Center-to-Center Shaft Spacing

The center-to-center spacing ofdrilled shafts should be 3B or greater to avoid interference between adjacent shafts during construction. If closer spacing is required, the sequence of construction shall be specified and the interaction effects between adjacent shafts shall be evaluated by the designer. 4.6.7

91

DIVISION I—DESIGN

Load Testing

4.6.7.1

General

Where necessary, a full scale load test (or tests) should be conducted on a drilled shaft foundation(s) to confirm response to load. Load tests shall be conducted using a test shaft(s) constructed in a manner and of dimensions and materials identical to those planned for the production shafts into the materials planned for support. Load testing should be conducted whenever special site conditions or combinations of load are encountered, or when structures of special design or sensitivity (e.g., large bridges) are to be supported on drilled shaft foundations. 4.6.7.2

Load Testing Procedures

Load tests shall be conducted following prescribed written procedures which have been developed from accepted standards (e.g., ASTM, 1989; Crowther, 1988) and modified, as appropriate, for the conditions at the site. Standard pile load testing procedures developed by the American Society for Testing and Materials which may be modified for testing drilled shafts include:

• Apparatus for measuring movements. • Apparatus for measuring loads. • Procedures for loading including rates of load application, load cycling and maximum load. • Procedures for measuring movements. • Safety requirements. • Data presentation requirements and methods of data analysis. • Drawings showing the procedures and materials to be used to construct the load test apparatus. As a minimum, the results of the load test(s) shall provide the load-deformation responseat the butt of the shaft. When appropriate, information concerning ultimate load capacity, load transfer, lateral load-displacement with depth, the effects of shaft group interaction, the degree of fixity provided by caps and footings, and other data pertinent to the anticipated loading conditions on the production shafts shall be obtained. 4.6.7.3

Selection of an appropriate load test method shall be based on an evaluation of the anticipated types and duration of loads during service, and shall include consideration of the following: • The immediate goals of the load test (i.e., to proof load the foundation and verify design capacity). • The loads expected to act on the production foundation (compressive and/or uplift, dead and/or live), and the soil conditions predominant in the region of concern. • The local practice or traditional method used in similar soil/rock deposits. • Time and budget constraints.

• ASTM D 1143, Standard Method of Testing Piles Under Static Axial Compressive Load; • ASTM D 3689, Standard Method of Testing Individual Piles Under Static Axial Tensile Load; and • ASTM D 3966, Standard Method for Testing Piles Under Lateral Loads. A simplified procedure for testing drilled shafts permitting determination of the relative contribution of side resistance and tip resistance to overall shaft capacity is also available (Osterberg, 1984). As a minimum, the written test procedures should include the following: • Apparatus for applying loads including reaction system and loading system.

Load Test Method Selection

Part C STRENGTH DESIGN METHOD LOAD FACTOR DESIGN Note to User: Article Number 4.7 has been omitted inten tionally.

4.8

SCOPE

Provisions of this section shall apply for the design of spread footings, driven piles, and drilled shaft foundations.

92

4.9

HIGHWAY BRIDGES

4.9 DEFINITIONS Batter Pile—A pile driven at an angle inclined to the vertical to provide higher resistance to lateral loads. Combination End-Bearing and Friction Pile—Pile that derives its capacity from the contributions of both end bearing developed at the pile tip and resistance mobilized along the embedded shaft. Deep Foundation—A foundation which derives its support by transferring loads to soil or rock at some depth below the structure by end bearing, by adhesion or friction or both. Design Load—All applicable loads and forces or their related internal moments and forces used to proportion a foundation. In load factor design, design load refers to nominal loads multiplied by appropriate load factors. Design Strength—The maximum load-carrying capacity of the foundation, as defined by a particular limit state. In load factor design, design strength is computed as the product of the nominal resistance and the appropriate performance factor. Drilled Shaft—A deep foundation unit, wholly or parlly embedded in the ground, constructed by placing fresh concrete in a drilled hole with or without steel reinforcement. Drilled shafts derive their capacities from the surrounding soil and/or from the soil or rock strata below their tips. Drilled shafts are also commonly referred to as caissons, drilled caissons, bored piles or drilled piers. End-Bearing Pile—A pile whose support capacity is derived principally from the resistance of the foundation material on which the pile tip rests. Factored Load—Load, multiplied by appropriate load factors, used to proportion a foundation in load factor design. Friction Pile—A pile whose support capacity is derived principally from soil resistance mobilized along the side of the embedded pile. Limit State—A limiting condition in which the foundation and/or the structure it supports are deemed to be unsafe (i.e., slrength limit state), or to be no longer fully useful for their intended function (i.e., serviceability limit state). Load Effect—The force in a foundation system (e.g., axial force, sliding force, bending moment, etc.) due to the applied loads. Load Factor—A factor used to modify a nominal load effect, which accounts for the uncertainties associated with the determination and variability of the load effect. Load Factor Design—A design method in which safety provisions are incorporated by separately accounting for uncertainties relative to load and resistance. Nominal Load—A typical value or a code-specified value for a load.

Nominal Resistance—The analytically estimated loadcarrying capacity of a foundation calculated using nominal dimensions and material properties, and established soil mechanics principles. Performance Factor—A factor used to modify a nominal resistance, which accounts for the uncertainties associated with the determination of the nominal resistance and the variability of the actual capacity. Pile—A relatively slender deep foundation unit. wholly or partly embedded in the ground, installed by driving, drilling. augering,jetting, or otherwise. and which derives its capacity from the surrounding soil and/or from the soil or rock strata below its tip. Piping—Progressive erosion of soil by seeping water, producing an open pipe through the soil, through which water flows in an uncontrolled and dangerous manner. Shallow Foundation—A foundation which derives its support by transferring load directly to the soil or rock at shallow depth. If a single slab covers the supporting stratum beneath the entire area of the superstructure. the foundation is known as a combined footing. If various parts of the structure are supported individually, the individual supports are known as spread footings, and the foundation is called a footing foundation. 4.10

4.10.1

LIMIT STATES, LOAD FACTORS, AND RESISTANCE FACTORS

General

All relevant limit states shall be considered in the design to ensure an adequate degree of satety and serviceability. 4.10.2

Serviceability Limit States

Service limit states for foundation design shall include: —settlements, and —lateral displacements. The limit state for settlement shall be based upon rideability and economy. The cost of limiting foundation movements shall be compared to the cost of designing the superstructure so that it can tolerate larger movements, or of correcting the consequences of movements through maintenance, to determine minimum lifetinte cost. More stringent criteria may be established by the owner. 4.10.3

Strength Limit St.ates

Strength limit states for foundation design shall include:

4.10.3

DIVISION I—DESIGN

—bearing resistance failure, —excessive loss of contact, —sliding at the base of footing, —loss of overall stability, and —structural capacity. Foundations shall be proportioned such that the factored resistance is not less than the effects of factored loads specified in Section 3.

4.10.4

Strength Requirement

Foundations shall be proportioned by the methods specified in Articles 4.11 through 4.13 so that their design strengths are at least equal to the required strengths. The required strength is the combined effect of the factored loads for each applicable load combination stipulated in Article 3.22. The design strength is calculated for each applicable limit state as the nominal resistance, R,,, multiplied by an appropriate performance (or resistance) factor, 4). Methods for calculating nominal resistance are provided in Articles 4. II through 4.13, and values of performance factors are given in Article 4.10.6.

4.10.5

Load Combinations and Load Factors

Foundations shall be proportioned to withstand safely all load combinations stipulated in Article 3.22 which are applicable to the particular site or foundation type. With the exception of the portions of concrete or steel piles that are above the ground line and are rigidly connected to the superstructure as in rigid frame or continuous structures, impact forces shall not be considered in foundation design. (See Article 3.8.1.) Values of ~yand 13 coefficients for load factor design, as given in Table 3.22.1 A. shall apply to strength limit state considerations: while those for service load design (also given in Table 3.22.IA) shall apply to serviceability considerations.

4.11

93

SPREAD FOOTINGS

4.11.1 General Considerations 4.11.1.1

General

Provisions of this Article shall apply to design of isolated footings, and where applicable, to combined footings. Special attention shall be given to footings on fill. Footings shall be designed to keep the soil pressure as nearly uniform as practicable. The distribution of soil pressure shall be consistent with properties of the soil and the structure, and with established principles of soil mechanics. 4.11.1.2

Depth

The depth of footings shall be determined with respect to the character of the foundation materials and the possibility of undermining. Footings at stream crossings shall be founded at depth below the maximum anticipated depth of scour as specified in Article 4.11.1.3. Footings not exposed to the action of stream current shall be founded on a firm foundation and below frost level. Consideration shall be given to the use of either a geotextile or graded granular filter layer to reduce susceptibility to piping in rip rap or abutment backfill. 4.11.1.3

Scour Protection

Footings supported on soil or degradable rock strata shall be embedded below the maximum computed scour depth or protected with a scour counter-measure. Footings supported on massive, competent rock formations which are highly resistant to scour shall be placed directly’ on the cleaned rock surface. Where required, additional lateral resistance shall be provided by drilling and grouting steel dowels into the rock surface rather than blasting to embed the footing below the rock surface. 4.11.1.4 Frost Action

4.10.6

Performance Factors

Values of performance factors for different types of foundation systems at strength limit states shall be as specified in Tables 4.10.6-1,4.10.6-2, and 4.10.6-3, unless regionally specific values are available. If methods other than those given in Tables 4.10.6-I. 4.10.6-2, and 4.10.6-3 are used to estimate the soil capacity, the performance factors chosen shall provide the same reliability as those given in these tables.

In regions where freezing of the ground occurs during the winter months, footings shall be founded below the maximum depth of frost penetration in order to prevent damage from frost heave.

4.11.1.5

Anchorage

Footings which are founded on inclined smooth solid rock surfaces and which are not restrained by an overburden of resistant material shall be effectively anchored by

94

4. 11.1.5

HIGHWAY BRIDGES

TABLE 4.10.6-1

Performance Factors for Strength Limit States for Shallow Foundations Performance Factor (~)

T~,pe of Limit State 1. Bearing capacity a. Sand

—Semi-empirical procedure using SPT data —Semi-empirical procedure using CPT data —Rational method— using 4~ estimated from SPT data using ~f estimated from CPT data b. Clay —Semi-empirical procedure using CPT data —Rational method using shear strength measured in lab tests using shear strength measured in field vane tests using shear strength estimated from CPT data c. Rock —Semi-empirical procedure (Carter and Kulbawy) 2. Sliding Sliding on clay is controlled by the strength of the clay when the clay shear strength is less than times the normal stress, and is controlled by the normal stress when the clay shear strength is greater than 0.5 times the normal stress.

0.45

0.55 0.35 0.45

0.50 0.60 0.60 0.50 0.60

0.5

a. Precast concrete placed on sand using ~ estimated from SPT data 4~t estimated from CPT data using

0.90 0.90

b. Concrete cast in place on sand using ~t estimated from SPT data using ~ estimated from CPT data c. Clay (where shear strength is less than 0.5 times normal pressure) using shear strength measured in lab tests using shear strength measured in field tests using shear strength estimated from CPT data d. Clay (where the strength is greater than 0.5 times normal pressure)

where

0.85 0.85 0.80 0.85

4~ = frictional angle of sand, SPT = Standard Penetration Test, CPT = Cone Penetration Test.

means of rock anchors, rock bolts, dowels, keys or other suitable means. Shallow keying of large footing areas shall be avoided where blasting is required for rock removal. 4.11.1.6

0.80 0.80

4.11.1.7

Uplift

Where foundations may be subjected to uplift forces, they shall be investigated both for resistance to pullout and for their structural strength.

Groundwater 4.11.1.8

Footings shall be designed for the highest anticipated position of the groundwater table. The influence of the groundwater table on bearing capacity of soils or rocks, and settlements of the structure shall be considered. In cases where seepage forces are present, they should also be included in the analyses.

Deterioration

Deterioration of the concrete in a foundation by sulfate, chloride, and acid attack should be investigated. Laboratory testing of soil and groundwater samples for sulfates, chloride and pH should be sufl’icient to assess deterioration potential. When chemical wastes are suspected, a more thorough chemical anal-

4.11.1.8

DIVISION

TABLE 4.10.6-2

I—DESIGN

95

Perfonnance Factors for Geotechnical Strength Limit States in Axially Loaded Piles Performance Factor

Method/SoillCondition Ultimate bearing capacity of single piles

Skin friction

a-method 13-method X-method

0.70 0.50 0.55

End bearing

Clay (Skempton, 1951) Sand (Kulhawy, 1983) 4)f from CPT (~)~ from SF1’ Rock (Canadian Geotech. Society, 1985)

0.70

SPT-method CP’I’-method Load test Pile driving analyzer

0.45 0.55 0.80 0.70

Skin friction and end bearing

Block failure

0.45 0.35 0.50

Clay

0.65

Uplift capacity of single piles

a-method 13-method X-method SPT-method CP’I’-method Load Test

0.60 0.40 0.45 0.35 0.45 0.80

Group uplift capacity

Sand Clay

0.55 0.55

ysis of soil and groundwater samples should be considered. 4.11.1.9 Nearby Structures In cases where foundations are placed adjacent to existing structures, the influence of the existing structures on the behavior of the foundation, and the effect of the foundation on the existing structures, shall be investigated. 4.11.2 B B’

c C~, Cm2

Em

Notations

footing width (in length units) reduced effective footing width (see Article 4.11.4.1.5) (in length units) = soil cohesion (in units of force/length2) = correction factors for groundwater effect (dimensionless) = depth to footing base (in length units) = depth to groundwater table (in length units) = elastic modulus of rock masses (in units of force/length2) = =

type of load reduced effective length (see Article 4.11.4.1.5) (in length units) = load type N = average value of standard penetration test blow count (dimensionless) Nm, N~m, Nqm = modified bearing capacity factors used in analytic theory (dimensionless) = cone resistance (in units of force/length2) = ultimate bearing capacity (in units of force/length2) R = reduction factor due to the effect of load inclination (dimensionless) = nominal resistance RQD = rock quality designation 5 = span length (in length units) = undrained shear strength of soil (in units 5,, of force/length2) = load factor coefficient for load type i (see 13’ Article C 4.10.4) = load factor (see Article C 4.10.4) -y = total (moist) unit weight of soil (see Artiy cle C 4.11.4.1.1) = =

96

HIGHWAY BRIDGES

TABLE 4.10.6-3

4.11.2

Performance Factors for Geotechnical Strength Limit States in Axially Loaded Drilled Shafts Performance Factor

Method/SoillCondition Ultimate bearing capacity of single drilled shafts

Side resistance in clay

a-method (Reese & O’Neill)

0.65

Base resistance in clay

Total Stress (Reese & O’Neill)

0.55

Side resistance in sand

1) 2) 3) 4) 5)

Touma & Reese Meyerhof Quiros & Reese Reese & Wright Reese & O’Neill

See discussion in article 4.13.3.3.3

Base resistance in sand

1) 2) 3) 4) 5)

Touma & Reese Meyerhof Quiros & Reese Reese & Wright Reese & O’Neill

See discussion in article 4.13.3.3.3

Side resistance in rock

Carter & Kulhawy Horvath and Kenney

0.55 0.65

Base resistance in rock

Canadian Geotechnical Society Pressuremeter Method (Canadian Geotech nical Society)

0.50

Load test

0.80

Clay

0.65

a-method (Reese & O’Neill) Belled Shafts (Reese & O’Neill)

0.55

Side resistance and end bearing Block failure Uplift capacity of single drilled shafts

Group uplift capacity

Clay

0.50

0.50

Sand

1) Touma & Reese 2) Meyerhof 3) Quiros & Reese 4) Reese & Wright 5) Reese & O’Neill

See discussion in section 4. 13.3.3.3

Rock

Carter & Kulhawy Horvath & Kenney

0.45 0.55

Load test

0.80

Sand Clay

0.55 0.55

4.11.2

DIVISION I—DESIGN

5

= differential settlement between adjacent

4) 4)’

footings = performance factor = friction angle of soil

4.11.3

Movement Under Serviceability Limit States

97

4.11.3.4

Settlement Analyses

Foundation settlements shall be estimated using deformation analyses based on the results of laboratory or in situ testing. The soil parameters used in the analyses shall be chosen to reflect the loading history of the ground, the construction sequence and the effect of soil layering.

4.11.3.1

General

Movement of foundations in both vertical settlement and lateral displacement directions shall be investigated at service limit states. Lateral displacement of a structure shall be evaluated when: —horizontal or inclined loads are present, —the foundation is placed on an embankment slope, —possibility of loss of foundation support through erosion or scour exists, or

—bearing strata are significantly inclined. 4.11.3.2

Loads

Immediate settlement shall be determined using the service load combinations given in Table 3.22.IA. Timedependent settlement shall be determined using only the permanent loads. Settlement and horizontal movements caused by embankment loadings behind bridge abutments should be investigated. In seismically active areas, consideration shall be given to the potential settlement of footings on sand resulting from ground motions induced by earthquake loadings. For guidance in design, refer to Division I-A, Seismic Design, of these Specifications. 4.11.3.3 Movement Criteria Vertical and horizontal movement criteria for footings shall be developed consistent with the function and type of structure, anticipated service life, and consequences of unacceptable movements on structure performance. The tolerable movement criteria shall be established by empirical procedures or structural analyses. The maximum angular distortion (B/s) between adjacent foundations shall be limited to 0.008 for simpIe span bridges and 0.004 for continuous span bridges. These ~/s limits shall not be applicable to rigid frame structures. Rigid frames shall be designed for anticipated differential settlements based on the results of special analyses.

Both total and differential settlements, including time effects, shall be considered. 4.11.3.4.1

Settlement of Footings on Cohesion less Soils

Estimates of settlement of cohesionless soils shall make allowance for the fact that settlements in these soils can be highly erratic. No method should be considered capable of predicting settlements of footings on sand with precision.

Settlements of footings on cohesionless soils may be estimated using empirical procedures or elastic theory. 4.11.3.4.2

Settlement of Footings on Cohesive Soils

For foundations on cohesivesoils, both immediate and consolidation settlements shall be investigated. If the footing width is small relative to the thickness of a compressible soil, the effect of three-dimensional loading shall be considered. In highly plastic and organic clay, secondary settlements are significant and shall be included in the analysis. 4.11.3.4.3

Settlements ofFootings on Rock

The magnitude of consolidation and secondary settlements in rock masses containing soft seams shall be estimated by applying procedures discussed in Article 4.11.3.4.2. 4.11.4

Safety Against Soil Failure

4.11.4.1

Bearing Capacity of Foundation Soils

Several methods may be used to calculate ultimate bearing capacity of foundation soils. The calculated value of ultimate bearing capacity shall be multiplied by an appropriate performance factor, as given in Article 4.10.6, to determine the factored bearing capacity. Footings are considered to be adequate against soil failure if the factored bearing capacity exceeds the effect

of design loads.

98

HIGHWAY

4.11.4.1.1

Theoretical Estimation

The bearing capacity should be estimated using accepted soil mechanics theories based on measured soil parameters. The soil parameter used in the analysis shall be representative of the soil shear strength under the considered loading and subsurface conditions. 4.11.4.1.2

Semi-empirical Procedures

The bearing capacity of foundation soils may be estimated from the results of in situ tests or by observing foundations on similar soils. The use of a particular in situ test and the interpretation of the results shall take local experience into consideration. The following in situ tests may be used: —Standard penetration test (SPT), —Cone penetration test (CPT), and —Pressuremeter test. 4.11.4.1.3

Plate Loading Test

Bearing capacity may be determined by load tests providing that adequate subsurface explorations have been made to determine the soil profile below the foundation. The bearing capacity determined from a load test may be extrapolated to adjacent footings where the subsurface profile is similar. Plate load test shall be performed in accordance with

the procedures specified in ASTM Standard D 1194-87 or Standard T 235-74. AASHTO

4.11.4.1.4

Presumptive Values

Presumptive values for allowable bearing pressures on soil and rock, given in Table 4.11.4.1.4-I, shall be used only for guidance, preliminary design or design of temporary structures. The use of presumptive values shall be based on the results of subsurface exploration to identify soil and rock conditions. All values used for design shall be confirmed by field and/or laboratory testing. The values given in Table 4.11 .4.1.4-1 are applicable directly for working stress procedures. When these values are used for preliminary design, all load factors shall be taken as unity.

sure that: (1) the product of the bearing capacity and an appropriate performance factor exceeds the effect of vertical design loads, and (2) eccentricity of loading, evaluated based on factored loads, is less than 1/4 of the footing dimension in any direction for footings on soils. For structural design of an eccentrically loaded foundation, a triangular or trapezoidal contact pressure distribution based on factored loads shall be used. 4.11.4.1.6

Effect of Laad Eccentricity

For loads eccentric to the centroid of the footing, a reduced effective footing area (B’ X L’) shall be used in design. The reduced effective area is always concentrically loaded, so that the design bearing pressure on the reduced effective area is always uniform. Footings under eccentric loads shall be designed to en-

Effect of Gmundwater Table

Ultimate bearing capacity shall be determined based on the highest anticipated position of groundwater level at the footing location. In cases where the groundwater table is at a depth less than 1.5 times the footing width below the bottom of the footing, reduction of bearing capacity, as a result of submergence effects, shall be considered. 4.11.4.2 Bearing Capacity of Foundations on Rock The bearing capacity of footings on rock shall consider

the presence, orientation and condition of discontinuities, weathering profiles and other similar profiles as they apply at a particular site, and the degree to which they shall be incorporated in the design.

For footings on competent rock, reliance on simple and direct analyses based on uniaxial compressive rock strengths and RQD may be applicable. Competent rock shall be defined as a rock mass with discontinuities that are tight or open not wider than one-eighth inch. For footings on less competent rock, more detailed investigations and analyses shall be performed to account for the effects of weathering, and the presence and condition of discontinuities. Footings on rocks are considered to be adequate against bearing capacity failure if the product of the ultimate bearing capacity determined using procedures described in Articles 4.11.4.2.1 through 4.11.4.2.3 and an appropriate performance factor exceeds the effect of design loads. 4.11.4.2.1

4.11.4.1.5

4.11.4.1.1

BRIDGES

Semi-empirical Procedures

Bearing capacity of foundations on rock may be determined using empirical correlation with RQD, or other systems for evaluating rock mass quality, such as the Geomechanic Rock Mass Rating (RMR) system, or Norwegian Geotechnical Institute (NGI) Rock Mass Classification System. The use of these semi-empirical procedures shall take local experience into consideration.

4.11.4.2.1

DIVISION

I—DESIGN

99

TABLE 4.11.4.1.4-1 Presumptive Allowable Bearing Pressures for Spread Footing Foundations (Modified after U.S. Department of the Navy, 1982)

Allowable Bearing Pressure (tsf) Type of Bearing Material Massive crystalline igneous and metamorphic rock: graphite, diorite, basalt, gneiss, thoroughly cemented conglomerate (sound condition allows minor cracks) Foliated metamorphic rock: slate, schist (sound condition allows minor cracks) Sedimentary rock: hard cemented shales, siltstone, sandstone, limestone without cavities Weathered or broken bedrock of any kind except highly argillacous rock (shale) Compaction shale or other highly argillacous rock in sound condition Well-graded mixture of fine- and coarse-grained soil: glacial till, hardpan, boulder clay (GW-GC, GC, SC) Gravel, gravel-sand mixtures, boulder-gravel mixtures (GW, GP, SW, SP) Coarse to medium sand, sand with little gravel (SW, SP) Fine to medium sand, silty or clayey medium to coarse sand (SW, SM, SC) Find sand, silty or clayey medium to fine sand (SP, SM, SC)

Ordinary Range

Recommended Value for Use

Very hard, sound rock

60to100

80

Hard sound rock

30 to 40

35

Hard sound rock

15 to 25

20

Medium hard rock

8 to 12

10

Medium hard rock

8 to 12

10

Very dense

8 to 12

10

Very dense Medium dense to dense Loose Very dense Medium dense to dense Loose Very dense Medium dense to dense Loose Very dense

6 4 2 4 2 1

7 5

Consistency in Place

Medium dense to dense

Loose Homogeneous inorganic clay, sandy or silty clay (CL, CH) Inorganic silt, sandy or clayey silt, varved silt-clay-fine sand

(ML, MH)

Very stiff to hard

Medium stiff to stiff Soft Very stiff to hard Medium stiff to stiff Soft

to 10 to 7 to 6 to 6 to 4 to 3 3 to 5 2 to 4 1 to 2 3 to 5 2 to 4 1 to 2 3 to 6 1 to 3 0.5 to 1 2 to 4 1 to 3 to 1 0.5

3 4 3 1.5 3

2.5 1.5

3

2.5 1.5

4

2 0.5

3 1.5 0.5

100 4.11.4.2.2 Analytic Method

The ultimate bearing capacity of foundations on rock shall be determined using established rock mechanics principles based on the rock mass strength parameters. The influence of discontinuities on the failure mode shall also be considered. 4.11.4.2.3

Presumptive Bearing Values

For simple structures on t=oodquality rock masses, values of presumptive bearing pressure given in Table 4.11.4.2.4-I may be used for preliminary design. The use of presumptive values shall be based on the results of subsurface exploration to identify rock conditions. All values used in design shall be confirmed by field and/or laboratory testing. The values given in Table 4.11.4.2.4-I are direetly applicable to working stress procedure, i.e., all the load factors shall be taken as unity. 4.11.4.2.5

Effect of Load Eccentricity

If the eccentricity of loading on a footing is less than Y6 of the footing width, a trapezoidal bearing pressure shall be used in evaluating the bearing capacity. If the eccentricity is between Y. and /4 of the footing width, a triangular bearing pressure shall be used. The maximum bearing pressure shall not exceed the product of the ultimate bearing capacity multiplied by a suitable performance factor. The eccentricity of loading evaluated using factored loads shall not exceed 3/8 (37.5%) of the footing dimensions in any direction. 4.11.4.3

4.11.5

Structural Capacity

The structural design of footings shall comply to the provisions given in Article 4.4.11 and Article 8.16. 4.11.6

Construction Considerations for Shallow Foundations

Load Test

Where appropriate, load tests may be performed to determine the bearing capacity of foundations on rock. 4.11.4.2.4

4.11.4.2.2

HIGHWAY BRIDGES

Failure by Sliding

Failure by sliding shall be investigated for footings that support inclined loads and/or are founded on slopes. For foundations on clay soils, possible presence of a shrinkage gap between the soil and the foundation shall be considered. If passive resistance is included as part of the shear resistance required for resisting sliding, consideration shall also be given to possible future removal of the soil in front of the foundation. 4.11.4.4 Loss of Overall Stability The overall stability of footings, slopes and foundation soil or rock, shall be evaluated for footings located on or near a slope using applicable factored load combinations in Article 3.22 and a performance factor of 0.75.

4.11.6.1

General

The ground conditions should be monitored closely during construction to determine whether or not the ground conditions are as foreseen and to enable pi’ompt intervention, if necessary. The control investigation should be performed and interpreted by experienced and qualified engineers. Records of the control investigations should be kept as part of the final project data, among other things, to permit a later assessment of the foundation in connection with rehabilitation, change of neighboring structures. etc. 4.11.6.2

Excavation Monitoring

Prior to concreting footings or placing backfill, an excavation shall be free of debris and excessive water. Monitoring by an experienced and trained person should always include a thorough examination of the sides and bottom of the excavation, with the possible addition of pits or borings to evaluate the geological conditions. The assumptions made during the design of the foundations regarding strength, density, and groundwater conditions should be verified during construction, by visual inspection. 4.11.6.3

Compaction Monitoring

Compaction shall be carried out in a manner so that the fill material within the section under inspection is as close as practicable to uniform. The layering and compaction of the fill material should be systematic everywhere, with the same thickness of layer and number of passes with the compaction equipment used as for the inspected fill. The control measurements should be undertaken in the form of random samples. 4.12 DRIVEN PILES 4.12.1

General

The provisions of the specifications in Articles 4.5.1 through 4.5.21 with the exception of Article 4.5.6, shall apply to strength design (load factor design) of driven piles. Article 4.5.6 covers the allowable stress design of

4.12.1

DIVISION I—DESIGN TABLE 4.11.4.2.4-1

101

Presumptive Bearing Pressures (tsf) for Foundations on Rock (After Putnam, 1981)

Sound Foliated Rock

Sound Sedimentary Rock

Soft Rock3

Soft Shale

Broken

...

10

...

(4)

25 10

10 10

4 ...

.2q~ 9,600 .2q~

.2q~ 12 .2q~

.2q~ 12 .2q~

.2q~

.2q~

.2q~

.2q~

.2q~

Yeart

Bedrock2

Baltimore

1962

100

35

BOCA Boston

1970 1970

100 100

40 50

1970 1951/1969

100 ...

100 ...

... 25

1968 1956 1967

.2q~5 100 .2q~

.2q~ 100 .2q~

Kansas City

1961/1969

.2q~

.2q~

LosAngeles

1970

10

4

3

1

NewYorkCity

1970

60

60

60

8

New York State Ohio Philadelphia Pittsburgh Richmond St. Louis San Francisco

... 1970 1969 1959/1969 1968 1960/1970 1969

100 100 50 25 100 100 3—5

40 40 15 25 40 40 3—5

15 15 10—15 25 25 25 3—5

10 8 8 10 10

8 4 1.5

1.5 1.5

Uniform Building

1970

.2q~

.2q~

.2q~

.2q~

.2q~

.2q~

Code NBC Canada New South Wales, Australia

1970 1974

... ...

... ...

100 33

13

4.5

Code

Chicago Cleveland

Dallas Detroit Indiana

1

Shale

1.5

(4)

.2q~

1

4

Note: 1—Year of code or original year and date of revision.

2—Massive crystalline bedrock. 3—Soft and broken rock, not including shale. 4—Allowable bearing pressure to be determined by appropriate city official. = unconfined compressive strength. = soil modulus = sleeve friction measured from a CPT at point con-

piles and shall be replaced by the articles in this section for load factor design of driven piles, unless otherwise stated. 4.12.2 a,

D Dh

E~

= distance between pile tip and a weaker underly-

H,

= depth of embedment of pile socketed into rock = influence factor for the effective group embed-

ing soil layer

Notations

pile perimeter area of pile tip surface area of shaft of pile cone penetration test dimensionless depth factor for estimating tip capacity of piles in rock = pile width or diameter = effective depth of pile group = depth of embedment of pile into a bearing stratum = diameter of socket = eccentricity of load in the x-direction = eccentricity of load in the y-direction =Young’s modulus of a pile

= = A, = CPT = d =

sidered H

I

K K,

nh

N N

ment moment of inertia of a pile coefficient of lateral earth pressure correction factor for sleeve friction in clay correction factor for sleeve friction in sand dimensionless bearing capacity coefficient depth to point considered when measuring sleeve friction = rate of increase of soil modulus with depth = Standard Penetration Test (SPT) blow count = average uncorrected SPT blow count along pile shaft

= = = = = =

102

HIGHWAY BRIDGES

Npi~e = OCR = PD

=

Pg

=

=

q

= = =

q1

=

P1

average SPT-N value corrected for effect of overburden number of piles in a pile group overconsolidation ratio unfactored dead load factored total axial load acting on a pile group factored axial load acting on a pile in a pile group; the pile has coordinates (X,Y) with respect to the centroidal origin in the pile group plasticity index net foundation pressure static cone resistance

limiting tip resistance q0 = limiting tip resistance in lower stratum = ultimate unit tip resistance = ultimate unit side resistance = average uniaxial compressive strength of rock cores = ultimate bearing capacity = ultimate load carried by tip of pile = ultimate load carried by shaft of pile Qug = ultimate uplift resistance of a pile group or a group of drilled shafts = ultimate bearing capacity R = characteristic length of soil-pile system in cohesive soils = spacing of discontinuities S = average spacing of piles 5,, = undrained shear strength SPT = Standard Penetration Test S. = average undrained shear strength along pile shaft td = width of discontinuities T = characteristic length of soil-pile system in cohesionless soils Wg = weight of block of soil, piles and pile cap x = distance of the centroid of the pile from the centroid of the pile cap in the x-direction X = width of smallest dimension of pile group y = distance of the centroid of the pile from the centroid of the pile cap in the y-direction Y = length of pile group or group of drilled shafts Z = total embedded pile length a adhesion factor applied to 5,, 13 = coefficient relating the vertical effective stress and the unit skin friction of a pile or drilled shaft = effective unit weight of soil 5 = angle of shearing resistance between soil and pile X = empirical coefficient relating the passive lateral earth pressure and the unit skin friction of a pile = pile group efficiency factor p = settlement = tolerable settlement = horizontal effective stress

a’,, Uav

0qp

0,, Our

4.12.2

vertical effective stress average shear stress along side of pile = performance factor = performance factor for the bearing capacity of a pile group failing as a unit consisting of the piles and the block of soil contained within the piles = performance factor for the total ultimate bearing capacity of a pile = performance factor for the ultimate shaft capacity a pile = of performance factor for the ultimate tip capacity of a pile = Performance factor for the uplift capacity of a single pile = performance factor for the uplift capacity of pile groups =

=

4.12.3

Selection of Design Pile Capacity

Piles shall be designed to have adequate bearing and structural capacity, under tolerable settlements and tolerable lateral displacements. The supporting capacity of piles shall be determined by static analysis methods based on soil-structure interaction. Capacity may be verified with pile load test results, use of wave equation analysis, use of the dynamic pile analyzer or, less preferably, use of dynamic formulas. 4.12.3.1 Factors Affecting Axial Capacity See Article 4.5.6.1.1. The following sub-articles shall supplement Article 4.5.6.1.1. 4.12.3.1.1

Pile Penetration

Piling used to penetrate a soft or loose upper stratum overlying a hard or firm stratum, shall penetrate the hard or firm stratum by a sufficient distance to limit lateral and vertical movement of the piles, as well as to attain sufficient vertical bearing capacity. 4.12.3.1.2

Groundwater Table and Buoyancy

Ultimate bearing capacity shall be determined using the groundwater level consistent with that used to calculate load effects. For drained loading, the effect of hydrostatic pressure shall be considered in the design. 4.12.3.1.3

Effect Of Settling Ground and Downdrag Forces

Possible development of downdrag loads on piles shall be considered where sites are underlain by compressible clays, silts or peats, especially where fill has recently been

4.12.3.1.3

DIVISION

placed on the earlier surface, or where the groundwater is substantially lowered. Downdrag loads shall be considered as a load when the bearing capacity and settlement of pile foundations are investigated. Downdrag loads shall not be combined with transient loads. The downdrag loads may be calculated, as specified in Article 4.12.3.3.2 with the direction of the skin friction forces reversed. The factored downdrag loads shall be added to the factored vertical dead load applied to the deep foundation in the assessment of bearing capacity. The effect of reduced overburden pressure caused by the

downdrag shall be considered in calculating the bearing capacity of the foundation. The downdrag loads shall be added to the vertical dead load applied to the deep foundation in the assessment of settlement at service limit states. 4.12.3.1.4

Uphft

103

I—DESIGN

veloped considering the potential effects of combined vertical and horizontal movement. Where combined horizontal and vertical displacements are possible, horizontal movement shall be limited to 1.0 in. or less. Where vertical displacements are small, horizontal displacements shall be limited to 2.0 in. or less (Moulton et al., 1985). If estimated or actual movements exceed these levels, special analysis and/or measures shall be considered. 4.12.3.2.3

Settlement

The settlement of a pile foundation shall not exceed the

tolerable settlement, as selected according to Article 4.12.3.2.2. 4.12.3.2.3a

Cohesive Soil

Procedures used for shallow foundations shall be used to estimate the settlement of a pile group, using the equivalent footing location shown in Figure 4.12.3.2.1-1.

Pile foundations designed to resist uplift forces should be checked both for resistance to pullout and for structural

capacity to carry tensile stresses. Uplift forces can be caused by lateral loads, buoyancy effects, and expansive soils. 4.12.3.2 Movement Under Serviceability Limit State 4.12.3.2.1

General

For purposes of calculating the settlements of pile groups, loads shall be assumed to act on an equivalent footing located at two-thirds of the depth of embedment of the piles into the layer which provide support as shown in Figure 4.12.3.2.1-1. Service loads for evaluating foundation settlement shall include both the unfactored dead and live loads for piles in cohesionless soils and only the unfactored dead load for piles in cohesive soils. Service loads for evaluating lateral displacement of foundations shall include all lateral loads in each of the load combinations as given in Article 3.22. 4.12.3.2.2

Tolerable Movement

Tolerable axial and lateral movements for driven pile foundations shall be developed consistent with the function and type of structure, fixity of bearings, anticipated service life and consequences of unacceptable displacements on performance of the structure. Tolerable settlement criteria for foundations shall be developed considering the maximum angular distortion according to Article 4.11.3.3. Tolerable horizontal displacement criteria shall be de-

4. 12.3.2.3b

Cohesionless Soil

The settlement of pile groups in cohesionless soils can be estimated using results of in situ tests, and the equiva-

lent footing location shown in Figure 4.12.3.2.1-1. 4.12.3.2.4

Lateral Displacement

The lateral displacement of a pile foundation shall not exceed the tolerable lateral displacement, as selected according to Article 4.12.3.2.2. The lateral displacement of pile groups shall be esti-

mated using procedures that consider soil-structure interaction. 4.12.3.3

Resistance at Strength Limit States

The strength limit states that shall be considered indude: —bearing capacity of piles, —uplift capacity of piles, —punching of piles in strong soil into a weaker layer, and —structural capacity of the piles. 4.12.3.3.1

Axial Loading of Piles

Preference shall be given to a design process based upon static analyses in combination with either field monitoring during driving or load tests. Load test results may be extrapolated to adjacent substructures with similar subsurface conditions. The ultimate bearing capacity of piles may be estimated using analytic methods or in situ test methods.

104 4.12.3.3.2

Analytic Estimates of Pile Capacity

Analytic methods may be used to estimate the ultimate bearing capacity of piles in cohesive and cohesionless soils. Both total and effective stress methods may be used provided the appropriate soil strength parameters are evaluated. The performance factors for skin friction and tip resistance, estimated using three analytic methods, shall be as provided in Table 4.10.6-2. If another analytic method is used, application of performance factors presented in Table 4.10.6-2 may not be appropriate. 4.12.3.3.3

Pile of Capacity Estimates Based on in Situ Tests

In situ test methods may be used to estimate the ultimate axial capacity of piles. The performance factors for the ultimate skin friction and ultimate tip resistance, estimated using in situ methods, shall be as provided in Table 4.10.6-2.

4.12.3.3.4

Piles Bearing on Rock

For piles driven to weak rock such as shales and mudstones or poor quality weathered rock, the ultimate tip capacity shall be estimated using semi-empirical methods. The performance factor for the ultimate tip resistance of piles bearing on rock shall be as provided in Table 4.10.6-2.

4.12.3.3.5

Pile Load Test

The load test method specified in ASTM D 1143-81 may be used to verify the pile capacity. Tensile load testing of piles shall be done in accordance with ASTM D 3689-83 Lateral load testing of piles shall be done in accordance with ASIM D 3966-81 The performance factor for the axial compressive capacity. axial uplift capacity and lateral capacity obtained from pile load tests shall be as provided in Table 4.10.6-2. .

4.12.3.3.6

Presumptive End Bearing Capacities

Presumptive values for allowable bearing pressures given in Table 4. 11.4. 1.4-1 on soil and rock shall be used only for guidance, preliminary design or design of temporary structures. The use of presumptive values shall be based on the results of subsurface exploration to identify soil and rock conditions. All values used for design shall be confirmed by field and/or laboratory testing. 4.12.3.3.7

4.12.3.3.2

HIGHWAY BRIDGES

When piles are subjected to uplift, they should be investigated for both resistance to pullout and structural ability to resist tension. 4.12.3.3.7a

Single Pile Uplift Capacity

The ultimate uplift capacity of a single pile shall be estimated in a manner similar to that for estimating the skin friction resistance of piles in compression in Article 4.12.3.3.2 for piles in cohesive soils and 4.12.3.3.3 for piles in cohesionless soils. Performance factors for the uplift capacity of single piles shall be as provided in Table 4.10.6-2. 4.12.3.3.7b

Pile Group Uplift Capacity

The ultimate uplift capacity of a pile group shall be estimated as the lesser of the sum of the individual pile uplift capacities, or the uplift capacity of the pile group considered as a block. The block mechanism for cohesionless soil shall be taken as provided in Figure C4. 12.3.7.2-1 and for cohesive soils as given in Figure C4. 12.3.7.2-2. Buoyant unit weights shall be used for soil below the groundwater level. The performance factor for the group uplift capacity calculated as the sum of the individual pile capacities shall be the same as those for the uplift capacity of single piles as given in Table 4.10.6-2. The performance factor for the uplift capacity of the pile group considered as a block shall be as provided in Table 4.10.6-2 for pile groups in clay and in sand. 4.12.3.3.8

Lateral Load

For piles subjected to lateral loads, the pile heads shall be fixed into the pile cap. Any disturbed soil or voids created from the driving of the piles shall be replaced with compacted granular material. The effects of soil-structure or rock-structure interaction between the piles and ground, including the number and spacing of the piles in the group. shall be accounted for in the design of laterally loaded piles. 4.12.3.3.9

Batter Pile

The bearing capacity of a pile group containing batter piles may be estimated by treating the batter piles as vertical piles. 4.12.3.3.10

Group Capacity

4.12.3.3. lOa

Cohesive Soil

Upliift

Uplift shall be considered when the force effects calculated based on the appropriate strength limit state load combinations are tensile.

If the cap is not in firm contact with the ground, and if the soil at the surface is soft, the individual capacity of

4. 12.3.3. bA

DIVISION

each pile shall be multiplied by an efficiency factor ‘q, where ‘q = 0.7 for a center-to-center spacing of three diameters and ‘q = 1 .0 for a center-to-center spacing of six diameters. For intermediate spacings, the value of ‘q may be determined by linear interpolation. If the cap is not in firm contact with the ground and if the soil is stiff, then no reduction in efficiency shall be required. If the cap is in firm contact with the ground, then no reduction in efficiency shall be required. The group capacity shall be the lesser of: —the sum of the modified individual capacities of each pile in the group, or —the capacity of an equivalent pier consisting of the piles and a block of soil within the area bounded by the piles. For the equivalent pier, the full shear strength of soil shall be used to determine the skin friction resistance, the total base area of the equivalent pier shall be used to determine the end bearing resistance, and the additional capacity of the cap shall be ignored. The performance factor for the capacity of an equivalent pier or block failure shall be as provided in Table 4.10.6-2. The performance factors for the group capacity calculated using the sum of the individual pile capacities, are the same as those for the single pile capacity as given in Table 4.10.6-2. 4.12.3.3.1%

Cohesionless Soil

The ultimate bearing capacity of pile groups in cohesionless soil shall be the sum of the capacities of all the piles in the group. The efficiency factor, ‘q, shall be 1.0 where the pile cap is, or is not, in contact with the ground. ‘rhe performance factor is the same as those for single pile capacities as given in Table 4.10.6-2. 4. 12.3.3. lOc Pile Group in .S’trong Soil Overlying a Weak or Compressible Soil

If a pile group is embedded in a strong soil deposit overlying a weaker deposit, consideration shall be given to the potential for a punching failure of the pile tips into the weaker soil stratum. If the underlying soil stratum consists of a weaker compressible soil, consideration shall be given to the potential for large settlements in that weaker layer. 4.12.3.3.11

Dynamic/Seismic Design

Refer to Division I-A, Seismic Design, of these specifications and Lam and Martin (1986a, 1986b) for guid-

105

I—DESIGN

ance regarding the design of driven piles subjected to dynamic and seismic loads. 4.12.4

Structural Design

The sti’uctural design of driven piles shall be in accordance with the provisions of Articles 4.5.7, which was developed for allowable stress design procedures. To use load factor design procedures for the structural design of driven piles, the load factor design procedures for reinforced concrete, prestressed concrete and steel in Sections 8,9, and 10, respectively, shall be used in place of the allowable stress design procedures. 4.12.4.1

Buckling of Piles

Stability of piles shall be considered when the piles extend through water or air for a portion of their lengths. 4.12.5

Construction Considerations

Foundation design shall not be uncoupled from construction considerations. Factors such as pile driving, pile splicing, and pile inspection shall be done in accordance with the provisions of this specification and Division II. 4.13 4.13.1

DRILLED SHAFTS General

The provisions of the specifications in Articles 4.6.1 through 4.6.7 with the exception of Article 4.6.5. shall apply to the strength design (load factor design) of drilled shafts. Article 4.6.5 covers the allowable stress design of drilled shafts, and shall be replaced by the articles in this section for load factor design of drilled shafts, unless otherwise stated. The provisions of Article 4.13 shall apply to the design of drilled shafts, but not drilled piles installed with continuous flight augers that are concreted as the aueer is being extracted. 4.13.2

Notations

a

= = = =

A, A, A A,,

b CPT

d

parameter used for calculating Fr area of base of drilled shaft surface area of a drilled pier cross-sectional area of socket = annular space between bell and shaft = perimeter used for calculating Fr = cone penetration test = dimensionless depth factor for estimating tip capacity of drilled shafts in rock

106 D Db

Fr

H,

HIGHWAY

diameter of drilled shaft embedment of drilled shaft in layer that provides support = diameter of base of a drilled shaft = diameter of a drilled shaft socket in rock = Young’s modulus of concrete = intact rock modulus = Young’s modulus of a drilled shaft = modulus of the in situ rock mass = soil modulus = reduction factor for tip resistance of large diameterdrilled shaft = depth of embedment of drilled shaft socketed into rock = moment of inertia of a drilled shaft = influence coefficient (see Figure = =

Quit

R RQD SPT td

T z Z Greek cx

13

C4. 13.3.3.4-1)

I,, k

K Kb

KE

LL

N

Nc,,rr

N,,

p1 P

0

PD PL

q, bell q.

QSR

influence coefficient for settlement of drilled shafts socketed in rock = factor that reduces the tip capacity for shafts with a base diameterlarger than 20 inches so as to limit the shaft settlement to 1 inch = coefficient of lateral earth pressure or load transfer factor = dimensionless bearing capacity coefficient for drilled shafts socketed in rock using pressuremeter results = modulus modification ratio = dimensionless bearing capacity coefficient (see Figure C4.13.3.3.4-4) = liquid limit of soil = uncorrected Standard Penetration Test (SPT) blow count = bearing capacity factor = corrected SPT-N value = uplift bearing capacity factor = limit pressure determined from pressuremeter tests within 2D above and below base of shaft =

at rest horizontal stress measured at the base of drilled shaft = unfactored dead load = plastic limit of soil = ultimate unit tip resistance = reduced ultimate unit tip resistance of drilled shafts = ultimate unit side resistance = unit uplift capacity of a belIed drilled shaft = unmaxial compressive strength of rock core = ultimate bearing capacity = ultimate load carried by tip of drilled shaft = ultimate load carried by side of drilled shaft = ultimate side resistance of drilled shafts socketed in rock =

4.13.2

BRIDGES

y

TI Pba,e

Pe Ptoi

ox, ci.

(1)

4)’ or 4)q 4)qr’

total ultimate bearing capacity characteristic length of soil-drilled shaft system in cohesive soils = Rock Quality Designation = spacing of discontinuities = Standard Penetration Test = undrained shear strength = width of discontinuities = characteristic length of soil-drilled shaft system in cohesionless soils = depth below ground surface = total embedded length of drilled shaft =

adhesion factor applied to 5, coefficient relating the vertical effective stress and the unit skin friction of a drilled shaft = effective unit weight of soil = angle of shearing resistance between soil and drilled shaft = drilled shaft group efficiency factor = settlement of the base of the drilled shaft = elastic shortening of drilled shaft = tolerable settlement = vertical effective stress = total vertical stress = working load at top of socket = performance factor = angle of internal friction of soil = performance factor for the total ultimate bearing capacity of a drilled shaft = performance factor for the ultimate shaft capacity of a drilled performance factorshaft for the ultimate tip capac= =

=

ity of a drilled shaft 4.13.3

Geotechnical Design

Drilled shafts shall be designed to have adequate bearing and structural capacities under tolerable settlements and tolerable lateral movements. The supporting capacity of drilled shafts shall be estimated by static analysis methods (analytical methods based on soil-structure interaction). Capacity may be verified with load test results. The method of construction may affect the drilled shaft capacity and shall be considered as part of the design process. Drilled shafts may be constructed using the dry, casing or wet method of construction, or a combination of methods. In every case, hole excavation, concrete placement, and all other aspects shall be performed in conformance with the provisions of this specification and Division II.

4.13.3.1 4.13.3.1

DIVISION

Factors Affecting Axial Capacity

See Article 4.6.5.2 for drilled shafts in soil and Article 4.6.5.3.3 for drilled shafts in rock. The following sub-articles shall supplement Articles 4.6.5.2 and 4.6.5.3.3.

107

I—DESIGN

4.13.3.2.3a

The settlement of single drilled shafts shall be estimated considering short-term settlement, consolidation settlement (if constructed in cohesive soils), and axial compression of the drilled shaft. 4. 13.3.2.3b

4.13.3.1.1

Downdrag Loads

Downdrag loads shall be evaluated, where appropriate, as indicated in Article 4.12.3.1.3. 4.13.3.1.2

Uplift

The provisions of Article 4.12.3.1.4 shall apply as applicable. Shafts designed for and constructed in expansive soil shall extend for a sufficient depth into moisture-stable soils to provide adequate anchorage to resist uplift. Sufficient clearance shall be provided between the ground surface and underside of caps or beams connecting shafts to preclude the application of uplift loads at the shaft/cap connection due to swelling ground conditions. Uplift capacity of straight-sided drilled shafts shall rely only on side resistance in conformance with Article 4.13.3.3.2 for drilled shafts in cohesive soils, and Article 4.13.3.3.3 for drilled shafts in cohesionless soils. Ifthe shaft has an enlarged base, Q, shall be determined in conformance with Article 4.13.3.3.6. 4.13.3.2 Movement Under Serviceability Limit State

Settlement of Single Drilled Shafts

Group Settlement

The settlement of groups of drilled shafts shall be estimated using the same procedures as described for pile groups, Article 4.12.3.2.3. —Cohesive Soil, See Article 4. 12.3.2.3a —Cohesionless Soil, See Article 4.1 2.3.2.3b 4.13.3.2.4

Lateral Displacement

The provisions of Article 4.12.3.2.4 shall apply as applicable. 4J.3.3.3

Resistance at Strength Limit States

The strength limit states that must be considered inbearing capacity of drilled shafts, (2) uplift capacity of drilled shafts, and (3) punching of drilled shafts bearing in strong soil into a weaker layer below.

clude: (I)

4.13.3.3.1

Axial Loading of Drilled Shafts

The provisions of Article 4.12.3.3.1 shall apply as applicable. 4.13.3.3.2 Analytic Estimates of Drilled Shaft Capacity in Cohesive Soils

4.13.3.2.1

General

The provisions of Article 4.12.3.2.1 shall apply as applicable. In estimating settlements of drilled shafts in clay, only unfactored permanent loads shall be considered. However unfactored live loads must be added to the permanent loads when estimating settlement of shafts in granular soil. 4.13.3.2.2

4.13.3.3.3

Estimation of Drilled-Shaft Capacity in Cohesionless Soils

Tolerable Movement

The provisions of Article 4.12.3.2.2 shall apply as applicable. 4.13.3.2.3

Analytic (rational) methods may be used to estimate the ultimate bearing capacity of drilled shafts in cohesive soils. The performance factors for side resistance and tip resistance for three analytic methods shall be as provided in Table 4.10.6-3. If another analytic method is used, application of the performance factors in Table 4.10.6-3 may not be appropriate.

The ultimate bearing capacity of drilled shafts in cohesionless soils shall be estimated using applicable methods, and the factored capacity selected using judgment, and any available experience with similar conditions.

Settlement

The settlement of a drilled shaft foundation involving either single drilled shafts or groups of drilled shafts shall not exceed the tolerable settlement as selected according to Article 4.13.3.2.2

4.13.3.3.4

Axial Capacity in Rock

In determining the axial capacity of drilled shafts with rock sockets, the side resistance from overlying soil deposits shall be ignored.

108

HIGHWAY

If the

rock is degradable, consideration of special construction procedures, larger socket dimensions, or reduced socket capacities shall be considered. The performance factors for drilled shafts socketed in

4.13.3.3.4

BRIDGES

or structural failure of the drilled shaft. The design of laterally loaded drilled shafts shall account for the effects of interaction between the shaft and ground. including the

number of piers in the group.

rock shall be as provided in Table 4.10.6-3. Group Capacity

4.13.3.3.8

4.13.3.3.5

Load Test

Where necessary, a full scale load test or tests shall be conducted on a drilled shaft or shafts to confirm response to load. Load tests shall be conducted using shafts constructed in a manner and of dimensions and materials identical to those planned for the production shafts. Load tests shall be conducted following prescribed written prc)cedures which have been developed from accepted standards and modified, as appropriate, for the

conditions at the site. Standard pile load testing procedures developed by the American Society for Testing and Materials as specified in Article 4.12.3.3.5 may be modified for testing drilled shafts. The performance factor for axial compressive capacity, axial uplift capacity, and lateral capacity obtained from load tests shall be as provided in Table 4.10.6-3.

4. 13.3.3.6

Uplift Capacity

Uplift shall be considered when (il upward loads act on the drilled shafts and (ii) swelling or expansive soils act on the drilled shafts. Drilled shafts subjected to uplift

forces shall be investigated, both for resistance to pullout and for their structural strength. 4.13.3.3.6a

Uplift Capacity of a Single Drilled Shaft

The uplift capacity of a single straight-sided drilled shaft shall be estimated in a manner similar to that for estimating the ultimate side resistance for drilled shafts in compression (Articles 4.13.3.3.2, 4.13.3.3.3, and

Possible reduction in capacity from group effects shall

be considered. 4. 13.3.3.8a

The provisions of Article 4.12.3.3. lOa shall apply. The performance factor for the group capacity of an equivalent pier or block failure shall be as provided in Table 4.10.62 for both cases of the cap being in contact, and not in contact with the ground. The performance factors for the group capacity calculated using the sum of the individual drilled shaft capacities are the same as those for the single

drilled shaft capacities. 4. 13.3.3.8b

ing that

the

Cohesionless Soil

Evaluation of group capacity of shafts in cohesionless soil shall consider the spacing between adjacent shafts. Regardless of cap contact with the ground, the individual capacity of each shaft shall be reduced by a factor TI for an isolated shaft, where ‘q = 0.67 for a center-to-center (CIC) spacing of three diameters and TI = 1.0 for a center-to-center spacing of eight diameters. For intermediate spacings, the value of ‘rI may be determined by linear interpc)lation. See Article 4.13.3.3.3 for a discussion on the selection of performance factors for drilled shaft capacities in cohesionless soils. 4. 13.3.3.8c

4.13.3.3.4). The uplift capacity of a belIed shaft shall be estimated neglecting the side resistance above the bell, and assuni-

Cohesive Soil

Group in Strong Soil Overlying Weaker Comp~’essible Soil

The provisions of Article 4.12.3.3.lOc shall apply as applicable.

bell behaves as an anchor.

The performance factor for the uplift capacity of

drilled shafts shall be as provided in Table 4.10.6-3. 4. 13.3.3.6b

Group Uplift Capacity

See Article 4.12.3.3.7b. The performance factors for uplift capacity of groups of drilled shafts shall be the same as those for pile groups as given in Table 4.10.6-3. 4.13.3.3.7

Lateral Load

The design of laterally loaded drilled shafts is usually governed by lateral movement criteria (Article 4.13.3.2)

4.13.3.3.9

Dynamic/Seismic Design

Refer to Division I-A, Seismic Design for guidance regarding the design of drilled shafts subjected to dy-

namic and seismic loads. 4.13.4

Structural Design

The structural design of drilled shafts shall be in accordance

with

the

provisions

of Article

4.6.6,

which was developed for allowable stress design proce-

4.13.4

DIVISION

dures. In order to use load factor design procedures for the structural design of drilled shafts, the load factor design procedures in Section 8 for reinforced concrete shall be used in place of the allowable stress design procedures.

109

I—DESIGN

4.13.4.1

Buckling of Drilled Shafts

Stability of drilled shafts shall be considered when the shafts extend through water or air for a portion of their length.

Section 5 RETAINING WALLS Part A GENERAL REQUIREMENTS AND MATERIALS

5.1

tance. Gravity walls may be constructed of stone masonry and/or unreinforced concrete. Semi-gravity cantilever, counterfort, and buttress walls are constructed of reinforced concrete. Rigid gravity and semi-gravity retaining walls may be reinforced concrete. Rigid gravity and semigravity retaining walls may be used for bridge substructures or grade separations. Rigid gravity and semi-gravity walls are generally used for permanent wall applications.

GENERAL

Retaining walls shall be designed to withstand lateral earth and water pressures, including any live and dead load surcharge, the self weight of the wall, temperature and shrinkage effects, andearthquake loads in accordance with the general principles specified in this section. Retaining walls shall be designed for a service life based on consideration of the potential long-term effects of corrosion, seepage, stray currents and other potentially deleterious environmental factors on each of the material components comprising the wall. For most applications, permanent retaining walls should be designed for a minimum service life of 75 to 100 years. The quality of inservice performance shall be an important consideration in the design of permanent retaining walls. Permanent walls shall be designed to retain an aesthetically pleasing appearance, and be essentially maintenance free throughout their design service life. Retaining walls for temporary applications are typically designed for a service life of 36 months or less.

5.2.1.2

Nongravity cantilevered walls derive lateral resistance through embedment of vertical wall elements and support retained soil with facing elements. Vertical wall elements may consist of discrete vertical elements (e.g., piles, caissons, drilled shafts or auger cast piles) spanned by a structural facing (e.g., wood or reinforced concrete lagging,

precast or cast-in-place concrete panels, wire or fiber reinforced shotcrete, or metal elements such as sheet piles). The discrete vertical elements typically extend deeper into the ground than the facing to provide vertical and lateral support. Alternately, the vertical wall elements and facing are continuous and, therefore, also form the structural facing. Typical continuous vertical wall elements include piles, precast or cast-in-place concrete diaphragm wall panels, tangent piles, and tangent caissons. Permanent nongravity cantilevered walls may be constructed of reinforced concrete and/or metals. Temporary nongravity cantilevered walls may be constructed of reinforced concrete, metal and/or timber. Suitable metals generally include steel for components such as piles, brackets and plates, lagging and concrete reinforcement. Nongravity cantilevered walls may be used for the same applications as rigid gravity and semi-gravity walls, as well as temporary or permanent support of earth slopes, excavations, or unstable soil and rock masses. Nongravity cantilevered walls are generally limited to a maximum height of approximately 15 feet, unless they are provided with additional support by means of anchors.

5.2 WALL TYPE AND CAPACITY 5.2.1

Selection of Wall Type

Selection of wall type shall be based on an assessment of the magnitude and direction of loading, depth to suitable foundation support, potential for earthquake loading, presence of deleterious environmental factors, proximity of physical constraints, tolerable and differential settlement, facing appearance, and ease and cost of construction. 5.2.1.1

Nongravity Cantilevered Walls

Rigid Gravity and Semi-Gravity Walls

Gravity and semi-gravity walls derive their capacity through combinations of dead weight and structural resisIll

112

HIGHWAY

5.2.1.3 Anchored Walls Anchored walls are typically composed of the same elements as nongravity cantilevered walls (Article 5.2.1.2), but derive additional lateral resistance from one or more tiers of anchors. Anchors may be prestressed or deadman type elements composed of strand tendons or bars (with corrosion protection as necessary) extending from the wall face to a grouted zone or mechanical anchorage located beyond the zone of soil applying load to the wall. Bearing elements on the vertical support elements or facing of the wall transfer wall loads to the anchors. In some cases, a spread footing is used at the base of the anchored wall facing in lieu of vertical element embedment to provide vertical support. Due to their flexibility and method of support, the distribution of lateral pressure on anchored walls is influenced by the method and sequence of wall construction and anchor prestressing. Anchored walls are applicable for temporary and permanent support of stable and unstable soil and rock masses. Anchors are usually required for support of both temporary and permanent nongravity cantilevered walls higher than about 15 feet, depending on soil conditions. Anchored walls are typically constructed in cut situations, in which construction occurs from the top down to the base of the wall. Anchored walls have been successfully used to support fills; however, certain difficulties arising in fill wall applications require special consideration during design. In particular, there is a potential for anchor damage due to settlement of backfill and underlying soils or due to improperly controlled backfilling procedures. Also, there is a potential for undesirable wall deflection, if anchors are too highly stressed when the backfill is only partially complete and provides limited passive resistance. 5.2.1.4 Mechanically Stabilized Earth Walls Mechanically stabilized earth (MSE) systems, whose elements may be proprietary, employ either metallic (strip- or grid-type) or polymeric (sheet-, strip-, or gridtype) tensile reinforcements in the soil mass, and a facing element which is vertical or near vertical. MSE walls may be used where conventional gravity, cantilever, or counterforted concrete retaining walls are considered, and are particularly well suited where substantial total and differential settlements are anticipated. The allowable settlement of MSE walls is limited by the longitudinal deformability of the facing and the ultimate purpose of the structure. Limiting tolerable differential settlement for systems with panels less than 30 square feet in size and a minimum joint width of 3/4 inch are presented in Table 5.2.1 .4A.

5.2.1.3

BRIDGES

TABLE 5.2.l.4A Relationship Between Joint Width and Limiting Differential Settlement for MSE Walls Joint Width

Limiting Differential Settlement

314 inch

1/100

1/2 inch 1/4 inch

1/200 1/300

Where foundation conditions indicate large differential settlements over a short horizontal distance, a vertical fullheight slip joint shall be provided. MSE walls should not be used under the following conditions: • When utilities other than highway drainage must be constructed within the reinforced zone. • With galvanized metallic reinforcements exposed to surface or ground water contaminated by acid mine drainage or other industrial pollutants as indicated by low pH and high chlorides and sulfates. • When floodplain erosion may undermine the reinforced fill zone, or where the depth of scour cannot be reliably determined. MSE walls may be considered for use under the following special conditions: • When two intersecting walls form an enclosed angle

of 70~ or less, the affected portion of the wall shall be designed as an internally tied bin structure with at-rest earth pressure coefficients.

• Where metallic reinforcements are used in areas of anticipated stray currents within 200 feet of the structure, a corrosion expert should evaluate the potential need for corrosion control requirements. 5.2.1.5

Prefabricated Modular Walls

Prefabricated modular wall systems, whose elements may be proprietary, generally employ interlocking soilfilled reinforced concrete or steel modules or bins, which resist earth pressures by acting as gravity retaining walls. Prefabricated modular systems may be used where conventional gravity, cantilever or counterfort concrete retaining walls are considered. Prefabricated modular systems shall not be used under the following conditions: • On curves with a radius of less than 800 feet, unless

the curve can be substituted by a series of chords.

5.2.1.5

DIVISION

• When calculated longitudinal differential settlements along the face of the wall are greater than 1/200. • Steel modular systems shall not be used where the ground water or surface runoff is acid contaminated or where deicing spray is anticipated.

113

I—DESIGN

factory, special exploration, testing and analyses may be required for bridge abutments or retaining walls constructed over soft subsoils where consolidation and/or lateral flow of the soft soil could result in unacceptable longterm settlements or horizontal movements. 5.2.2.4

5.2.2

Tolerable Movements

Wall Capacity

Retaining walls shall be designed to provide adequate structural capacity with acceptable movements, adequate foundation bearing capacity with acceptable settlements, and acceptable overall stability of slopes adjacent to walls. The tolerable level of structural deformation is controlled by the type and location of wall structure and surrounding facilities. 5.2.2.1

Tolerable movement criteria for retaining walls shall be developed based on the function and type of wall, anticipated service life, and consequences of unacceptable movements. Where a wall is used to support a structure, tolerable movement criteria shall be established in accordance with Articles 4.4, 4.5, and 4.6. Where a wall supports soil on which an adjacent structure is founded, the effects of wall movements and associated backfill settlement on the adjacent structure should be evaluated.

Bearing Capacity 5.2.3

Soil, Rock, and Other Problem Conditions

The bearing capacity of wall foundation support sys-

tems may be estimated using procedures described in Articles 4.4, 4.5, or 4.6, or other generally accepted theories. Such theories are based on soil and rock parameters measured by in-situ and/or laboratory tests. 5.2.2.2

Settlement

The settlement of wall foundation support systems may be estimated using procedures described in Articles 4.4,4.5, or 4.6, or other generally accepted methods. Such methods are based on soil and rock parameters measured directly or inferred from the results of in-situ and/or laboratory test. 5.2.2.3

Overall Stability

The overall stability of slopes in the vicinity of walls shall be considered as part of the design of retaining walls. The overall stability of the retaining wall, retained slope, and foundation soil or rock shall be evaluated for all walls using limiting equilibrium methods of analysis which employ the Modified Bishop, simplified Janbu or Spenser methods of analysis. A minimum factor of safety of 1.3 shall be used for walls designed for static loads, except the factor of safety shall be 1.5 for walls that support bridge abutments, buildings or critical utilities, or for other installations with a low tolerance for failure. A minimum factor of safety of 1.1 shall be used for all walls designed for seismic loads. In all cases, the subsurface conditions and soil/rock properties of the wall site shall be adequately characterized through insitu exploration and testing and/or laboratory testing as described in Article 5.3. It must be noted that, even if overall stability is satis-

Geologic and environmental conditions can influence the performance of retaining walls and their foundations, and may require special consideration during design. To the extent possible, the presence and influence of such conditions shall be evaluated as part of the subsurface exploration program. A representative, but not exclusive, listing of problem conditions requiring special consideration is presented in Table 4.2.3A for general guidance. 5.3

SUBSURFACE EXPLORATION AND

TESTING PROGRAMS The elements of the subsurface exploration and testing programs shall be the responsibility ofthe Designer based on the specific requirements of the project and his or her experience with local geological conditions. 5.3.1

General Requirements

As a minimum, the subsurface exploration and testing programs shall define the following, where applicable: • Soil strata: —Depth, thickness, and variability —Identification and classification —Relevant engineering characteristics (i.e., natural moisture content, Atterberg limits, shear strength, compressibility, stiffness, permeability, expansion or collapse potential, and frost susceptibility) —Relevant soil chemistry, including pH, resistivity, and sulfide content • Rock strata: —Depth to rock

114

—Identification and classification —Quality (i.e., soundness, hardness, jointing and presence ofjoint filling, resistance to weathering, if exposed, and solutioning) —Compressive strength (e.g., uniaxial compression, point load index) —Expansion potential • Ground water elevation, chemical composition and pH (especially important for anchored, nongravity cantilevered, modular, and MSE walls for which corrosion potential is an important consideration) • Ground surface topography • Local conditions requiring special consideration (e.g., presence of stray electrical currents). Exploration logs shall include soil and rock strata descriptions, penetration resistance for soils (e.g., SPT or ~ and sample recovery and RQD for rock strata. The drilling equipment and method, use of drilling mud, type of SPT hammer (i.e., safety, donut, hydraulic) or cone penetrometer (i.e., mechanical or electrical), and any unusual subsurface conditions such as artesian pressures, boulders or other obstructions, or voids shall also be noted on the exploration logs. 5.3.2

Minimum Depth

5.3.5

5.4 NOTATIONS The following notations shall apply for design of retaming walls: A

A, b

B Be

c C

5.3.3

C,,

Minimum Coverage

A minimum of one soil boring shall be made for each retaining wall. For retaining walls over 100 feet in length, the spacing between borings should be no greater than 100 feet. In planning the exploration program, consideration should be given to placing borings inboard and outboard of the wall line to define conditions in the scour zone at the toe of the wall and in the zone behind the wall to estimate lateral loads and anchorage capacities.

D

Laboratory Testing

Laboratory testing shall be performed as necessary to determine engineering characteristics including unit weight, natural moisture content, Atterberg limits, shear strength, compressive strength and compressibility. In the absence of laboratory testing, engineering characteristics may be estimated based on published test results or local experience.

Scour

The probable depth of scour shall be determined by subsurface exploration and hydraulic studies. Refer to Artide 1.3.2 and FHWA (1988) for general guidance regarding hydraulic studies and design.

Refer to Article 4.3.2 regarding the selection of minimum depths of exploration for retaining walls supported on various types of foundations.

5.3.4

5.3.1

HIGHWAY BRIDGES

f F

Acceleration coefficient (dim); (See Article 3.2, Division I-A) = Surface area of transverse reinforcement in bearing (diameter times length) (Ct2); (See Article 5.8.5) = Maximum wall acceleration coefficient at the centroid (dim); (See Article 5.8.10.1) = Total surface area of reinforcement beyond failure plane (ft2); (See Article 5.8.5) = Width of bin module or width of discrete vertical wall element (ft); (See Articles 5.6.2 and 5.9.4) = Reinforcement width for layer i (ft); (See Article 5.8.10.2) = Width of retaining wall foundation (ft) = Width of excavation perpendicular to wall (ft); (See Article 5.7.5) = Cohesion of soil (kst) = Combined response coefficient at ground level (dim); (See Articles 3.21.2.1 or 3.21.2.2) = Adhesion between cohesive soil and concrete (ksf) Uniaxial compressive strength of intact rock (ksf) = Design embedment depth of vertical wall element (ft) = Embedment of continuous vertical wall element required for equilibrium of overturning and resisting moments (ft); (See Article 5.6.2) = Thickness of metal reinforcement at end of service life (mil); (See Article 5.8.6.1) = Nominal thickness of steel reinforcement at construction (mil); (See Article 5.8.6.1) = Sacrificed thickness of metal expected to be lost by uniform corrosion during service life of structure (mil); (See Article 5.8.6.1) = Coefficient of friction between wall and soil or rock (dim); (See Article 5.5.2) = Sum of forces resisting sliding (k/ft); (See Article =

5.5.5) =

Apparent coefficient of friction at each reinforcement level (dim); (See Article 5.8.5)

5.4

FC

fd

FD

FS h

H H 1 H2 H, H,,

K K,, K,,

L

e

m

m

Mm,,,

n n N

Pb

DIVISION I—DESIGN

Factor of safety for polymeric reinforcements with respect to construction damage (dim); (See Article 5.8.7.2) = Coefficient of resistance to direct sliding of reinforcement (dim); (See Article 5.8.5) = Factor of safety for polymeric reinforcements with respect to environmental and aging losses (dim); (See Article 5.8.7.2) = Factor of safety (dim) = Equivalent height of soil representing surcharge pressure or effective total height of soil at back of reinforced soil mass (ft); (See Article 5.8.2) = Design wall height (ft)

P,

cavation base acting inwardly at the mid-height of the embedded length of wall (k/ft); (See Article 5.7.5) = Pullout capacity developed by passive resistance per grid (k); (See Article 5.8.5) = Pullout capacity per strip (k); (See Article 5.8.5) = Resultant of lateral pressure due to line surcharge load (k/ft); (See Article 5.5.2) = Horizontal component of earth pressure resultant (k/ft); (See Article 5.5.2) = Pressure inside bin module (ksf); (See Article

PN

=

=

Equivalent wall height (ft); (See Article 5.8.4.1) Effective wall height (ft); (See Article 5.8.10.1) Surcharge height (ft of soil); (See Article 5.5.2) Height of water in backfill above base of wall (ft) = Earth pressure coefficient (dim); (See Article 5.5.2) = Active earth pressure coefficient (dim); (See Article 5.5.2) = At-rest earth pressure coefficient (dim); (See Article 5.5.2) = Passive earth pressure coefficient for curved failure surface (dim); (See Article 5.5.2) = Passive earth pressure coefficient for planar failure surface (dim); (See Article 5.5.2) = Length of mat beyond failure plane (ft); (See Article 5.8.5) = Length of soil reinforcing elements (ft); (See Article 5.8.2) = Center-to-center spacing of discrete vertical wall elements (ft); (See Article 5.6.2) = Effective reinforcement length for layer i (ft); (See Article 5.8.10.2) = Ratio of horizontal distance between surcharge load and wall to vertical wall height (dim); (See Article 5.5.2) = Reduction factor for active earth pressure on walls with more than one row of anchors (dim); (See Article 5.7.2) = Maximum bending moment in vertical wall element or facing (k-ft/ft) = Ratio of depth below top of wall to total vertical wall height (dim); (See Article 5.5.2) = Number of transverse bearing members behind failure plane (dim); (See Article 5.8.5) = Stability number (dim); (See Article 5.6.2) = Passive resistance factor; (See Article 5.8.5) = Design lateral pressure at any depth (ksf) = Resultant of active earth pressure (k/ft) = Net unbalanced horizontal force below base of the exposed wall resulting from an unstable ex= = = =

115

Ptg

PH PH

5.9.4)

PN P,,

PT Pv

q QL

R

RF

s5Hi

T

Tmd

Resultant of lateral pressure due to point surcharge load (k); (See Article 5.5.2) = Normal component of earth pressure resultant (k/ft); (See Article 5.5.2) = Resultant of at-rest earth pressure (k/Ct); (See Artide 5.5.2) = Resultant of passive earth pressure (k/ft); (See Article 5.5.2) = Resultant of uniform pressure distribution on wall due to uniform surcharge loading (k); (See Article 5.5.2) = Tangential component of earth pressure resultant (k/ft); (See Article 5.5.2) = Vertical component of earth pressure resultant (k/ft); (See Article 5.5.2) = Resultant of hydrostatic pressure due to water in backfill (k/ft); (See Article 5.5.3) = Surcharge pressure (ksf); (See Article 5.8.2) = Line surcharge load (k); (See Article 5.5.2) = Point surcharge load (k); (See Article 5.5.2) = Unconfined compressive strength of soil (ksf) = Resultant of foundation bearing pressure (k or k/ft) = Distance above wall base to resultant of lateral pressure due to surcharge (ft); (See Article 5.5.2) = Reduction factor applied to Coulomb passive earth pressure coefficient to account for effects of wall friction and failure surface curvature (dim); (See Article 5.5.2) = Shear strength of rock (ksf) = Horizontal reinforcement spacing for layer i (ft); (See Article 5.8.10.2) = Undrained shear strength of cohesive soil (ksf) = Period of reinforced soil structure subjected to seismic loading (see); (See Article 5.8.10.1) = Allowable long-term reinforcement tension load for limit state (k); (See Article 5.8.7.2) = Allowable long-term reinforcement tension load for serviceability state (k); (See Article 5.8.7.2) = Limit state reinforcement tension (k); (See Artidc 5.8.6.2) = Incremental dynamic inertia force at level i (k/ft of structure); (See Article 5.8.10.2)

116

HIGHWAY

= V

1

V2 w Z

13 13’ y y 5 A P

o 4) 4)’ a’,,

Serviceability state reinforcement tension (k); (See Article 5.8.7.2)

Weight of reinforced soil mass (k/Ct); (See Article 5.8.2) = Weight of sloping soil surcharge on top of reinforced soil mass (k/ft); (See Article 5.8.2) = Width of mat (ft); (See Article 5.8.5) = Depth below effective top of wall or to reinforcement (ft); (See Article 5.8.5) = Inclination of ground slope behind wall measured counterclockwise from horizontal plane (deg); (See Article 5.5.2) = Inclination of ground slope in front of wall measured counterclockwise from horizontal plane (deg); (See Article 5.6.2) = Soil unit weight (kef) = Effective unit weight of soil or rock (kcf) = Unit weight of water (kef) = Friction angle between two dissimilar materials (deg); (See Article 5.5.2) = Maximum horizontal wall deflection (ft) = Soil reinforcement angle of friction (deg); (See Article 5.8.5) = Inclination of back of wall measured clockwise from horizontal plane (deg); (See Article 5.5.2) = Friction angle of soil = Effective stress friction angle of internal friction (deg) = Active earth pressure (ksf); (See Article 5.5.2) = Magnitude of lateral pressure due to surcharge (ksf); (See Article 5.5.2) = Passive earth pressure (ksf); (See Article 5.5.2) =

The notations for dimension units include the following: deg = degree; dim = dimensionless; ft = in. foot; = kip;lbk/ft 2; kcf = kip/ft3; = kinch; = = kip/ft; = kip/ft pound; milksf = 0.001 in.; and psi = pounds per square inch. The dimensional units provided with each notation are presented for illustration only to demonstrate a dimensionally correct combination of units for the wall design procedures presented herein. If other units are used, the dimensional correctness of the equations should be confirmed.

5.4

BRIDGES

5.5.2

Earth Pressure and Surcharge Loadings

Earth pressure loading on rigid gravity and semi-gravity walls is a function of the type and condition of soil backfill, the slope of the ground surface behind the wall, the friction between the wall and soil, and the ability of the wall to translate or rotate in response to loading. Yielding walls are free to translate or rotate about their base. Restrained walls are fixed or partially restrained against translation and/or rotation. For yielding walls, lateral earth pressures shall be computed assuming active stress conditions and wedge theory using a planar surface of sliding defined by Coulomb Theory. Development of an active state of stress in the soil behind a rigid wall requires an outward rotation of the wall about its toe. The magnitude of rotation required to develop active pressure is a function of the soil type and conditions behind the wall, as defined in Table 5.5.2A. Refer to Figure 5.5.2B for procedures to determine the magnitude and location of the earth pressure resultant for gravity and semi-gravity retaining walls subjected to active earth pressures. For restrained or yielding walls for which the tilting or deflection required to develop active earth pressure is not tolerable (i.e., yielding walls located adjacent to structures sensitive to settlement),lateral earth pressures shall be computed assuming at-rest conditions using the relationships: P,, = (y’H2/2)(K,,)

K,, =

I

—

sin4)’

5.5

5.5.1

RIGID GRAVITY AND SEMI-GRAVITY WALL DESIGN Design Terminology

Refer to Figure 5.5.1 A for terminology used in the design of rigid gravity and semi-gravity retaining walls.

(5.5.2-2)

When traffic can come within a horizontal distance from the top of the wall equal to one-half the wall height, the lateral earth pressure for design shall be increased by a mmnimum surcharge acting on the backslope equivalent to that applied by 2 feet of soil as described in Article 3.20.3. The surcharge will result in the application of an additional uniform pressure on the back of the wall having a resultant magnitude: P,= (H3y’K

Part B SERVICE LOAD DESIGN METHOD ALLOWABLE STRESS DESIGN

(5.5.2-I)

(5.5.2-3)

acting at the mid-height of the wall where K is equal to K, or K,, depending on wall restraint. If the surcharge is greater than that applied by 2 feet of soil, the design earth pressures shall be increased by the actual amount of the surcharge. Unless actual data regarding the magnitude of anticipated surcharge loads is available, assume a minimum soil unit weight of 0.125 kcf in determining the surcharge load. The effects of permanent point or line surcharge loads (other than normal traffic live loads) on backslopes shall

5.5.2

117

DIVISION I—DESIGN

I BUTTRESS-...~’ I I

STRUCTU~A L KEY BETWEEN CONCRETE POURS~ I I

STRUCTURAL KE~ I I

I BASE, BASE SLAB OR FOOTING

FIGURE 5.5.lA

Terms Used in Design of Rigid Retaining Walls

TABLE 5.5.2A Relationshipbetween Soil Backfill Type and Wall Rotation to Mobilize Active and Passive Earth Pressures Behind Rigid Retaining Walls Soil Type and Condition Dense Cohesionless Loose Cohesionless Stiff Cohesive Soft Cohesive

Wall Rotation, AIH Active Passive 0.001 0.004 0.010 0.020

0.020 0.060 0.020 0.040

118

HIGHWAY BRIDGES

5.5.2

TABLE 5.5.2B Ultimate Friction Factors, Friction Angles and Adhesion for Dissimilar Materials After U.S. Department of the Navy (1982) Friction Factor, f tan ~ (DIM)

Friction(i) Angle, ~ (Degrees)

0.70 0.55 to 0.60 0.45 to 0.55

35 29 to 31 24 to 29

Interface Materials Mass concrete on the following foundation materials: —

—

—

—

—

—

—

Clean sound rock Clean gravel, gravel-sand mixtures, coarse sand Clean fine to medium sand, silty medium to coarse sand, silty or clayey gravel Clean fine sand, silty or clayey fine to medium sand Fine sandy silt, nonplastic silt Very stiff and hard residual or preconsolidated clay Medium stiff and stiff clay and silty clay (Masonry on foundation materials has same friction factors)

0.35 to 0.30 to 0.40 to 0.30 to

Steel sheet piles against the following soils: Clean gravel, gravel-sand mixtures, well-graded rock fill with spalls — Clean sand, silty sand-gravel mixture, single-size hard rock fill Silty sand, gravel or sand mixed with silt or clay Fine sandy silt, nonplastic silt

0.45 0.35 0.50 0.35

to 17 to 22 to 17 to 19

24 19 26 19

0.40

22

0.30 0.25 0.20

17 14 11

—

0.40 to 0.50

22 to 26

—

0.30 to 0.40 0.30 0.25

17 to 22 17 14

0.70 0.65 0.55 0.50 0.30

35 33 29 26 17

—

— —

Formed concrete or concrete sheet piling against the following soils: Clean gravel, gravel-sand mixture, well-graded rock fill with spalls — Clean sand, silty sand-gravel mixture, single size hard rock fill Silty sand, gravel or sand mixed with silt or clay Fine sandy silt, noaplastic silt —

Various structural materials: — Masonry on masonry, igneous and metamorphic rocks: • Dressed soft rock on dressed soft rock • Dressed hard rock on dressed soft rock • Dressed hard rock on dressed hard rock Masonry on wood (cross grain) Steel on steel at sheet pile interlocks —

—

Interface Materials Very soft cohesive soil Soft cohesive soil Medium stiff cohesive soil Stiff cohesive soil Very stiff cohesive soil = friction angle between 2 dissimilar malerials.

Soil Cohesion, c (psO

Adhesion, ca (psO

(0- 250) (250 - 500) (500 - 1,000) (1,000 - 2,000)

0250 -

250 500

500 -

750

750 -

950

(2,000 - 4,000)

950 - 1,300

5.5.2

DIVISION I—DESIGN

o

\

119

I’

H P ——

a

~‘

1< 7H a

90

2

a

sins

9

sin(9—d)

(1)~’

K

a

9

(9.44d)

]

Sin

K—

—

2

0

[i+J~

2

E~ECTIVE UNIT WEIGHT

•‘= EF~FECTIVE ANGLE OF INTERNAL RRICTION 6

—

ANGLE 0F WALL FRICTION(SEE TABLE 5.5.26]

FIGURE 5.5.2B Computational Procedures for Active Earth Pressures Coulomb Analysis also be considered in developing the design earth pressures. See Figure 5.5.2C to estimate the effects of permanent point and line surcharge loads. The effects of compacting backfill in confined areas behind retaining walls may result in development of lateral pressures greater than those represented by active or at-rest conditions. Where use of heavy static and vibratory compaction equipment within a distance of about OSH behind the wall is anticipated, the effects of backfill conipaction should be considered in estimating the lateral earth pressure distribution used for design. In addition to the earth, surcharge and water pressures, the backwalls of abutments shall be designed to resist loads due to design live and impact loads. For design purposes, it shall be assumed that wheel loads are positioned to generate the maximum tensile stresses at the back of the backwall when combined with stresses caused by the backfill. The resistance due to passive earth pressure in front of the wall shall be neglected unless the wall extends well

below the depth of frost penetration, scour or other types of disturbance (e.g., a utility trench excavation in front of wall). Where passive earth pressure in front of a wall can be considered, refer to Figures 5.5.2D and 5.5.2E for procedures to determine the magnitude and location of the passive earth pressure resultant for gravity and semigravity walls. Development of passive earth pressure in the soil in front of a rigid wall requires an outward rotation of the wall about its toe or other movement of the wall into the soil. The magnitude of movement required to mobilize passive pressure is a function of the soil type and condition in front of the wall as defined in Table 5.5.2A.

5.5.3

Water Pressure and Drainage

Walls shall be designed to resist the maximum anticipated waterpressure. For a horizontal, static ground water

120

5.5.3

HIGHWAY BRIDGES Pomni load

o~.

La’. load

Op

~emI4 ‘21Yv4

-F-,•*I

N

N

0~

L

14

PLAN

SECT1ON

SECTION

POINT LOAD

LINE LOAD

-S

C

a U

2 0

Value of

~tu6 at

.M

N2

Op

POINT LOAD

LINE LOAD

FIGURE 5.5.2C Procedure to Determine Lateral Pressure Due to Point and Line Loads Modified after Terzaghi (1954) table, the total hydrostatic water pressure shall be determined using the following relationship: 2/2

P,, =y,,H,,

(5.5.3-1)

If the ground water levels differ on opposite sides of a wall, the effects of seepage forces on wall stability or piping potential shall be considered. Seepage forces may be determined by flow net procedures or various analytical methods. Hydrostatic pressures and seepage shall be controlled by providing free dr’tining granular backfill and

weep holes through the wall. Weep pipes shall be placed through the wall at the lowest elevation that will permit gravity drainage. Portions of walls below the level of weep pipes shall be designed for full hydrostatic pressure unless a deeper drainage pipe is provided behind amid at the base of the wall. 5.5.4

for

Seismic Pressure

Refer to Section 6 of Division I-A—Seismic Desiemi guidance regarding the lateral earth pressure on gray-

5.5.4

DIVISION

REDUCTION POE VARIOUSFACTOR RATlOS (RF)OF OF4/~K~

KpIRF

121

I—DESIGN

K’1

~%&~t07I-~i.~5i-O4I.O3i..412I-t1l I ~o

IE a

I U

w

0

Ia

20

30

40

45

ANGLE OF INTERNAL FRIcTbON,~,DEGREES FIGURE 5.5.20 Computational Procedures for Passive Earth Pressures for Sloping Wall with Horizontal Backfill (Caquot and Kerisel Analysis) Nlodified alter the U.S. Department of Navy (1982)

122

HIGHWAY

N~JCT10U ~TOE (RF) OFKp POIWaGWNAT10SOF-8/~

;~ 95 —

20

~ ~ ~

45

—. 7 —. .m

-~ — s~

.861 — i ii. — i56 .S~

-.0,5 — see

907 — 562

5.5.4

BRIDGES

KpZRFEKp

1-02 s ‘~iT~ s~ ~.rn

~4l a 10.0 L

am La~ 886 I 854 6.10 ~jT7I — IT 8241117 .752 716 678 ~T~iT ii. i~ I~ £Ii~T~ .3yi~

ma mo i~ .175 .811 .7~ .~ ~ ~ ~3TJ3575 ~ .733 ~612 592 2 14.19 JIG 716 .800 .500 464 .3391276 226

1292 .114

I I&,z-g

S

.8.

20

40

45

ANGLE OF INTERNAL FRICTION, ~, DEGREES FIGURE 5.5.2E Computational Procedures for Passive Earth Pressures for Vertical Wall with Sloping Backfill (Caquot and Kerisel Analysis) Modified after the U.S. Department of Navy (1982)

.~9

5.5.4

DIVISION

ity and semi-gravity retaining walls subjected to seismic loading. In general, the pseudo-static approach developed by Mononobe and Okabe may be used to estimate the equivalent static forces for seismic loads. The estimation of seismic design forces should account for wall inertia forces in addition to the equivalent static-forces. Where a wall supports a bridge structure, the seismic design forces should also include seismic forces transferred from the bridge through bearing supports which do not slide freely (e.g., elastomeric bearings).

5.5.5

Structure Dimensions and External Stability

Gravity and semi-gravity walls shall be dimensioned to ensure stability against possible failure modes by satisfying the following factor of safety (FS) criteria: • Sliding

-

FS =

1.5

• Overturning FS =

2.0 for footings on soil

FS = 1.5

for footings on rock • Bearing Capacity for static loading See Article 4.4.7 for footings on soil See Article 4.4.8 for footings on rock • The factors of safety against sliding and overturning failure under seismic loading may be reduced to 75% of the factors of safety listed above. Bearing capacity for seismic loading FS = 1.5 for footing on soil or rock -

Refer to Figure 5.5.SA for computational procedures to determine the factors of safety for sliding and overturning failure modes using the Coulomb analysis. Unfactored dead and live loads shall be used to determine the FS against sliding and overturning. In determining the FS, the effect of passive soil pressure resistance in front of a wall should only be considered when competent soil or rock exists which will not be removed or eroded during the structure life. Table 5.5. 2A may be used for general guidance in selecting coefficients of sliding friction between the wall base and foundation soil or rock. For static loading the location of the bearing pressure resultant (R) on the base of the wall foundation shall be within B/6 of the center of the foundation for foundations on soil and within B/4 of the center of the foundation for foundations on rock where B is the width of the wall base or footing. For seismic loading, the location of R shall be within B/3 of the center of the foundation for foundations on soil and rock. See Article 4.4.5 for procedures to determine the required embedment depth of wall foundations; Articles 4.4.7 and 4.4.8, respectively, for procedures to design

123

I—DESIGN

spread footings on soil and rock; and Articles 4.5 and 4.6, respectively, for procedures to design pile and drilled shaft foundations.

5.5.6

Structure Design

Structural design of individual wall elements shall be by service load or load factor design methods in conformance with Article 3.22.

5.5.6.1

Base or Footing Slabs

The rear projection or heel of base slabs shall be designed to support the entire weight of the superimposed materials, unless a more exact method is used. The base slabs of cantilever walls shall be designed as cantilevers supported by the wall. The base slabs of counterforted and buttressed walls shall be designed as fixed or continuous beams of spans equal to the distance between counterforts or buttresses. The critical sections for bending moments in footings shall be taken at the face and back of the stem. The critical sections for shear in footings shall be taken at a distance d (d = effective depth) from the face of the stem for the toe section and at the back of the stem for the heel section.

5.5.6.2 Wall Stems The upright stems of cantilever walls shall be designed as cantilevers supported at the base. The upright stems or face walls of counterfort and buttress walls shall be designed as fixed or continuous beams. The face walls (or stems) shall be securely anchored to the supporting counterforts or buttresses by means of adequate reinforcement. Wall stems shall be designed for combined axial load (including the weight of the stemn and friction due to backfill acting on the stem) and bending due to eccentric vertical loads, surcharge loads and earth pressure.

5.5.6.3

Counterforts and Buttresses

Counterforts shall be designed as T-beamim. Buttresses shall be designed as rectangular beams. In connection with the main tension reinforcement of counterforts, there shall be a system of horizontal and vertical bars or stirrups to anchor the face walls and base slab to the counterfort. These stirrups shall be anchored as near to the outside faces of the l’ace walls, and as near to the bottom of the base slab as practicable.

124

5.5.6.3

HIGHWAY BRIDGES

I

DESIGN FACTORS w

mos of -~ ma s.d dem 1w yeeay ma emo~eeay .de~ SI .de s.d led s.•Se Seem is. s.d cew~tetWI ede~ = ~ematmt SI .com w eI—eet pE’05ua0 ode. — Vellee cs..ommt of P p — em t9o~— 4 4)

leo cm.t8

— sos. of

P P P

14m1mW oomemmt

—

P

p

F’

1

tee

-

e a

— — —

of P’~

P,, —PcoetO~—* .4) Pins. s.d ems.,.. IrUSI of Sm mew Sop Sde, .4

Iwees ~reddS4 ,emtmee SI Ses. .4 med

S,dMO~

Ms~e.4 P1.41w betees. eqiin to Owe Rs.’. miWle

—

1w

I

Is a&deoq

soUl *U~ s. mE tei

CoeflidmI .1 P4011w bates. S..,, reis — CaSed., of f.g,deIieI’ gel.

IA heOlSeAti. beUls.. Pm, T..

ma Im.4ee~k~A s.d w

—

s.s.m.

‘ode.

s.s.m

mPmgmef feomdetIs.

Slew

-

- AEI.,

SOtues. aSms.

ete slow, .,wma sag sited SSW~ frulyl Tde S.5.~

6

—

fReest. m~e .4 atwoes S1e~.m .~ s.d w rode.

F’S

—

F’eetwef sifetp

RfWMi~ m o’

4@it*s.i

San, memiw s.e.c tea RedsShoe 1wYImI5 ~

Oddsq

- I~o 5 1.5 (1w Sins. res.)

~ 2.0 (1w Sm — eel) ft30

I

UneOsbeg omees. led t ~ — F’ — c~(S —~) + .(in) + Qewsdw sod

F’ — (U F’

+

— (5.

w eeSIed teems. s.d (C — 0) P,,,)lm I + P~

~

)tas I

•

s()

• P0

Pp —

F’

F’S ——5 1.5 ‘P

Ides.

M F’w edoeds. s.d. does. heEl — meet mliod ~

ed @04 ,odseeds c

to

LOCAlION OF R(3LTANT S... mains. met em U, P V mmee0~ P~ — 0 • — — sx s S • — — A S S 4

U

— (1w Sm s. eed) S U — (1w Sm

m rode)

F’UZA~ WJ~ Te leu,iePm leedelge. reIw Is A4iIdee 45 (GeSm ~ee) @04 4 A (CoOed SledOs)

detause’s s.eedse

&‘

(SpmE F’oetkop).

0’.~A&L STAJTY ets.YSE od. SmU. ma lemets. mewds elM’ Is des. eteeg Sme es dwS~ le MUds 52.2.5

CetaUme seed reeeeel

FIGURE 5.5.5A Design Criteria for Rigid Retaining Walls Coulomb Analysis

DIVISION I—DESIGN

5.5.6.4

5.5.6.4

01

Reinforcement

Except in gravity walls, not less than 1/8 squaw inch horizontal reinforcement per foot of height shall be pro-

vided near exposed surfaces not otherwise reinforced to resist the formation of temperature and shrinkage cracks. The reinforcement in each construction panel (i.e., between vertical construction joints) of wall with height varying uniformly from one end to another, shall be designed for the loading comidhiomi acting at one-third of the panel length from the high end of the panel. If practical, the thickness of footings shall be maintained consumil in each panel or in each group of panels. The width of footings. however, mitay vary according to the height of wall as required by design. Tension reinforcement at the bottom of the heel shall be provided if required during the construction Stage prior to wall backfill. The adequacy of reinforcement shall be checked due to the dead load of the stein and any other vertical loads applied to the stem prior to backti Iling. Reinforcement in wall and abutmemu stetns shall be extended a minimum distance equal to the effective depth of the section or 15 bar diameters, whichever is greater. but not less than I t’oot beyond the point at which comnputa— tiomis indicate reinforcement is no longer needed to resist stress. 5.5.6.5

Expansion and Contraction Joints

Contraction joints shall be provided at intervals not exceeding 30 feet and expansion joints at intervals not exceeding 90 feet for gravity or reinforced concrete walls. All joints shall be filled with approved tilling material to ensure the function of the joint. Joints in abutments shall he located approximately midway between the longitudinal members bearing on the abutments. 5.5.7

Backfill

‘J’he backlill material behind all retaining walls shall be free draining. nonexpansive, noncorrosive material and shall be drained by weep holes with French drains, placed a suitable intervals and elevations. In counterfort walls, there shall be at least one drain for each pocket formed by the counterforts. Silts and clays shall not be used for backtill unless suitable design procedures are followed and construction control measured are incorporated in the construction documents to account for their presence.

5.5.8

Overall Stability

Refer to Article 5.2.2.3.

125

5.6 NONGRAVITY CANTILEVERED WALL DESIGN 5.6.1

Design Terminology

A nongravity cantilevered wall includes an exposed design height (H) over which soil is retained by the vertical and facing elements, and a vertical element embedment depth (D) which provides lateral support to the vertical wall elements. 5.6.2

Earth Pressure and Surcharge Loadings

Lateral earth pressures shall be estimnated assumine wedge theory using a planar surface of sliding (letined by Coulomb theory. For determining lateral earth pressures on permanent walls, effective stress methods of analysis and drained shear strength parameters for soil shall be used. For permanent walls and for temporary walls in granular soils, the simplified earth pressume distributions shown in Figures 5.6.2A and 5.6.2B. or other suitable earth pressure distributions, may be used. If walls will support or are supported by cohesive soils for temporary applications, walls may be designed based on total stres’~ methods of analysis amid undrained shear strength paramneters. For this latter case, the simplitied earth pressure distributions shown in Figures 5 6 ~C and 5.6.21). or other suitable earth pressure distributions. may be used with the tollowing restrictions: o The ratio of overburden pressure o undrained shear

o

strength (i.e., stability number N = -yl-lIc) must be

(4) SURCHARGE AND WATER PRESSURES MUST BE ADDED

I ~F

1.0 TSF)

TO THESE EARTH PRESSURE

0.25 H

DIAGRAMS. THE TWO LOWER DIAGRAMS ARE NOT VALID FOR PERMANENT WALLS OR WALLS WHERE WATER LEVEL LIES ABOVE BOTTOM OF EXCAVATION.

(3)

O.4y H

FIGURE 5.7.2A

5.7.4

Guidelines for Estimating Earth Pressure on Walls with Two or More Levels of Anchors Constructed from the Top Down Modified after Terzaghi and Peck (1967)

Seismic Pressure

Refer to Section 6 of Division I-A—Seismic Design for guidance regarding the design of anchored retaining walls subjected to dynamic and seismic loads. In general, the pseudo-static approach developed by Mononobe and Okabe may be used to estimate the equivalent static forces provided the maximum lateral earth pressure be computed using a seismic coefficient k5=l.SA. Forces resulting from wall inertia effects may be ignored in estimating the seismic lateral earth pressure.

5.7.5

Structure Dimensions and External Stability

The design of anchored walls includes determination of the following: o

Size, spacing, and depth of embedment of vertical wall elements and facing;

o Type, capacity, spacing, depth, inclination and cor-

rosion protection of anchors; and o Structural capacity and stability of the wall, wall

foundation, and surrounding soil mass for all intermediate and final stages of construction.

132

5.7.5

HIGHWAY BRIDGES

0.0

z 0 F

0.3 0.5

I—

z

w 0 w x w 0 U) 0~

Lii 0 2.0

0.0

2.0 DISTANCE FROM EXCAVAllON DEPTH OF EXCAVATION

CURVE I

=

Sand

CURVE It = Stiff CURVE lit = Soft

to very

hard clay

to medium

clay, factor of heave (m &.lSu ‘~ yH+q

Safety against basal Equal to 2.0

CURVE ~ = Soft to medium clay, factor of Safety against basal heave S.lSu

(

Equal to

1.2

‘~

‘~ /

‘~

yH+q/

FIGURE 5.7.2B

Settlement Profiles Behind Braced or Anchored Walls Modified after Clough and O’Rourke (1996)

The bearing capacity and settlement of vertical wall elements under the vertical component of the anchor forces and other vertical loads shall be determined in accordance with Articles 4.4, 4.5, or 4.6. For walls supported in or through soft clays with 5, O.3~y’H, continuous vertical elements extending well below the exposed base of the wall maybe required to prevent heave in front of the wall. Otherwise, the vertical elements are embedded several feet as required for stability or end bearing. (Where significant embedment of the wall

Refer to Article 5.7.2 for general guidance regarding wall deflections.

5.7.6

Structure Design

<

Depending on the characteristics of the wall, the wall components shall be designed by service load or load factor methods in conformance with Article 3.22. 5.7.6.1

General

is required to prevent bottom heave, the lowest section of

wall below the lowest row of anchors must be designed to

The procedure for anchored wall design depends on the

resist the moment induced by the pressure acting between the lowest row of anchors and the base of the exposed wall, and the force Pb O.7(yHB~ — I .4c1-l — pcB~) acting at the midheight of the embedded depth of the wall.)

number of anchor rows and the construction seqttence.

=

The required embedment depth (D or D,) may be deterinined in accordance with Article 5.6.2.

For a typical wall with two or more row’s of anchors constructed from the top down, the procedure requires design for the final structure with multiple rows of anchors and checking the design for the various stages of wall construction.

DIVISION I—DESIGN

5.7.6.1

133

The required horizontal component of each anchor force shall be computed using the apparent earth pressure

vertical wall elements and facing within allowable values. The capacity of each anchor shall be verified as part of a

distributions in Figure 5.7.2A, or other applicable earth pressure distributions, and any other horizontal water

stressing and testing program. (See Division II.)

pressure. surcharge or seismic forces acting on the wall.

The total anchor force shall be determined based on the anchor inclination. The horizontal anchor spacing and anchor capacity shall be selected to provide the required total anchor force. The vertical wall elements shall be designed to resist all horizontal earth pressure, surcharge, water pressure, anchor and seismic loadings as well as the vertical component of the anchor loads and any other vertical loads. Supports may be assumed at each anchor location and at the bottom of the wall if the vertical element is extended below the bottom of the wall. The stresses in and the design of the wall facing shall be computed in accordance with the requirements of Article 5.6.6. All components of the anchored wall system shall be checked for the various earth pressure distributions and other loading conditions which will exist during the course of construction. 5.7.6.2

Anchor Design

Anchor design shall include an evaluation of the feasibility of using anchors, selection of an anchor system, es-

timates of anchor capacity, determination of unbonded length, and determination of corrosion protection requirements. In determining the feasibility of employing anchors at a particular location, consideration shall be given to the availability or ability to obtain underground easements, proximity of buried facilities to anchor locations. and the suitability of subsurface soil and rock conditions within the anchor stressing zone.

Determination of the tlnbonded anchor length shall consider the location of the critical failure surface farthest from the wall, the minimum length required to Insure min-

imal loss of anchor prestress due to long-term ground movements, and the depth to adequate anchoring strata. As shown in Figure 5.7. IA, the unbonded (or free) anchor length should not be less than 15 feet and should extend beyond the critical failttre surface in the soil mass being retained by the wall. For granular soils or drained cohesive soils, the critical failtlre surface is typically assumed to be the active failure wedge which is defined by a plane extending upward from the base of the wall at an angle of 45 + ~‘I2 from the horizontal. Longer free lengths may be required for anchors in plastic soils or where critical failure surfaces are defined by planes or discontintiities with other orientations. Selection of an anchor inclination shall consider the location of suitable soil or rock strata, the presence of buried utilities or other geometric constraints, and constructahil-

ity of the anchor drill boles. The component of vertical load resulting from anchor inclination shall be included in evaluating the end bearing and settlement of vertical wall

elements. The minimum horizontal spacing of anchors should be either three times the diameter of the bonded zone or 4 feet, whichever is larger. tf smaller spacings are required, consideration can be given to differing anchor inclinations between alternating anchors.

5.7.7

Overall Stability

Refer to Article 5.2.2.3.

The required anchor forces shall be determined in accordance with Article 5.7.6.1. The ultimate anchor capacity per unit length may be preliminarily estimated using the guidelines presented in Tables 5.7.6.2A and 5.7.6.2B

for soil and rock, respectively. These guidelines are for preliminary design of straight shaft anchors installed in small diameter boles using a low grout pressure. Other anchor types and installation procedures could provide other estitnated ultimate anchor capacities. Final determination of the anchor capacity and required bond length shall be the responsibility of the anchored wall specialty contrac— br. The allowable anchor capacity for small diameter anchors may be estimated by multiplying the ultimate anchor capacity per unit length times the bonded (or stressing) length and dividitig by a FS of 2.5 for anchors in soil and 3.0 for anchors in rock. Bearing eletnet1ts for anchors shall be designed to maintain shear stresses in the

5.7.8

Corrosion Protection

Prestressed anchors and anchor heads shall be protected against corrosion consistent with the ground and ground water conditions at the site. The level and extent of corrosion protection shall be a function of the eround environment and the potential conseqtlences of an anchor failure. Corrosion protection shall be applied in accordance with Section 6 of Division Il—Ground Anchors.

5.7.9

Anchor Load Testing and Stressing

All anchors shall be tested in accordance with Section 6 of Division II Ground Anchors, Article 6.5.5. Testing and Stressing.

134

5.7.9

HIGHWAY BRIDGES

TABLE S.7.6.2A

Presumptive Ultimate Values of Load Transfer for Preliminary Design ofAnchors in Soil Modified after Cheney (1982)

Soil 1’~’pe Sand and Gravel

Sand

Sand and Silt

Silt-clay Mixture with Minimum LL, P1, and LI Restrictions, or Fine Micaceous~2~ Sand or Silt Mixtures (t) Values corrected for overburden pressure. (2) The

Relative Density/ Consistencytt~ Loose Medium dense Dense Loose Medium dense Dense Loose Medium dense Dense Stiff Hard

Estimated Ultimate Transfer Load (kips/lineal foot) 10 15 20 7 10 13 5 7 9 4 4

presence of mica tends to increase the volume and compressibility of sand and soft deposits due to bridging action

and subsequent flexibility under increased pressures. TABLE 5.7.6.2B Presumptive Ultimate Values of Load Transfer for Preliminary Design of Anchors in Rock Modified after Cheney (1982)

Rock Type

Estimated Ultimate Transfer Load (kips/lineal foot)

Granite or Basalt Dolomitic Limestone Soft Limestone

40

Sandstone

30

Slates and Hard Shales Soft Shales

25 10

5.8

50 30

MECHANICALLY STABILIZED

EARTH WALL DESIGN 5.8.1

Structure Dimensions

MSE walls shall be dimensioned to ensure that the minimum factors of safety required by Article 5.5.5 are satisfied. The following additional minimum factors of safety shall be satisfied:

Criterion Pullout resistance Ultimate bearing capacity

Factor of Safety =1.5

=2.0

Soil reintorcement length should be as a minimum approximately 70 percent of the wall height (as measured from the leveling pad) and not less than 8 feet for both strip- or grid-type reinforcement. The reinforcement length should be uniform throughout the entire height of the wall, unless substantiating evidence is presented to indicate that variation in length is satisfactory. External loads such as surcharges will increase the minimum reinforcement length. The minimum embedment depth of the bottom of the reinforced soil mass, which is the same as the top of the leveling pad, shall be based on bearing capacity, settlement, and stability requirements determined in accordance with Articles 5.2.2.1, 5.2.2.2, 5.2.2.3, 5.5.5, and pertinent portions of Section 5.8, including the effects of frost heave, scour, and proximity to slopes A minimum horizontal bench 4 feet wide shall be provided in front of walls founded on slopes. For walls constructed along rivers and streams, foundation depths must be established at a minimum of 2 feet below potential scour depth as determined in accordance with Article 5.3.5. 5.8.2

External Stability

Stability computations shall be made by assuming the reinforced soil mass to be a rigid body. The coefficient of active earth pressure, Ka, used to compute the horizontal force resulting from the random backfill behind the rein-

5.8.2

135

DIVISION I—DESIGN

Figures 5.8.2A, 5.8.2B, and 5.8.2C illustrate external stability equations for walls with horizontal backslope and inclined backslope, respectively. The equivalent height, H,, of an MSE structure with inextensible reinforcements supporting a slope shall be taken as the height measured to the point where the potential failure plane (line of maximum tension) intersects the ground surface, as shown in Figure 5.8.4. IA. If a break in the slope behind the wall facing is located horizontally within two times the height of the wall (2H), a broken

forced zone and other loads shall be computed on the basis of the friction angle of the random backfill. In the absence of specific data, a maximum friction angle of 30 degrees should be used. The limitation also applies when determining the coefficient of sliding friction at the wall base. Passive pressures shall be neglected in stability computations. The active earth pressure coefficients for random backfill shall be computed as shown in Figure 5.5.2B, with

= 13.

Horizontal Bocl~slooe WBti Tr~ff:c Sur~horae

q

ASSUMED .~ MAXIMUM j I t I I I SEARING STRESS S OVERALL STASIUTY. FFTTTT ASSUMED F~R OVERTURNING ~ SUDING & PLLLOUT RESISTANCE

COMPS. RAJ~M FILL

REINFORCZD

SOIL MASS 00-

H

——

.4-

VI •~HL

0-

F~sqHK0 F1 ‘14~l~K0

4-

c%J

0-

-S

I-

L ~0•7M

I.

.1

SAFFIY FACTOR AGAiNST aSIERTURWNG (MOMENTS ABOUT POINT O)~ Z Moments Resistino- (Mr) VI (L/Z) ‘.6 B S.F. lola Z Moments Overturning (Mo) SAFETY FACTOR AGAINST SLIOING: (VI) Ton ~ FI+FZ

S.F. CS) L~ Hor~oatal Force(s) ?*orizontol Resisting Driving Force(s) • a

>

IS

FrIction Mgl. of BaclcfiII or Foundatian~ whlchrnr I. lowest. L

2,

Mr-Mo

R

L

6

where: a u eccentricIty q u troffic surcharge

R=V1

If Mr=V1.~.(dO0d loaE

RuVj4-~L

If

Ntu(Vl4-~L)~-(dOOdlOGd+ live load surcharge)

FIGURE 5.8.2A Horizontal Backslope with Traffic Surcharge

HIGHWAY BRIDGES

136

5.8.2

SLOPING d6

6

h-H

h

H

q

qp

IE~

L~O.Th

SAFETY FACTOR AGAINST OVERTURNING (MOMENTS ABOUT POINT O) Z Moments Resisfino (Mi) V1 (L/2)+V2 ~ ~z.o Motne*it Overturning (Mo~

FH(h/3)

SAFETY FACTOR AGAINST SLIDENG: ~ Haizontal Resistlno Face(s) Horuwuol Oriviz~g Force(s) • •

R Tan~ FH

Friction Angle at BackfIll or Fowidataon~ ~icheverI. lowest.

• 2

when:

e V a— L-2* R

R em Eccentricity

Ru Resultant .f vertlwl forces Vj + ~‘2i~V

FIGURE S.8.2B Sloping Backfill Case back slope design (AREA. method) may be used, as illustrated in Figure 5.8.2.C. The minimum L/II ratio for reinforcement shall be 0.7. For calculations of mass stability, the continuous traftic surcharge loads shall be deemed to act at the end of the reinforced ,one.

For structures loaded with sloping surcharges, general stability analyses should be performed in accordance with

Article 5.2.2.3.

5.8.3

Bearing Capacity and Foundation Stability

Allowable bearing capacities for MSE walls shall be computed using a minimum factor of safety of 2.5 I’or Group I loading applied to the calculated ultimate bearing capacity. A lesser F.S.. of 2.0. could be used ifjustitied by a geotechnical analysis. The width of the footing for ultimate bearing capacity calculations shall be the length of the reinforcement calculated at the foundation level. The

5.8.3

137

DIVISION I—DESIGN

2H

I

Fr = l/2~h2 k,a

h

I

0i L

~‘

0.7H

Fr cos (I) = Fr sin CI) FOR INFiNITE SLOPE I =

=

K 0 FOR RANDOM FiLL (SEE FIGURE 5.5.2B~

SAFETY FACTOR AGAINST OVERTURNING (MOMENTS ABOUT POINT 0): S.F. (0)

=

E MOMENTS RESISliNG (Mr) ~ MOMENTS OVERTURNING (Mo)

_

‘w~

(L/2)

+

V2(2L/3) Fh (h/3)

+

Fy(L) =2.0

SAFETY FACTOR AGAINST SUDING:

S.F. (5) =

EHORIZONTAL RESISTING FORCE(s) E HORIZONTAL DRIVING FORCE(s)

_

R tan • Fh

=1.5

• = FRICTION ANGLE OF BACKFiLL OR FOUNDATiON. WHICHEVER IS LOWER. L

WHERE:

Mr—Mo R

~

e = ECCENTRICITY;

R

L—2e

R = RESULTANT OF VERTICAL FORCES—V1

FIGURE 5.8.2C Broken Back Backfill Case

+ V2

+

Fv

138

5.8.3

HIGHWAY BRIDGES

location of the resultant center of pressure shall be as stated in Article 5.5.5. Bearing pressures shall be computed using the Meyerhof distribution, which considers a uniform base pressure distribution over an effective width of footing B’ = L 2e. Overall slope stability factors of safety, of which the —

retaining wall may only be part, shall conform to the requirements of Article 5.2.2.3.

5.8.4

Internal Stability

5.8.4.1

two zones, the active and resistant zones. The failure surface shall be assumed to be bilinear as shown in Figure 5.8.4.1A. The horizontal stress, 5H. at each reinforcement level shall be computed by multiplying the vertical stress, s~, by an earth pressure coefficient, K. The vertical stress, S~, at each level of reinforcement shall consider the local equilibrium of all forces to that level only, and shall be computed using a uniform base pressure distribution over an effective width, as specified in Article 5.8.3. Structures shall be designed using K K 0 at the top of the structure and decreasing linearly to K Ka at 20 feet (Figure 5.8.4.lA). Below a 20-foot depth, K Ka shall be used. Assume the earth pressure coefficients of K, and K0 remain the same regardless of the external loading conditions. The values of Ka and K0 shall be computed as follows:

=

Inextensible Reinforcements

=

Internal stability of structures constructed with metallic strip or grid reinforcements shall be analyzed by considering that the in-situ reinforced zone can be divided in

K0

=

K0

T

H/2

H1

I

I

I— K

H1

=

E+

L~0.7H

—I

tan

B x .JH (1-.3tanp)

FIGURE 5.8.4.IA.

Determination of Failure Plane Location and Earth Pressure Coefficients

for Inextensible Reinforcements

5.8.4.1

DIVISION I—DESIGN K,

=

2(45

tan

—

(5.8.4.1-1) (5.8.4.1-2)

Alternately, the horizontal stresses at each reinforcing level may be computed using structure stiffness concepts as outlined in FHWA-RD-89-043.

The maximum friction angle used for the computation of horizontal force within the reinforced soil tnass shall be unless the specific project select backfill is tested for frictional strength by triaxial or direct shear testing methods, AASI-ITO T 234-74 and T 236-72. respectively. Live loads shall be treated as uniform surcharge loads actilig just beyond the reinforced soil mass for stability calculations and extending over the reinforced mass for maximum stress calculations. 340,

139

In the absence of pullout test data for ribbed reinforcing strips in backfill materials conforming to Division II, MSE backfills, a maximum value of the apparent coefficient of friction, f*, of 2.0 or less shall be used at ground level, decreasing linearly to a value equal to tan ~. at a depth of 20 feet, where ~ is the friction angle of the back-

fill within the reinforced volume. For smooth steel reinforcing strips, the apparent coefficient of friction shall be constant at all (lepths and can be evaluated by the following relation:

= tanqi

tensions induced by vertical or hon zontal line loads, or by point loads shall be added by superposition to the tensile forces induced by the reinforced wall fill soil and the re— a ined backfill. The met hod of ci m putat ion shall assLiifl e an Ltnvieldine ricid wall r()t~~tit~g about its toe. The value of K, in the reinforced soil mass is assumed to be independent of all external loads except sloping fi I Is. The maximum friction angle used for the compittation of horizontal stress within the reinforced soil mass, coin— posed of select backfill, shall be 340 in the absence of backfill specific tests. Where site-specific tests are perfornied, the soil strength shall be evaluated at residtlal stress levels.

lation for ultimate pullout capacity is:

The ultimate pullotit capacity of ribbed or smooth steel

= N, yZnAh

(5.8.5-3)

In the absence of pullout data for site specific backfills. the factor N 1, shall be taken as a function of depth as shown in Figure 5.8.5A. For end steel reinforcements with transverse spacine

less than 6 inches. the ultimate pullotIt capacity shall be calculated using the following expression:

PI.

=

2wlyZtan~f.1

(5.8.5-4)

The coefficient of resistance to (lirect sliding. f~. is a function of the open area of the grid. The xalue of fd varies from 0.45 for continuous sheets to 0.8 and must be determined experimentally for each gni(l geometry. For polymeric reinforcement, equation 5.8.5-4 is applicable when f~ is developed (‘or a range of normal stresses in accordance with GRI-GG-5. The coefficient f,,. obtained experimentally. may. be I united by’ the Li in it State Tensile Load fT1 ) for the product. as defitied in Article 5.8.7.2. The pullout resistance shall be checked at each level against pullout failure. Only the ef’f~ective pullout length which extends beyond the theoretical foilure surfaces shall be Lised in this computation.

The minimttm leneth in the resistant zone shall be 3 feet. The reinforcement length at all levels shall be equal. Minimum total length shall be 8 feet.

5.8.6

5.8.5 Pullout l)esign Parameters

(5.8.5-2)

For grid steel reinforcing systems with transverse bar

P,..

ineric reinforcements shall be analyzed using a tie-back wedge method approach. It is assumed that the full shear strength of the reinforced till is mobilized and active lateral earth pressures are developed. The assumed failure plane is defined by the Rankine active earth pressure zone defined by a straight line passing through the wall toe and oriented at an angle of 450 —r- ~‘/2 from the horizontal for both horizontal and sloping backfill conditions. The tensile force in the reinforcement is a function of the vertical stress induced by gravity’, uniform normal surcharge and active thrust mLtltiplied by K,~ Rein forcement

0.4

spacings of, or greater than. 6 inches. the generalized re-

5.8.4.2 Extensible Reinforcements Internal stability for structures constructed with poly—

‘~

Design Life Requirements

5.8.6.1

Steel Reinforcement

reinforcing strips shall be calculated using the following relationship:

f* y/A

(5.8.5-I)

Steel reinforcement elements in MSL walls shall be tIe— signed to have a corrosion—resistance durability to ensure a minimum design life of 75 years for permanent strtic— tures. Designated critical structures should be designed

5.8.6.1

HIGHWAY BRIDGES

140

Np —

PASSIVE RESISTANCE FACTOR

10

15

20

30

40

0 tIJ

“I

w

~6.

10

9-

z

LaJ

2 w 4.)

I&J

NOTE Valid for bac)cfill soils with a minimum (~) angle of

0 I-

34 degrees. 9-

a.

Lbi

0

50

FIGURE 5.8.5A

Mesh Reinforcement Pullout Factors

tor a 1(X)-year service life. The allowable reinforcement tension should be based on maintaining allowable material stresses to the end of the 75- or 100-year service life. The required sacrificial thickness must be provided in addition to the required structural reinforcement thickness to compensate for the effects of corrosion. The structural design of galvanized steel soil reinforcements and connections shall be made on the basis of a thickness, E. defined as follows: E~ =E,—E,

(5.8.6.1 - I)

formance to the requirements of AASHTO M 284. They can be considered in lieu of galvanization. 5.8.6.2

Polymeric Reinforcement

The durability of polymeric reinforcements is influenced by time, temperature, mechanical damage, stress

levels, microbiological attack and changes in the molecular structure by radiation or chemical exposure. The effects of aging, chemical and biological exposure are highly dependent on material composition, including

resin type, grade and additives, manufacturing process. For structural design, sacrificial thicknesses shall be

computed l’or each exposed surf’ace as f’ollows: Galvanization loss

Carbon steel loss

= IS pmlyear for first 2 years = 4 pm/year for subsequent years = 12 pm/year after zinc depletion

Corrosion-resistant coatings, if specified, shall be of the electro-statically applied. resin-bonded epoxy type, with minimum application thicknesses of 16 mils in con-

and final product physical structure. Product-specific

studies to determine the effects of these durability factors shall be carried out prior to use. Studies should include an evaluation of, but not be limited to, the effects of aging of the microstructure, chemical attack, microbiological at-

tack, environmental stress cracking, hydrolysis. temperature effects, plasticization, and any possible synergism between individual factors. Results from these studies shall be incorporated into durability reduction factors to the L.imit State Tensile Load T

1.

5.8.6.2

141

DIVISION I—DESIGN

The effect of construction damage on the reinforcement shall be determined from the results of full-scale

sis and variations in the manufacturing process as well as

construction damage tests using fill materials and con-

extrapolated to the required design life.

struction procedures representative of the site conditions. The effect of construction damage tests shall be incorporated into an additional construction damage reduction

factor to the Limit State Tensile Load T1. For these evaluations, the specified design life shall be

a minimum of 75 years and assumed critical in-ground service 0F. the Designated structures

the effects of construction damage shall be evaluated and The allowable reinforcement tension T,, shall be the lesser of the following two determinations: • Limit state determination: The allowable long-term reinf’orcement tension based on limit state criteria is:

temperature shall for be a70100-year service life. shall be designed T=

5.8.7

T/(FD

‘

FC’ FS)

(5.8.7.2-I)

Allowable Stresses

5.8.7.1

Steel Reinforcements

The allowable tensile stress for steel reinforcements and connections shall be in accordance with Article 10.32. For end reinforcing members, the allowable tensile stress shall be reduced to 0.48F\. Transverse and longitudinal grid members shall be sized in accordance with ASTM A-185. The horizontal force used to design the connections to the panels may be taken as no less than 85 percent of the maximum calculated force, except for the lower one-half of the structure where it shall be 100 percent. 5.8.7.2

Polymeric Reinforcements

Polymeric materials exhibit creep (time and temperature dependent) behavior. I ong-term stress-strain-time behavior of the reinforcement shall be (letermined f’rom results of controlled laboratory creep tests condtincted for a minimum duration of 10.000 hours for a ranm~e of load levels on samples of the finished product in accordance with ASIM I) 5%1~9~ Samples shall be tested in the direction in which the load will be applied in use in either a confined or uneonfined mode. Results shall be extrapolated to the required (lesign life using procedures outlined in ASTM D 2837 (ASTM. 1989). From these tests the followine shall be determined: • The hiehest load level at which the log time creepstrain rate continues to decrease with time within the required lifetime and no failure either brittle or due— tile can oceLir. This value shall be termed the Limit State Tensile Load, (lesignated asT 1. • The tension level at which total strain is not expected to exceed 5 percei~t within the (lesien lifetime. This value of load shall be desienated T~. the Serviceability State Tensile Load. The effects of acme, chemical and biological exposure. environmental stress craekin~. stress relaxation. hydroly-

where FS is an overall factor of safety to account for uncertainties in structure geometry, fill properties. reInforcement manufacturing variations and externally applied loads. The minimum FS shall be taken as 1.78. FD and FC shall be determined by tests. • Serviceability state determinations: ‘rhe allowable long—term reinforcement tensioti based on serviceability state criteria is:

= TJFC 5.8.8

‘

El)

(587

~)~))

1)rainage

MSF walls in cut areas and side-hill fills with established ground water levels shall be constructed with drainage blankets in back of and beneath the reinforced zone. Internal drainage measures shall be considered for all structures to prevent saturation of the reinforced back— till or to intercept any surface flows containing aggressive elements such as deicing chemicals. For MSE walls supporting roadways which are chemically deiced in the winter, an impervious membrane shall be placed below the pavement and just above the tirst row of reinforcements to intercept any flows containine deicinc chemicals. The membrane shall be sloped to drain away from the facing to an intercepting longitudinal drain outletted beyond the reinforced zone. 5.8.9

Special Loading Conditions

Concentrated line loads shall be incorporated into the internal design by using a siinplitied uniforin vertical dis— tribut ion of 2 x’ertical to I horizontal to determine the vertical component of stress with depth within the reinforced soil mass. Traffic loads shall be considered in accordance with

the criteria outlined in Article 3.20.3. For structures along rIvers and canals. a minimum dif— ferential hydrostatic pressure equal to 3 feet of water shall be considered for design. This load shall he applied at the hieh-water level. Effective unit weiehts shall be tised in

142

the calculations for internal and external stability beginning at levels just below the application of the differential

hydrostatic pressure. Parapets and traffic barriers, constructed over or in line with the front face of the panels shall be designed to resist

overturning moments by their own mass. Base slabs shall not have any transverse joints except construction joints. The

5.8.9

HIGHWAY BRIDGES

upper row of soil reinforcement shall be structurally

The inertial force (PiR) shall be taken to act simultaneously with one-half the dynamic horizontal thrust ~AE•,

computed using the pseudo-static Mononabe-Okabe method, and applied at 0.6 H2 above the base on the back

surface of the effective mass. Factors of safety against sliding and overturning failure under combined loading may be reduced to 75 percent of the factors of safety defined in Article 5.5.5.

sized to resist an additional horizontal load of 2,000 pounds per linear foot of wall. A minimum junction slab

length of 20 feet shall be used, joined to adjacent slabs with shear dowels. The full reinforcement length shall be considered effective in resisting the 10 kip impact horizontal load and shall be distributed to the reinforcement over a 20-foot junction slab length.

Parapet reinforcement shall be in accordance with Artide 2.7. The anchoring slab shall be strong enough to resist the ultimate strength of the standard parapet. Flexible post and beam barriers~, when used, shall be placed at a minimum distance of 3 feet from the wall face, driven 5 feet below grade, and spaced to miss the reinforcements. The upper two rows of reinforcement shall be designed for an additional horizontal load of 300 pounds

5.8.10.2

Internal Stability

Reinforcements shall be designed to withstand horizontal forces generated by the internal inertia force (P) in addition to the static forces. The total inertial force P, per unit length of structure shall be considered equal to the mass of the active zone times the maximum wall acceleration coefficient ~ This inertial force shall be distributed to the reinforcements proportionally to their resistant areas as follows: Tmd=PI

X

per linear foot of wall. 5.8.10

Seismic Design

5.8.10.1

External Stability

in addition to static forces, the horizontal inertial force (PIR) acting simultaneously with 50 percent of the dynamic horizontal thrust (PAk). The dynamic horizontal PAm:

(5.8.10.2-I)

(b;Lei ‘SHi)

For seismic loading conditions, values of f*, N~ and ~ may be reduced up to 80 percent of the values used for static design. Factors of safety under combined static and

Stability computations shall be made by considering,

thrust

(b~Lei/SHi N

shall be evaluated using the pseudo-static

seismic loads for pullout and breakage of reinforcement may be reduced to 75 percent of the factors of safety used for static loading.

5.8.11

Structural Requirements

Mononabe-Okabe method and shall be applied to the hack

surface of the reinf’orced fill at a height of 0.6H from the base and the horizontal inertial force at the mid-height of the structure. Values of P,~ and ~lR for structures with horizontal backfill, may be determined using the following: A~~= (1.45

—

A)A

(5.8.10.1-I)

2

PAF

= 0.375A,~yH

PiR

0.5AmYH2

Panels shall be designed to resist the horizontal f’orces calculated according to Articles 5.8.4.1 or 5.8.4.2. Reinforcement shall be provided to resist the average

loading conditions for each panel. As a minimum, temperature and shrinkage steel shall be provided. Epoxy coating for corrosion protection of panel reinforcement

where salt spray is anticipated is recommended.

(5 .8. 10. 1-2)

(5.8.10.1-3)

5.9

PREFABRICATED MODULAR WALL DESIGN

For structures with sloping backfills, the inertial force (PR) shall be based on an ef’fective mass having height H

2

5.9.1

Structure Dimensions

and a base width equal to 0.5 H~ determined as follows: Prefabricated modular walls shall be dimensioned It, =H+ Tan.13x0.SH -

(l—0.5Tan.13)

(5.8.10.1-4)

to ensure that the applicable factors of safety outlined in Article 5.5.5 are satisfied.

5.9.1

143

DIVISION I—DESIGN

Minimum embedment and scour protection shall satisfy the requirements of Article 5.8.1.

fective in resisting sliding motion. The value of ~ of the

5.9.2 External Stability

For structures loaded with sloping surcharges, refer to Article 5.2.2.3 regarding overall stability analysis of slopes.

foundation soils shall be used in these computations.

Stability computations shall be made by assuming that 5.9.3

the system acts as a rigid body.

Bearing Capacity and Foundation Stability

Lateral pressures shall be computed by wedge theory using a plane surface of sliding (Coulomb theory). Where

Allowable bearing capacities for concrete ITiodular systems shall be computed using a minimum factor of safety

the rear of the prefabricated modular systems forms an irregular surface (stepped modules), pressures shall be computed on an average plane surface drawn from the

of 3 for Group I loading applied to the ultimate bearing capacity or to a bearing capacity obtained in accordance

lower back heel of the lowest module to the upper rear

with Articles 4.4.7 and 4.4.8.

heel of the top module, as shown in Figures 5.9.2A and 5.9.2B.

Footing loads shall be computed by assuming that dead loads and earth pressure loads are resisted by point supports per unit length, at the rear and front of the modules

The following wall friction angles, 6. shall be used unless more exact coefficients are demonstrated:

(a)

(b)

(c)

Case Significant vibrations of backfill or modules settling more than backfill Continuous pressure surface of precast concrete (uniform width modules) Averaged pressure surface (stepped modules)

Wall Friction Angle (8)

0

or at the location of the bottom legs. For modules supported on integrally cast legs, the reactions shall be similarly calculated.

For this computation, a minimum of 80 percent of the soil weight inside the modules shall be considered effective. If foundation conditions require a footing tinder the total area of the module, 100 percent of the soil weight inside the modules shall be considered.

The overall slope stability condition, of which the retaining wall may only be part, shall be evaluated in accor1 /24

dance with Article 5.2.2.3.

3/4~

5.9.4

Computations for stability shall be made at every module level. At each level, the required factors of safety with

respect to overturning shall be provided. The value of K~ used to compute the lateral thrust resulting from the random backfill and other loads shall be computed on the basis of the friction angle of the backfill behind the modules.

If sufficient amounts of structural backfill are used behind the prefabricated modules, a value of 340 may be used for 4. In the absence of specific data, a maximum friction angle of 300 shall be used. The coefficient of sliding friction at the wall base shall be the lesser of the coefficients of the backfill or the foundation soil. Passive pressures shall be neglected in stability computations.

Allowable Stresses

Prefabricated modular units shall be designed for developed earth pressures behind the wall and from pressures developed inside the modules. Rear face surfaces shall be designed for the difference of these pressures. Allowable stresses and reinforcement requirements for concrete modules shall be in accordance with Section 8. Inside pressures (bin) shall be the same for each module and shall not be less than as follows:

= yb

(5.9.4-I)

Concrete modules shall be designed for bending in both vertical and horizontal directions between their supports. Steel reinforcing shall be symmetrical on both faces

Computations for overturning stability shall consider that only 80 percent of the soil-fill unit weight inside the modules is effective in resisting overturning moments. In the absence of specific data, a total unit weight of 110 pounds per cubic foot shall be assumed. Computations for sliding stability may consider that

be in accordance with Article 10.32. The net section used for design shall be reduced in accordance with Article

100 percent of the soil-fill weight inside the modules is ef-

5.8.6.1.

unless positive identification of each face can be ensured to preclude reversal of units. Corners shall be adequately reinforced. Allowable stresses for steel module members shall

5.9.5

HIGHWAY BRIDGES

144

pie.aS P.’— ~KK0

a

FIGURE 5.9.2A

5.9.5

cog’ (6. e~

Lateral Earth Pressures for Prefabricated Modular Walls Case I—Continuous Pressure Surfaces

Drainage

Part C STRENGTH DESIGN METHOD LOAD FACTOR DESIGN

Prefabricated modular units in cut and side-hill fill areas shall be designed with a continuous subsurface drain placed at, or near, the footing grade and out-letted as required. In cut and side-hill fill areas with established or potential ground water levels above the footing grade, a continuous drainage blanket shall be provided and connected to the longitudinal drain system.

For systems with open front faces, a surface drainage system1~ shall be provided as needed above the top of the wall to collect and divert surface runoff and prevent cr0sion of the front face.

5.10

SCOPE

The provisions of this Part shall apply for the design of rigid gravity and semi-rigid gravity walls, and non-gravity cantilevered walls. The probabilistic LFI) basis of these specifications which produces an inter-related combination of load, load factor, and statistical reliability shall be considered when selecting procedures for calculating resistance. The pro-

5.10

145

DIVISION I—DESIGN

a

Ke •

1163

(84~)

FIGURE 5.9.2B Lateral Earth Pressures for Prefabricated Modular Walls Case Il—Irregular Pressure Surfaces

cedures used in developing values of performance factors contained in this Part are summarized in Appendix A of the Final Report for NCHRP Project 24-4 (Barker, et al., 1991). Other methods may be used if the statistical nature of the factors given above are considered, and are approved by the owner.

Cantilever Walls—Walls that resist the forces exerted on them by flexural strength. These walls consist of a concrete wall stem, a concrete slab, and possibly a shear key. Gravity Walls—Massive stone or concrete masonry walls which depend primarily on their weights to maintain stability. Only a nominal amount of steel is placed near the

exposed faces of these walls to prevent surface cracking 5.11

DEFINITIONS

Only terms relating to retaining walls are provided in this Section. Definitions for terms relating to foundation types and LFD design are given in Article 4.8.

due to temperature changes.

Retaining Walls—Structures that provide lateral support for a mass of soil and that owe their stability primarily to their own weights and to the weights of any soils located directly above its base.

5.11

HIGHWAY BRIDGES

146

Semi-gravity Walls—These walls are somewhat more slender than gravity walls and require reinforcement consisting of vertical bars along the inner face and dowels continuing into the footing. 5.12

NOTATIONS

—excessive vibrations caused by dynamic loadings, and —deterioration of element(s) of retaining structures. The limit state for settlement shall be based upon rideability and economy. The cost of limiting foundation movements shall be compared to the cost of designing the

Fr

= sliding resistance

superstructure so that it can tolerate larger movements, or

H H 1 K

= height of retaining wall

of correcting the consequences of movements through maintenance, to determine minimum lifetime cost. More stringent criteria may be established by the owner.

K0 N

= coefficient of earth pressure at rest = factored bearing pressure resultant

P

=

Pa

= active earth load

= =

factored horizontal load coefficient of earth pressure

lateral earth pressure

= lateral earth load P.

=

vertical earth load

= factored bearing capacity qmax

q.

y

maximum bearing pressure calculated using factored loads = surcharge loading = ultimate bearing capacity = reduction factor due to load inclination effect = nominal resistance = factored vertical load = distance to the point of action for lateral earth pressure =

Greek

y yeq 6

= = =

load factor coefficient (see Article 5.13.4) load factor coefficient for earth pressure load factor (See Article 5.13.4) equivalent fluid pressure angle of shearing resistance between wall and soil

wall displacement performance factor 5.13 LIMIT STATES, LOAD FACTORS AND RESISTANCE FACTORS All relevant limit states shall be considered in the design

to ensure an adequate degree of safety and serviceability. 5.13.1

Serviceability Limit States

Design of rigid gravity and semi-gravity walls, and nongravity cantilever walls shall consider the following serviceability limit states: —excessive movements of retaining walls and their foundations,

5.13.2

Strength Limit States

Design of rigid gravity and semi-gravity walls, and nongravity cantilever walls shall be checked against the strength limit states of: —bearing capacity failure, —lateral sliding, —excessive loss of base contact, —overall instability, and —structural failure. The limit state which governs the design depends on: —type and function of retaining structure, —eai’th pressures exerted on the wall by the retained backfill, —geometry of the ground and the structure, —strength of the ground, —ground deformability, —groundwater, and —swelling pressure in clay backfills. 5.13.3

Strength Requirement

Retaining walls and their foundations shall be proportioned by the methods specified in Article 5.14 so that their design strength exceeds the required strength. The required strength is the combined effect of factored loads for each applicable load combination stipulated in Article 3.22. The design strength is calculated for each applicable limit state as the nominal resistance, R0, multiplied by an appropriate performance (or resistance) factor, Procedures for calculating nominal resistance ~.

are provided in Article 5.1, and values of performance factors are given in Article 5.13.5.

5.13.4

Load Combinations and Load Factors

Retaining structures and their foundations shall be proportioned to withstand safely all load combinations stipu-

lated in Article 3.22 which are applicable to the particular site or wall/foundation type. Impact forces shall not be ineluded in retaining wall design. (Refer to Article 3.8.) Values of y and 13 coefficients for load factor design, as given in Table 3.22.1 A, shall apply to strength limit state considerations; while those for service load design (also given in Table 3.22.IA) shall apply to serviceability considerations.

5.13.5

Performance Factors

Values of performance factors for geotechnical design of foundations are given in Tables 4.10.6-I through 4.10.6-3, while those for structural design are provided in Article 8.16.1.2.2. If methods other than those given in Tables 4.10.6-1 through 4.10.6-3 are used to estimate the soil capacity, the performance factors chosen shall provide the same reliability as those given in Tables 4.10.6-1 through 4.10.6-3. 5.14 GRAVITY AND SEMI-GRAVITY WALL DESIGN, AND CANTILEVER WALL DESIGN 5.14.1

147

DIVISION I—DESIGN

5.13.4

Earth Pressure Due to Backfill

The provisions of Article 5.5.2 and 5.6.2 shall also apply to the load factor design of rigid gravity and semigravity walls, and nongravity cantilevered walls respectively; with the exception that the loads shall be factored according to the bottom half of Table 3.22.1 A when checking wall stability against bearing capacity, sliding and overturning. Vertical earth pressure due to the dead load of the backfill shall have an overall load factor, -y13~, of l.Oy. Lateral earth pressures on walls backfilled with cohesionless soils shall be designed using effective stresses.

Walls backfilled with cohesive soils shall be designed using equivalent fluid pressures. The backfill, whether cohesionless or cohesive, shall be well drained, so that no

water pressures act on the wall, and no significant pore pressures act in the backfill. The load factor for lateral earth pressures calculated using equivalent fluid pressures shall be the same as those calculated using effective 13m~ = I .3y). stresses (y

The y and 13~ coefficients specified for earth pressure in Table 3.22.1 A are applicable directly to active or at rest earth pressures. The resistance due to passive earth pressure in front of the wall shall be neglected unless the wall extends well below the depth of frost penetration, scour or other types of disturbance. Where passive pressure is assumed to provide resistance, the performance factor (~) shall be taken as 0.6.

5.14.2

Earth Pressure Due to Surcharge

In the design of retaining walls and abutments where traffic can come within a horizontal distance from the top of the wall equal to one-half the wall height, the lateral earth pressure shall be increased by a live load surcharge pressure equal to not less than 2 feet of earth (Article 3.20.3). Impact loads shall not be included in the design of abutments (Article 3.8.1). Vertical earth pressure induced by live load surcharge and dead load surcharge shall have overall load factors of l.67-y and l.13-y, respectively. Lateral earth pressure induced by live load and dead load surcharge shall have an overall load factor of l.3y. Where heavy static and dynamic compaction equipment is used within a distance of one-half the wall height behind the wall, the effect of additional earth pressure that may be induced by compaction shall be taken into account. The load factor for compaction-induced earth pressures shall be the same as for lateral earth pressures

5.14.3

Water Pressure and Drainage

The provisions of Articles 5.5.3 and 5.6.3 shall also apply to the load factor design of rigid gravity and semi-gravity walls, and nongravity cantilevered walls, respectively. The backfill, whether cohesive or cohesionless, shall be well drained so that no water pressures act on the wall and no significant pore pressures act in the backfill. If a thorough drainage system is not provided to dewater the failure wedge, or if its adequate performance cannot be

guaranteed, walls shall be designed to resist the maximum anticipated water pressure. For walls backfilled with cohesionless soils, the lateral earth pressure shall be calculated using buoyant unit weights below the groundwater level and multiplied by the load factor for lateral earth pressure. The wall shall be designed for these factored lateral earth pressures (‘y13m~) plus factored hydrostatic water

pressure (l.Oy). In the case of an undrained analysis of cohesive backfills, the lateral earth pressure shall be calculated using

equivalent fluid pressure, which inherently includes water pressure effects. The calculated lateral earth pressure shall then be multiplied by I .3-y. If the groundwater levels differ on opposite sides of the wall, the effects of seepage on wall stability and the po-

tential for piping shall be considered. Pore pressures behind the wall can be determined by flow net procedures or various analytical methods, and shall be added to the effective horizontal stresses when calculating total lateral

earth pressures on the wall. The effective lateral earth

148

5.14.3

HIGHWAY BRIDGES

pressure shall be multiplied by

13F

Y

(obtained from Table

5.14.6

Safety Against Soil Failure

3.22.IA) and the hydrostatic pressure shall be factored by

l.Oy, when designing the wall. 5.14.4

Seismic Pressure

The provisions of Article 5.6.4 shall apply to the load factor design of walls when considering earthquakes loads. 5.14.5

Gravity and semi-gravity walls, and cantilever walls shall be dimensioned to ensure stability against bearing capacity failure, overturning, and sliding. Where a wall is supported by clayey foundation, safety against deep-seated foundation failure shall also be investigated. Stability criteria for walls with respect to various modes of failure shall be as shown in Figures 5.14.6-I through 5. 14.6-3. 5. 14.6.1

Movement Under Serviceability Limit States

Bearing Capacity Failure

The movement of wall foundation support systems shall be estimated using procedures described in Article 4.11.3, 4.12.3.2.2. or 4.13.3.2.2, for walls supported on spread footings, driven piles, or drilled shafts, respec-

The safety against bearing capacity failure shall be investigated: (I) by using factored soil pressures which are uniformly distributed over the effective base area, if the wall is supported by a soil foundation (see Figures

tively. Such methods are based on soil and rock parame-

5.14.6-I and 5.14.6-2); or (2) by using factored soil

ters measured directly or inferred from the results of in situ and/or laboratory tests.

pressures which vary linearly over the effective base area. if the wall is supported by a rock foundation (see Figure 5.14.6-3). Retaining walls and their foundations are considered to be adequate against bearing capacity failure if the factored bearing capacity (taking into consideration the effect of load inclination) exceeds the maximum soil pressure (q~,~) determined using factored loads. Methods for

Tolerable movement criteria for retaining walls shall be developed based on the function and type of wall, an-

ticipated service life, and consequence of unacceptable movements. Tolerable movement criteria shall be established in accordance with Articles 4.11.3.5, 4.12.3.2.3,

and 4.13.3.2.3.

Earli Loe~ P, mid Ph bmed on .zpw4w~.. hr ~

wW~ dome 0.4 94

S~IIy Criteria

timed far bemliig ~

q

~7qg

~9~

=

c~

FIGURE 5. 14.6.1 Earth Loads and Stability Criteria for Walls with Clayey Soils in the Backfill or Foundation (After Duncan et al., 1990)

5. 14.6.1

149

DIVISION I—DESIGN

(b~ Fgm onVea1c~ Pimie 11veu~ Heel elWeE

(a) Fmwe on Wel

Earth Loads P~ Ed Phcsddd wIng Coulon Edwe elm preeewe meary ~er Pe eulmelad wingjudomnient. wet dowence hr movement af hencE relitve te wed.

y.O.494 StabilIty CrIteria

Ueed hrbesing cqieny diedc

q

Fed Sewing Cqmnty

= 0R1 q~,

N

FIGURE 5.14.6-2 Earth Loads and Stability Criteria for Walls with Granular Backfills and Foundations on Sand or Gravel (After Duncan et al., 1990)

Earth H

Loads

Ph besd an i-rest pressawe P, estimated using judgment y.0.4 H

t

N

Stability C.ltula

Limed hr —

N FIGURE 5.14.6-3

eqadit, diedi

Sewing Cq.dty qFeinted~R1q~

Earth Loads and Stability Criteria for Walls with Granular Backfills and Foundations on Rock (After Duncan et al., 1990)

150

5.14.6.1

HIGHWAY BRIDGES

calculating factored bearing capacity are provided in Artide 4.11.4 for walls founded on spread footings, and in

Hq Factored Hatizotml toed lactated Ve,*aI toed

Articles 4.12.3.3 and 4.13.3.3 for walls supported on dri-

ven piles or drilled shafts, respectively. 5.14.6.2

Sliding

Fadoted Sewing Cwediy q 1- 0R1q~,

.

Where the retaining wall is founded on a spread footing, safety against sliding shall be investigated using the procedures specified in Article 4.11.4.3. 5.14.6.3

Overturning

toed

H ~j7edHe~rnWi V9 Factored Vedici toed

[7J LW~ ILJ>

q~exTf~~

The safety against overturning shall be ensured by limiting the location of the factored bearing pressure resultant (N) on the wall base. For walls supported by soil foundations, location of the factored bearing pressure resultant on the base of the wall foundation shall be within the middle half of the base. For walls supported by rock foundations, location of the factored bearing pressure resultant on the base of the wall foundation shall be within the middle three-quarters of the base.

5.14.6.4

Overall Stability (Revised Article 5.2.2.3)

The overall stability of slopes in the vicinity of walls shall be considered.

The overall stability of the retaining wall, retained

Factored

— —

- ~ H 9 Factored Hodzontei toed Vt FactoredVedical toed

Factored Sewing Capacity

~max~~

- 0R1 q~ Note maximum toe~eeeure q may exceed tie factored hewing capacity. q1

FIGURE

5.14.7-1

Contact Pressure Distribution

slope, and foundation soil or rock shall be evaluated for all walls using limiting equilibrium methods of analysis. The Modified Bishop, simplified Janbu or Spence methods of analysis may be used. Special exploration, testing and analyses may be required for bridge abutments or retaining walls constructed over soft deposits where consolidation and/or lateral flow of the soft soil could result in unacceptable long-term settlements or horizontal movements.

for Structural Design of Footings on Soil and Rock

5.14.7

5.14.7.3

Safety Against Structural Failure

The structural design of individual wall elements and wall foundations shall comply to the requirements given in Section 8. In the structural design of a footing on soil and rock at ultimate limit states, a linear contact pressure distribution determined using factored loads, as shown in Figure 5.14.7-1, shall be considered. The maximum pressure for structural design may be greater than the factored bearing capacity.

at Strength Limit States 5.14.7.1

Base of Footing Slabs

See Article 5.5.6.1. 5.14.7.2 Wall Stems See Article 5.5.6.2. Counterforts and Buttresses

See Article 5.5.6.3. 5.14.7.4 Reinforcement See Article 5.5.6.4. 5.14.7.5 Expansion and Contraction Joints See Article 5.5.6.5.

5.14.8 5.14.8

DIVISION I—DESIGN

Backfill

151

French drains placed at suitable intervals and elevations. In counterfort walls, there shall be at least one

Where possible, the backfill material behind all retaining walls shall be free draining, nonexpansive, noncorrosive and shall be drained by weep-holes and

drain for each pocket formed by the counterforts. Silts and clays shall, if possible, be avoided for use as backfill.

Section 6 CULVERTS 6.1

forced floor shall be used to distribute the pressure over the entire horizontal area of the structure. In any location

CULVERT LOCATION, LENGTH, AND WATERWAY OPENINGS

subject to erosion, aprons or cutoff walls shall be used at both ends of the culvert and, where necessary, the entire floor area between the wing walls shall be paved. Baffle walls or struts across the unpaved bottom of a culvert barrel shall not be used where the stream bed is subject to erosion. When conditions require, culvert footings shall be

Recommendations on culvert location, length, and waterway openings are given in the AASHTO Guide on Hydraulic Design of Culv’ert.v. 6.2

DEAD LOADS

reinforced longitudinally.

Vertical and horizontal earth pressures on culverts may be computed by recognized or appropriately documented analytical techniques based on the principles of soil mechanics and soil structure interaction, or design pressures

6.4

shall be calculated as being the result of an equivalent fluid weight as follows. 6.2.1

DISTRIBUTION OF WHEEL LOADS THROUGH EARTH FILLS

When the depth of fill is 2 feet or more, concentrated loads shall be considered as uniformly distributed over a square with sides equal to 1-3/4 times the depth of fill. 6.4.1

Culvert in trench, or culvert untrenched on yielding foundation

A. Rigid culverts except reinforced concrete boxes: 6.4.2 When such areas from several concentrations overlap, the total load shall be uniformly distributed over the area defined by the outside limits of the individual areas, but the total width of distribution shall not exceed the total width of the supporting slab. For single spans, the effect of live load may be neglected when the depth of fill is more

For vertical earth pressure— 120 pcf For lateral earth pressure— 30 pcf (2) For vertical earth pressure—120 pcf For lateral earth pressure— 120 pef B. Reinforced concrete boxes: (I) For vertical earth pressure— 120 pef For lateral earth pressure— 30 pef (I)

(2) For vertical earth pressure— 120 pcf

than 8 feet and exceeds the span length; f’or multiple spans it may be neglected when the depth of fill exceeds the dis-

For lateral earth pressure— 60 pcf C. Flexible Culverts: For vertical earth pressure— 120 pcf For lateral earth pressure— 120 pcf When concrete pipe culverts are designed by the Indirect

tance between faces of end supports or abutments. When the depth of fill is less than 2 feet the wheel load shall be distributed as in slabs with concentrated loads. When the calculated live load and impact moment in concrete slabs, based on the distribution of the wheel load through earth

fills, exceeds the live load and inipact moment calculated

i)esign Method of Article 17.4.5, the design lateral earth pressure shall be determined using the procedures given in Article 17.4.5.2.1 for embanknient installations and in Article 17.4.5.2.2 f’or trench installations.

6.2.2

according to Article 3.24, the latter moment shall be used.

6.5

Where the depth of till exceeds 2 feet, reinforccmi~ent to provide for the lateral distribution of concentrated loads is not required.

Culvert untrenched on unyielding foundation

A special analysis is required.

6.3

DISTRIBUTION REINFORCEMENT

FOOTINGS

6.6

Footings for culverts shall be carried to an elevation sufficient to secure a firm foundation, or a heavy rein-

DESIGN

For culvert design guidelines, see Section 17. 153

Section 7 SUBSTRUCTURES Part A GENERAL REQUIREMENTS AND MATERIALS 7.1

GENERAL

7.1.1

Definition

V

1

=

V2 =

A substructure is any structural, load-supporting component generally referred to by the terms abutment, pier, retaining wall, foundation or other similar terminology.

7.1.2

Active earth pressure coefficient (dim); (See Article 7.7.4.)

K, =

o’H

=

Vertical soil stress (ksf); (See Article 7.5.4.) Vertical stress due to footing load (ksf); (See Article 7.5.4.) Supplementary earth pressure (ksf); (See Article 7.5.4.)

Loads The notations for dimension units include the follow2. The ing: dim=dimensionless; ft =with foot;each and ksf = kip/ft dimensional units provided notation are presented for illustration only to demonstrate a dimensionally correct combination of units for the design procedures presented herein. If other units are used, the dimensional

Where appropriate, piers and abutments shall be designed to withstand dead load, erection loads, live loads on the roadway, wind loads on the superstructure, forces

due to stream currents, floating ice and drift, temperature and shrinkage effects, lateral earth and water pressures,

correctness of the equations should be confirmed.

scour and collision and earthquake loadings. 7.1.3

Settlement

Part B SERVICE LOAD DESIGN METHOD ALLOWABLE STRESS DESIGN

The anticipated settlement of piers and abutments should be estimated by appropriate analysis, and the effects of differential settlement shall be accounted for in

the design of the superstructure.

7.3

7.1.4

7.3.1

Foundation and Retaining Wall Design

driven pile and drilled shaft foundations and Section 5 for

moments acting about the weak axis and as piers for those acting about the strong axis. They may be pinned, fixed or free at the top, and are conventionally fixed at the base.

NOTATIONS

Short, stubby types are often pinned at the base to elimTiinate the high moments which would develop due to fixity. Earlier, more massive designs, were considered gravity types.

The following notations shall apply for the design of pier and abutnient substructure units:

e H K

= Width of foundation (ft) = Eccentricity of load from foundation centroid in = =

Solid Wall Piers

Solid wall piers are designed as columns for forces and

the design of retaining walls.

B

Pier Types

7.3.1.1

Refer to Section 4 for the design of spread footing,

7.2

PIERS

7.3.1.2

the indicated direction (ft) Height of abutment (ft) Coefficient of earth pressure varying from K,, at surface to K, at 20 feet (dim); (See Article 7.5.4.)

Double Wall Piers

More recent designs consist of double walls, spaced in the direction of traffic, to provide support at the continu155

156

ous soffit of concrete box superstructure sections. These

walls are integral with the superstructure and must also be designed for the superstructure moments which develop from live loads and erection conditions. 7.3.1.3

7.3.1.2

HIGHWAY BRIDGES

Bent Piers

Bent type piers consist of two or more transversely spaced columns of various solid cross sections, and these types are designed for frame action relative to forces act-

about the strong axis of the pier. They are usually fixed at the base of the pier and are either integral with the suing

perstructure or with a pier cap at the top. The columns

7.3.2.4

Facing

Where appropriate, the pier nose should be designed to effectively break up or deflect floating ice or drift. In these situations, pier life can be extended by facing the nosing with steel plates or angles, and by facing the pier with granite. 7.4

TUBULAR PIERS

7.4.1

Materials

Tubular piers of hollow core section may be of steel,

may be supported on a spread- or pile-supported footing,

reinforced concrete or prestressed concrete, of such cross

or a solid wall shaft, or they may be extensions of the piles

section to support the forces and monients acting on the

or shaft above the ground line.

elements. 7.4.2

7.3.1.4

Configuration

Single-Column Piers

Single-column piers, often referred to as “T” or “Ham-

merhead” piers, are usually supported at the base by a spread- or pile-supported footing, and may be either integral with, or provide independent support for, the superstructure. Their cross section can be of various shapes and

the column can be prismatic or flared to form the pier cap or to blend with the sectional configuration of the superstructure cross section. This type pier can avoid the complexities of skewed supports if integrally framed into the

superstructure and their appearance reduces the massiveness often associated with superstructures.

The configuration can be as described in Article 7.3.1

and, because of their vulnerability to lateral loadings, shall be of sufficient wall thickness to sustain the forces

and moments for all loading situations as are appropriate. Prismatic configurations may be sectionally precast or prestressed as erected.

7.5 ABUTMENTS 7.5.1

Abutment Types

7.5.1.1

7.3.2 Pier Protection 7.3.2.1

Collision

Where the possibility of collision exists from highway or river traffic, an appropriate risk analysis should be made to determine the degree of impact resistance to be

provided and/or the appropriate protection system.

Stub Abutment

Stub abutments are located at or near the top of approach fills, with a backwall depth sufficient to accoinmodate the structure depth and bearings which sit on the bearing seat.

7.5.1.2

Partial-Depth Abutment

Partial-depth abutments are located approximately at 7.3.2.2

Collision Walls

Collision walls extending 6 feet above top of rail are required between columns for railroad overpasses, and similar walls extending 2.35 feet above ground should be

considered for grade separation structures unless other protection is provided. 7.3.2.3

Scour

The scour potential must be determiiined and the design must be developed to minimize failure from this condition.

mid-depth of the front slope of the approach embankment. The higher backwall and wingwalls may retain till material, or the embankment slope may continue behind the backwall. In the latter case, a structural approach slab or end span design must bridge the space over the fill slope. and curtain walls are provided to close off the open area. Inspection access should be provided for this situation.

7.5.1.3

Full-Depth Abutment

Full-depth abutments arc located at the approximate front toe of the approach embankmemit. restricting the opening under the structure.

7.5.1.4

Integral Abutment

Integral abutments are rigidly attached to the superstructure and are supported on a spread or deep foundations capable of permitting necessary horizontal movements. 7.5.2

157

DIVISION I—DESIGN

7.5.1.4

Loading

Abutments shall be designed to withstand earth pressure as specified in Article 5.5 and 5.6, the weight of the abutment and bridge superstructure. live load on the superstructure or approach fill, wind forces and longitudinal f’orces when the bearings are fixed, and longitudinal forces dime to friction or shear resistance of bearings. The design shall be investigated for any combination of these forces which may produce the most severe condition of loading.

Integral abutments must be designed for forces generated by thermal movements of the superstructure. 7.5.2.1

Stability

holes with French drains placed at suitable intervals and elevations. Silts and clays shall not be used for backfill. 7.5.3

Integral Abutments

Integral abutments shall be designed to resist the forces generated by thermal movements of the superstructure against the pressure of the fill behind the abutment. Integral abutments should not be constructed on spread footings founded or keyed into rock. Movement calculations shall consider temperature. creep. and long-term prestress shortening in determining potential movements of abutments. Maximum span lengths. design considerations, details should comply with recommendations outlined in FHWA Technical Advisory T 5140.13 (1980) except where substantial local experience indicates otherwise. To avoid water intrusion behind the abutment, the approach slab should be connected directly to the abutment

(not to wingwalls), and appropriate provisions should be made to provide for drainage of any entrapped water.

Abutments shall be designed for the loading combination specified in Article 3.22. • Abutments on spread footings shall be designed to resist overturning (FS = 2.0) and sliding (FS = 1.5). Dead and live loads are assumed uniformly distributed over the length of the abutment between expansion joints. • Allowable foundation pressures and pile capacities shall be determined in accordance with Articles 4.4

and 4.3. • ihe earth pressures exerted by fill in front of the abutment shall be neglected. • Earthquake loads shall be considered in accordance with Article 3.21. • The earth pressures exerted by the fill material shall be calculated in accordance with Articles 5.5.2 and 5.6.2. • The cross section of stone niasonry or plain concrete abutments shall be proportioned to avoid the introduction of tensile stress in the material.

7.5.2.2

Reinforcement for Temperature

Exeept in gravity abutments, not less than 1/8 square inch of horizontal reinforcement per foot of height shall be provided micar exposed surfaces not otherwise reinforced to resist the formation of temperature and shrinkage cracks.

7.5.2.3

Drainage and Backlilling

The filling material behind abutments shall be free draining, nonexpansi~~e soil, and shall be drained by weep

7.5.4

Abutments on Mechanically Stabilized Earth Walls

Design of bridge abutment footings and connecting back wall, shall be based on bridge loading developed by service load methods and earth pressures on the back wall. Abutment footings shall be proportioned to meet the overturning and sliding criteria specified in Article 5.5.5 and for maximum uniform bearing pressures using an el’fective width of foundations (B — 2e). The maximum allowable bearing pressure shall be 4.0 ksf. The mechanically stabilized earth wall below the abutment footing shall be designed for the additional loads unposed by the footing pressure and supplemental earth pressures resulting from horizontal loads applied at the bridge seat and from the back wall. The footing load is assumed to

be uniformly distributed over the effective width of foundation (B 2e) at the base of the f’ooting and is dispersed —

with depth, using a slope of 2 vertical to I horizontal. The supplemental loads are applied as shears along the bottom of the footing, uniformly diminishing with depth to a point on the face of the wall equal to twice the effective width of the abutment footing (B — 2e). Horizontal stresses in abutment reinforced zones are caletilated by superposition as follows and as shown in

Figure 7.5.4A.

=

(YV

1K

+

(TV:K~ ~

(7.5.4-I)

The effective length used for calculations of internal stability under the abutment footing shall always be the length

7.5.4

HIGHWAY BRIDGES

158

FOOTING LOADS

SOIL LOADS ‘12=

.(~V—QydxL+qxL)

yd+q (surcharge)

-o

I

z

B—2e o~SOlL Where

e

=

of vertical bridge loads

2e

o~ BRIDGE o~BRlDGE = (L—2e’

B— 2e eccentricity

P

( Dvi ~) Where e’

= eccentricity (

Dvi @ mis.

of footing )

SUPPLEMENTAL LOADS

F -j

c..J

I

0’

Li H supplemental max. =

L—2e’ H max.

=

0v (soil

loads)

‘

K

+

av

(footing loads)’KA

+

0H

(supplemental loads)

FIGURE 7.5.4A Abutment Loads beyond the end of the footing or beyond a distance of 0.3(l-I+d) from the facing, whichever is less. The minimum distance from the center line of the bearing on the abutment to the outer edge of the facing shall be 3.5 feet. The minimum distance between the back face of the panel and the footing shall be 6 inches.

The abutment footing should be placed on a bed of com-

pacted coarse aggregate 3 feet thick when significant frost penetration is anticipated. Abutments shall not be constructed on mechanically stabilized embankments if anticipated differential settlements between abutments or between piers and abutments are greater than one-half the limiting differential settlements as shown in Figure 7.5.4B. This figure should be

7.5.4

159

DIVISION I—DESIGN

14.

12.

2.i

IC -

-Jw 8-

116. @2

zw

4

2-

0

25

50

75

100

125

SPAN LENGTh

~0

~S

200

(Fr)

FIGURE 7.5.4B Limiting Values of Differential Settlement Based on Field Surveys of Simple and Continuous Span Structures of Various Span Lengths, Moulton, et al. (1985)

used for general guidance only. Detailed analyses will still be required to address differential settlement problems.

For structures supporting bridge abutments, the maximtlm horizontal force shall be used for connection design throughout the height of the structure. The density, length. and cross section of the soil reinforcements designed for support of the abutment wall shall be carried on the wing walls for a minimum horizontal distance equal to 50 percent of the height of the abutment wall. In pile-supported abutments, the horizontal forces transmitted to the piles shall be resisted by their own lateral capacity or by additional reinforcement in the tipper portion of the structure. A minimum clear distance of 1 .5 feet shall be provided between the facing and piles. Piles shall be driven prior to wall construction and cased

through the fill if necessary. 7.5.5

Abutments on Modular Systems

Abutments seats constructed on modular units shall be designed by considering, in addition to earth pressures, the

supplemental horizontal pressures from the abutment seat

beam and earth pressures on the back wall. The top module shall be proportioned to be stable, with the required factor of safety, under the combined actions of normal and supplementary earth pressures. Minimum top module width shall be 6 feet. The center line of bearing shall be located a minimum of 2 feet from the outside face of the top precast tnodule. The abutment beam seat shall be supported and cast integrally to the top module. The front face thickness of the top module shall be designed for bending forces developed by supplemental earth pressures. Abutment beamseat loadings shall be carried to foundation level an(l shall be considered in the design of footings. Differential settlement restrictions in Article 7.5.4. shall apply. 7.5.6

Wingwalls

7.5.6.1

Length

Wingwalls shall be of sufficient length to retain the roadway embankment to the required extent and to furnish

7.5.6.1

HIGHWAY BRIDGES

160

Part C

protection against erosion. The wingwall lengths shall be

STRENGTH DESIGN METHOD

computed using the required roadway slopes.

LOAD FACTOR DESIGN 7.5.6.2

Reinforcement

Reinforcing bars or suitable rolled sections shall be spaced across the junction between wingwalls and abutments to tie them together. Such bars shall extend into the masonry on each side of the joint far enough to develop the strength of the bar as specified for bar reinforcement, and shall vary in length so as to avoid planes of weakness in the concrete at their ends. If bars are not used, an expansion joint shall be provided and the windwall shall be keyed into the body of the abutment.

7.6

GENERAL

The provisions of Article 7.1 through 7.5 shall apply to the load factor design of abutments with the exception that: (I) Article 7.5.2 on loading shall be replaced by the articles for loads, earth pressures and water pressures in Sections 5.13 and 5.14 for retaining walls, and (2) Article 7.5.2.1 shall be replaced by the articles for stability in Sec-

tions~~~.l3 and 5.14. Abutments shall be designed to withstand earth pressures., water pressures and other loads similar to the design of retaining walls.

Section 8 REINFORCED CONCRETE* Part A GENERAL REQUIREMENTS AND MATERIALS 8.1

= area of reinforcement in bracket or corbel re-

APPLICATION

sisting moment, sq. in. (Articles 8.15.5.8 and

8.1.1

General

8.16.6.8) A

8.1.2 a ah

= area of reinforcement in bracket or corbel resisting tensile force N, (N,,), sq. in. (Articles

depth of equivalent rectangular stress block (Article 8.16.2.7) = depth of equivalent rectangular stress block

= shear span, distance between concentrated load and face of support (Articles 8.15.5.8 and 8.16.6.8)

A

= effective tension area, in square inches, of

A~f

8.15.5.8 and 8.16.6.8) = area of tension reinforcement, sq. in. = area of compression reinforcement, sq. in. = area of reinforcement to develop compressive

A,k

T-sections (Article 8.16.3.3.2) = area of skin reinforcement per unit height

strength of overhanging flanges of I- and

in one side face, sq. in. per ft. (Article 8. 17.2. 1.3).

= total area of longitudinal reinforcement (Articles 8.16.4.1.2 and 8.16.4.2.1)

concrete surrounding the flexural tension reinforcement and having the same centroid as that reinforcement, divided by the number of

area of shear reinforcement within a dis-

A,

=

A,f

= area of shear-friction reinforcement, sq. in. (Article 8.15.5.4.3) = area of an individual wire to be developed or

tance s

bars or wires. When the flexural reinforcement consists of several bar or wire sizes, the

A,

number of bars or wires shall be computed as the total area of reinforcement divided by the

spliced, 8.30.2)

area of the largest bar or wire used. For calculation purposes, the thickness of clear concrete cover used to compute A shall not be taken greater than 2 in.

= area of an individual bar, sq. in. (Article 8.25.1) = area of core of spirally reinforced compres-

sq.

in.

(Articles

8.30.1.2

and

A1

= loaded area (Articles 8.15.2.1.3 and 8.16.7.2) = maximum area of the portion of the supporting surface that is geometrically similar to and concentric with the loaded area (Articles

b

=

8.15.2.1.3 and 8.16.7.2)

sion member measured to the outside diameter of the spiral, sq. in. (Article 8.18.2.2.2) A,,

A,

Notations

a,

A,

= gross area of section, sq. in. = area of shear reinforcement parallel to flexural tension reinforcement, sq. in. (Articles 8.15.5.8 and 8.16.6.8)

for balanced strain conditions, in. (Article 8.16.4.2.3)

Ab

A1,

5

The specifications of this section are intended for design of reinforced (non-prestressed) concrete bridge members and structures. Bridge members designed as prestressed concrete shall conform to Section 9.

= area of concrete section resisting shear transfer. sq. in. (Article 8.16.6.4.5)

width of compression face of member = perimeter of critical section for slabs and footings (Articles 8.15.5.6.2 and 8.16.6.6.2) = width of cross section at contact surface being investigated for horizontal shear (Article 8.15.5.5.3)

5Thc speciticaiioos of Section 8 are patterned afmer and are in generat conformity with the provisions of AC! Standard 3 t 8 for reinforced concrete design and its commentary. AC! 3 t8 R, pubtished by the American Concreme tnsiituic. 161

162

= web width, or diameter of circular section c

= tensile stress in reinforcement at service loads, psi (Article 8.15.2.2) = stress in compression reinforcement at balanced conditions (Articles 8.16.3.4.3 and

(Article 8.15.5.1.1) = distance from extreme compression fiber to neutral axis (Article 8.16.2.7)

8.16.4.2.3)

= factor relating the actual moment diagram

to an equivalent uniform moment diagram (Article 8.16.5.2.7) d

=

distance from extreme compression fiber to centroid of tension reinforcement, in. For computing shear strength of circular sections, d need not be less than the distance from extreme compression fiber to centroid of tension reinforcement in opposite half of memher. For computing horizontal shear strength of composite members, d shall be the distance from extreme compression fiber to cen-

h

= distance from extreme compression fiber to

centroid of compression reinforcement, in. = distance from centroid of gross section, neglecting the reinforcement, to centroid of tension reinforcement, in. = nominal diameter of bar or wire, in. = distance measured from extreme tension fiber to center of the closest bar or wire in inches.

For calculation purposes, the thickness of

k

fdh

clear concrete cover used to compute d, shall

not be taken greater than 2 in. = modulus of elasticity of concrete, psi (Article

8.7.1) = flexural stiffness of compression member

(Article 8.16.5.2.7) = modulus of elasticity of reinforcement, psi (Article 8.7.2) = average bearing stress in concrete on loaded area (Articles 8.15.2.1.3 and 8.16.7.1) = extreme fiber compressive stress in concrete

edh ~hb

M M

at service loads (Article 8.15.2.1.1) = specified compressive strength of concrete,

psi

Mb

= square root of specified compressive strength of concrete, psi = average splitting tensile strength of light-

weight aggregate concrete, psi f~

= fatigue stress range in reinforcement, ksi (Article 8.16.8.3) = algebraic minimum stress level in reinforce-

ment (Article 8.16.8.3) = modulus of rupture of concrete, psi (Article 8.15.2.1.1)

= extreme fiber tensile stress in concrete at service loads (Article 8.15.2.1.1) = specified yield strength of reinforcement, psi = overall thickness of member, in. = compression flange thickness of I- and T-

sections = moment of inertia of cracked section trans-

troid of tension reinforcement for entire composite section.

El

8.1.2

HIGHWAY BRIDGES

M,~r

formed to concrete (Article 8.13.3) I,= effective moment of inertia for computation of deflection (Article 8.13.3) = moment of inertia of gross concrete section about centroidal axis, neglecting reinforcement = moment of inertia of reinforcement about centroidal axis of member cross section = effective length factor for compression memhers (Article 8.16.5.2.3) = additional embedment length at support or at point of inflection, in. (Article 8.24.2.3) = development length, in. (Articles 8.24 through 8.32) = development length of standard hook in tensmon, measured from critical section to outside end of hook (straight embedment length between critical section and start of hook (point of tangency) plus radius of bend and one bar diameter), in. (Article 8.29) = ehb X applicable modification factor = basic development length of standard hook in tension, in. = unsupported length of compression member (Article 8.16.5.2.1) = computed moment capacity (Article 8.24.2.3) = maximum moment in member at stage for which deflection is being computed (Article 8.13.3) = nominal moment strength of a section at balanced strain conditions (Article 8.16.4.2.3) = moment to be used for design of compression member (Article 8.16.5.2.7) = cracking moment (Article 8.13.3) = nominal moment strength of a section = nominal moment strength of a section in the direction of the x axis (Article 8.16.4.3) = nominal moment strength of a section in the direction of they axis (Article 8.16.4.3) = factored moment at section

M~.

= = =

M=b

163

DIVISION I—DESIGN

8.1.2

factored moment component in the direction ofthex axis (Article 8.16.4.3) factored moment component in the direction of the y axis (Article 8.16.4.3) value of smaller end moment on compression member due to gravity loads that result in no appreciable sidesway calculated by conventional elastic frame analysis, positive if memher is bent in single curvature, negative if bent in double curvature (Article 8.16.5.2.4)

=

=

r

= =

s

= spacing of shear reinforcement in direction

s

= spacing of wires to be developed or spliced,

tional elastic frame analysis, always positive

S

(Article 8.16.5.2.4)

V

= span length, ft = design shear force

parallel to the longitudinal reinforcement, in.

= value of larger end moment on compression

member due to gravity loads that result in no

in.

appreciable sidesway calculated by conven-

M

2~

=

value of larger end moment on compression member due to lateral loads or gravity loads

v

=

that result in appreciable sidesway, defined

n N

by a deflection A, greater than fj1500, calculated hy conventional elastic frame analysis, always positive. (Article 8.16.5.2) — modular ratio of elasticity = E]E, (Article 8.15.3.4) = design axial load normal to cross section oc-

cuffing simultaneously with V to be taken as positive for compression, negative for tension and to include the effects of tension due to shrinkage and creep (Articles 8.15.5.2.2 and 8.15.5.2.3) N,

N ~,,

Ph

P.

design tensile force applied at top of bracket of corbel acting simultaneously with V, to be taken as positive for tension (Am’ticle 8.15.5.8) = factored axial load normal to the cross section occurring simultaneously with V, to be taken as positive for compression, negative for tension, and to include the effects of tension due to shrinkage and creep (Article 8.16.6.2.2) = factored tensile force applied at top of bracket or corbel acting simultaneously with V~, to be taken as positive for tension (Artidc 8.16.6.8) = nominal axial load strength of a section at balanced strain conditions (Article 8.16.4.2.3)

=

= critical load (Article 8.16.5.2.7) = nominal axial load strength of

a section at zero eccentricity (Article 8.16.4.2.1) nominal axial load strength at given eccen-

tricity = nominal axial load strength corresponding to

with bending considered in the direction of the x axis only (Article 8.16.4.3) ~

at section

(Article

8.15.5.1.1) design shear stress at section (Article 8.15.5.1.1) nominal shear strength provided by concrete (Article 8.16.6.1)

= permissible shear stress carried by concrete

(Article 8.15.5.2)

design horizontal shear stress at any cross

vdh

=

vh

= permissible horizontal shear stress (Article

section (Article 8.15.5.5.3)

8.15.5.5.3) = nominal shear strength (Article 8.16.6.1) =

V,h

=

=

=

nominal axial load strength corresponding to M,,5, with bending considered in the direction of the y axis only (Article 8.16.4.3) nominal axial load strength with biaxial loading (Article 8.16.4.3) factored axial load at given eccentricity radius of gyration of cross section of a compression member (Article 8.16.5.2.2)

=

nominal horizontal shear strength (Article 8.16.6.5.3) nominal shear strength provided by shear reinforcement (Article 8.16.6.1) factored shear force at section (Article 8.16.6.1)

= =

z

=

weight of concrete, lb per cu ft distance from centroidal axis of gross section, neglecting reinforcement, to extreme fiber in tension (Article 8.13.3) quantity limiting distribution of flexural reinforcement (Article 8.16.8.4)

c~ (alpha) = angle between inclined shear reinforcement =

c~f

and longitudinal axis of member angle between shear-friction reinforcement and shear plane (Articles 8.15.5.4 and 8.16.6.4)

~

(beta)

=

ratio of area of reinforcement cut off to total area of reinforcement at the section (Article 8.24.1.4.2)

13,

=

ratio of long side to short side of concentrated load or reaction area; for a circular concentrated load or reaction area, 8.15.5.6.3 and 8.16.6.6.2)

13, =

1.0 (Articles

164

load moment to maximum total load mo-

Design load—All applicable loads and forces or their related internal moments and forces used to proportion

ment, always positive

members. For design by SERVICE LOAD DESIGN, de-

= absolute value of ratio of maximum dead

13~ X

= ratio of depth of equivalent compression zone

sign load refers to loads without load factors. For design

to depth from fiber of maximum compressive strain to the neutral axis (Article 8.16.2.7) correction factor related to unit weight for concrete (Articles 8.15.5.4 and 8.16.6.4) coefficient of friction (Article 8.15.5.4.3) tension reinforcement ratio = A,/b4, A~/bd compression reinforcement ratio = AJbd

by STRENGTH DESIGN METHOD, design load refers to loads multiplied by appropriate load factors. Design strength—Nominal strength multiplied by a

=

p (mu) p (rho)

p

= = =

Ph

=

p.

= ratio of volume of spiral reinforcement to

reinforcement ratio producing balanced strain conditions (Article 8.16.3.1.1) total volume of core (out-to-out of spirals) of a spirally reinforced compression member (Article 8.18.2.2.2)

= =

reinforcement ratio used in Eqtiation (8-4) and Equation (8-48) moment magmiification factor for members

braced against sidesway to reflect effects of member curvature between ends of compression member = moment magnification factor for members

not braced against sidesway to reflect lateral drift resulting from lateral and gravity loads ~ (phi)

8.1.3

8.1.2

HIGHWAY BRIDGES

= strength reduction factor (Article 8.16.1.2)

Definitions

The f’ollowing terms are defined for general use in

strength reduction factor, ~. Development length—Length of embedded reinforcement required to develop the design strength of the reinforcement at a critical section. Embedment length—Length of embedded reinforcement provided beyond a critical section. Factored load—Load, multiplied by appropriate load factors, used to proportion members by the STRENGTH DESIGN METHOD.

Nominal strength—Strength of a member or cross section calculated in accordance with provisions and assumptions of the STRENGTH DESIGN METHOL) before application of any strength reduction factors. Plain reinforcement—Reinforcement that does not conform to the definition of deformed reinforcement. Required strength—Strength of a member or cross section required to resist factored loads or related internal moments and forces in such combinations as are stipulated in Article 3.22. Service load—Loads without load factors. Spiral reinforce~nent—Continuously wound reinforcement in the form of a cylindrical helix. Splitting tensile strength (U—Tensile strength of concrete determined in accordance with “Specifications for

Section 8. Specialized definitions appear in individual

Lightweight

Articles.

AASHTO M 195** (ASTM C 330).

Bracket or corbel—Short (haunched) cantilever that

projects from the face of a column or wall to support a concentrated load or beam reaction. See Articles 8.15.5.8 and 8.16.6.8. Compressive strengrim 0/ concrete (f,’ )—Speci fled compressive strength of concrete in pounds per square

inch (psi). Concrete, structural lightweight—A concrete containing lightweight aggregate having an air-dry unit weight as determined by “Method of Test for Unit Weight of Structural Lightweight Concrete” (ASTM* C 567), not exceed-

ing 115 pef. In this specification, a lightweight concrete without natural sand is termed “all-lightweight concrete” and one in which all fine aggregate consists of normal

weight sand is termed “sand-lightweight concrete.” Deformed reinforcement—Deformed reinforcing bars, deformed wire, welded smooth wire fabric, and welded deformed wire fabric.

Aggregates

for

Structural

Concrete”

Stirrups or ties—Lateral reinforcement fornied of individual units, open or closed, or of continuously wound reinforcement. The term “stirrups” is usually applied tc) lateral reinforcement in horizontal members and the term

“ties” to those in vertical members. Tension tie member—Member having an axial tensile

force sufficient to create tension over the entire cross section and having limited concrete cover on all sides. Examples include: arch ties, hangers carrying load to an overhead supporting structure, and main tension elements in a truss. Yield strength or yield poilmt (f

5)—Specified minimum yield strength or yield point of reinforcement in pounds per square inch.

8.2 CONCRETE The specified compressive strength, f., of the concrete for each part of the structure shall be shown on * *Stcjndc,rd SpeciJlcorion.s for Tn~n.sportation Alaterjals and Methods

*An)erican Society for Testing and Maicriats.

ofSampling and Testing.

8.2

DIVISION I—DESIGN

the plans. The requirements for f shall be based on tests of cylinders made and tested in accordance with Section 4— Division II

8.3.3 Designs shall not use a yield strength, f~, in excess of 60,000 psi. 8.3.4

8.3

165

Deformed reinforcement shall be used except that

plain bars or smooth wire may be used for spirals and ties.

REINFORCEMENT

8.3.1

The yield strength or grade of reinforcement shall be shown on the plans.

8.3.2

Reinforcement to be welded shall be indicated on the plans and the welding procedure to be used shall be specified.

8.3.5 Reinforcement shall conform to the specifications listed in Division II, Section 5, except that, for reinforcing bars, the yield strength and tensile strength shall correspond to that determined by tests on full-sized

bars.

Part B ANALYSIS

8.4

GENERAL

All members of continuous and rigid frame structures shall be designed for the maximum effects of the loads specilied iii Articles 3.2 through 3.22 as determined by the theory of elastic analysis.

8.6

STIFFNESS

8.6.1

Any reasonable assumptions may be adopted for computing the relative flexural and torsional stiffnesses of continuous and rigid frame members. The assumptions made shall be consistent throughout the analysis.

8.6.2 8.5

EXPANSION ANI) CONTRACTION

8.5.1

In general. provisions for temperature changes shall be made in simple spans when the span length exceeds 40 f’eet.

The effect of haunches shall be considered both in determining iTloinents and in design of members.

8.7

MODULUS OF ELASTICITY AND POISSON’S RATIO

8.7.1 8.5.2 In contincious bridges, the design shall provide for thermal stresses or for the accommodation of thermal movement with rockers, sliding plates, elastomeric pads, or other mean~. 8.5.3 The coefficient of thermal expansion and contraction for normal weieht concrete may be taken as 0.000006 per cleg F

The modulus of elasticity. E,, for concrete may be taken as w~’ 33 \/f” in psi for values of w, between 90 and 155 pounds per cubic foot. For normal weight eomv crete (w, = 145 pet). F. may be considered as 57,000\‘f’’. 8.7.2 The modulus of elasticity. E~. for non-prestressecl steel reinforcement may be taken as 29,000,000 psi.

8.7.3 Poisson’s ratio may be assumed as 0.2.

8.5.4

8.8

‘I’hermal and shrinkage coefficients for light— weieht concrete shall be determined for the type of light— xveight aggregate used.

8.8.1 The span length of members that are not bLiilt in— tegrally with their supports shall be considered the clear span plus the depth of the member but need not exceed the distance between centers of supports.

The coefficient of shrinkage for normal weight concrete may be taken as 0.0002. 8.5.5

SPAN LENGTH

166

8.8.2

HIGHWAY BRIDGES

8.8.2

In analysis of continuous and rigid frame members, distances to the geometric centers of members shall

be used in the determination of moments. Moments at faces of support may be used for member design. When fillets making an angle of 45 degrees or more with the axis of a continuous or restrained member are built monolithic

with the member and support, the face of support shall be considered at a section where the combined depth of the member and fillet is at least one and one-half times the thickness of the member. No portion of a fillet shall be considered as adding to the effective depth. The effective span length of slabs shall be as specified in Article 3.24.1. 8.8.3

TABLE 8.9.2 Recommended Minimum Depths for Constant Depth Members Minimum Depth in Feei’~ Superstructure Type Simple Spans Continuous Spans Bridge stabs with main reinforcement parallel to traffic

t.2(S + tO)130

(S + tO)/30 =0.542

T-Girders

O.070S

0.065S

Box-Girders

O.060S

0.055S

Pedestrian Structure Girders

O.033S

0.0335

When variable depth members are used, vatues may be adjusted to account for change in relative smiffness of positive and negative moment sections. S = span length as defined in Articte 8.8 in feet.

8.9 CONTROL OF DEFLECTIONS 8.9.1

General

Flexural members of bridge structures shall be designed to have adequate stiffness to limit deflections or any deformations that may adversely affect the strength or serviceability of the structure at service load plus impact. 8.9.2

Superstructure Depth Limitations

thickness of the slab or one-half the clear distance to the

next web. 8.10.1.2 For girders having a slab on one side only, the effective overhanging flange width shall not exceed /2 of the span length of the girder, six times the thickness of the slab, or one-half the clear distance to the next web. 8.10.1.3

Isolated T-girders in which the T-shape is

used to provide a flange for additional compression area The minimum depths stipulated in Table 8.9.2 are recommended unless computation of deflection indicates that lesser depths may be used without adverse effects.

8.9.3

Superstructure Deflection Limitations

When making deflection computations, the following criteria are recommended.

8.9.3.1 Members having simple or continuous spans preferably should be designed so that the deflection due to service live load plus impact shall not exceed 1/800 of the span, except on bridges in urban areas used in part by pedestrians whereon the ratio preferably shall not exceed 1/1000. 8.9.3.2 The deflection of cantilever arms due to service live load plus impact preferably should be limited to 1/300 of the cantilever arm except for the case including pedestrian use, where the ratio preferably should be 1/375.

shall have a flange thickness not less than one-half the width of the girder web and an effective flange width not more than four times the width of the girder web. 8. 10.1.4 For integral bent caps, the effective flange width overhanging each side of the bent cap web shall not exceed six times the least slab thickness, or /~ the span

length of the bent cap. For cantilevered bent caps, the span length shall be taken as two times the length of the cantilever span.

8.10.2

Box Girders

8.10.2.1 The entire slab width shall be assumed effective for compression. 8.10.2.2

For integral bent caps. see Article 8.10. 1.4.

8.10 COMPRESSION FLANGE WIDTH

8.11

8.10.1

8.11.1 The thickness of deck slabs shall be designed in accordance with Article 3.24.3 but shall not be less than

T-Girder

SLAB AND WEB THICKNESS

8.10.1.1 The total width of slab effective as a Tgirder flange shall not exceed one-fourth of the span

specified in Article 8.9.

length of the girder. The effective flange width overhanging on each side of the web shall not exceed six times the

8.11.2

The thickness of the bottom slab of a box girder

shall be not less than V of the clear span between girder

8.11.2

DIVISION I—DESIGN

167

webs or S Y~ inches, except that the thickness need not be greater than the top slab unless required by design.

loading shall be considered uniformly distributed to all longitudinal flexural members.

8.11.3

8.13.3 Deflections that occur immediately on application of load shall be computed by the usual methods or formulas for elastic deflections. Unless stiffness values are obtained by a more comprehensive analysis, immediate deflections shall be computed taking the modulus of

When required by design, changes in girder web

thickness shall be tapered for a minimum distance of 12

times the difference in web thickness. 8.12

8.12.1

DIAPHRAGMS

elasticity for concrete as specified in Article 8.7 for nor-

Diaphragms shall be used at the ends of T-girder

and box girder spans unless other means are provided

to resist lateral forces and to maintain section geometry. Diaphragms may be omitted where tests or structural

mal weight or lightweight concrete and taking the moment of inertia as either the gross moment of inertia, 1~, or the effective moment of inertia, I, as follows:

Ie=CMSL

analysis show adequate strength.

In T-girder construction, one intermediate diaphragm is recommended at the point of maximum positive moment for spans in excess of 40 feet. 8.12.2

1~

I

~~~M~tKJ j Icr =1g (81)

where: —

f,I 5~y,

(8-2)

8.12.3 Straight box girder bridges and curved box girder bridges with an inside radius of 800 feet or greater do not require intermediate diaphragms. For curved box girder

and f, = modulus of rupture of concrete specified in Article 8.15.2.1.1.

bridges having an inside radius less than 800 feet, inter-

For continuous members, effective moment of inertia may be taken as the average of the values obtained from

mediate diaphragms are required unless shown otherwise by tests or structural analysis. For such curved box girders, a maximum diaphragm spacing of 40 feet is recommended to assist in resisting torsion.

8.13 8.13.1

Equation (8-1) for the critical positive and negative moment sections. For prismatic members, effective moment of inertia may be taken as the value obtained from Eq. (8-I) at midspan for simple or continuous spans, and as the value at the support for cantilevers.

COMPUTATION OF DEFLECTIONS Computed deflections shall be based on the

cross-sectional properties of the entire superstructure section excluding railings, curbs, sidewalks, or any element

not placed monolithically with the superstructure section before falsework removal.

8.13.4

Unless values are obtained by a more comprehensive analysis, the long-time deflection for both normal weight and lightweight concrete flexural members shall be the immediate deflection caused by the sustained load considered, computed in accordance with Article 8.13.3,

multiplied by one of the following factors: (a) the Where the immediate has beendeflection based on Tg~ multiplication factordeflection for the long-time

8.13.2 Live load deflection may be based on the assumption that the superstructure flexural members act together and have equal deflection. The live loading shall

shall be taken as 4. (b) Where the immediate deflection has been based on

the multiplication factor for the long-time deflection shall he taken as 3 1 .2(A/A~) 1.6. I,,

consist of all traffic lanes fully loaded, with reduction in load intensity allowed as specified in Article 3.12. The live

—

=

Part C DESIGN 8.14

GENERAL

allowable stresses as provided in SERVICE LOAD DEor, alternatively, with reference to load factors and

SIGN

8.14.1

Design Methods

8.14.1.1

The design of reinforced concrete members

shall be made either with reference to service loads and

strengths as provided in STRENGTH DESIGN.

8.14.1.2 All applicable provisions of this specification shall apply to both methods of design, except Articles

8.14.1.2

HIGHWAY BRIDGES

168

3.5 and 3.17 shall not apply for design by STRENGTH

nected elements. Design for horizontal shear shall be in accordance with the requirements of Article 8.15.5.5 or

DESIGN.

Article 8.16.6.5. 8.14.1.3 The strength and serviceability requirements of STRENGTH DESIGN may be assumed to be

8.14.3

satisfied for design by SERVICE LOAD DESIGN if the service load stresses are limited to the values given in Article 8.15.2.

8.14.3.1 The combined flexure and axial load strength of an arch ring shall be in accordance with the

8.14.2

Composite Flexural Members

8.14.2.1 Composite flexural members consist of precast and/or cast-in-place concrete elements constructed in separate placements but so interconnected that all elements respond to superimposed loads as a unit. When considered in design, shoring shall not be removed until the supported elements have developed the design properties

required to support all loads and limit deflections and cracking. 8.14.2.2 The entire composite member or portions thereof may be used in resisting the shear and moment. The individual elements shall be investigated for all critical stages of loading and shall be designed to support all loads introduced prior to the full development of the de-

sign strength of the composite member. Reinforcement shall be provided as necessary to prevent separation of the individual elements.

8.14.2.3

If the specified strength, unit weight. or other properties of the various elements are different, the

properties of the individual elements, or the most critical values, shall be used in design.

8.14.2.4 In calculating the fiexural strength ofacomposite member by strength design, no distinction shall be made between shored and unshored members. 8.14.2.5

Concrete Arches

provisions of Articles 8.16.4 and 8.16.5. Slenderness effects in the vertical plane of an arch ring, other than tied

arches with suspended roadway, may be evaluated by the approximate procedure of Article 8.16.5.2 with the unsupported length. fr,, taken as one-half the length of the arch ring, and the radius of gyration, r, taken about an axms perpendicular to the plane of the arch at the quarter point of the arch span. Values of the effective length factor. k, given in Table 8.14.3 may be used. In Equation (8-41), C,, shall be taken as 1.0 and ~ shall be taken as 0.85.

8.14.3.2 Slenderness effects between points of lateral support and between suspenders in the vertical plane of a tied arch with suspended roadway. shall be evaluated by a rational analysis taking into account the requirements of Article 8.16.5.1.1. 8.14.3.3 The shape of arch rings shall conform, as nearly as is practicable. to the equilibrium polygon for full dead load. 8.14.3.4 In arch ribs and barrels, the longitudinal reinforcement shall provide a ratio of reinforcement area to gross concrete area at least equal to 0.01, divided equally between the intrados and the extrados. The longitudinal reinforcement shall be enclosed by lateral ties in accordance with Article 8.18.2. In arch barrels, upper and lower

levels of transverse reinforcement shall be provided that are designed for transverse bending due to loads from

columns and spandrel walls and for shrinkage and temperature stresses.

When an entire member is assumed to resist

the vertical shear, the design shall be in accordance with the requirements of Article 8.15.5 or Article 8.16.6 as for a monolithically cast member of the same cross-sectional shape.

8.14.2.6 Shear reinforcement shall be fully anchored intd) the interconnected elements in accordance with Article 8.27. Extended and anchored shear reinforcement may be included as ties f’or horizontal shear. 8.14.2.7 The design shall provide for full transfer of horizontal shear f’orces at contact surfaces of intercon-

8.14.3.5 If transverse expansion joints are not provided in the deck slab, the effects of the combined action

c)f the arch rib, columns and deck slab shall be considered. Expansion joints shall be provided in spandrel walls. TABLE 8.14.3

Effective Length Factors, k

Risc-to-Span Ratio

3-Hinged Arch

2-Hinged Arch

Fixed Arch

0.1—0.2

1.16

t.04

0.70

0.2—0.3

t.13

1.10

0.70

0.3—0.4

1.16

t.i6

0.72

8. 14.3.6

DIVISION I—DESIGN

8.14.3.6 Walls exceeding 8 feet in height on filled spandrel arches shall be laterally supported by transverse diaphragms or counterforts with a slope greater than 45 degrees with the vertical to reduce transverse stresses in the arch barrel. The top of the arch barrel and interior faces of the spandrel walls shall be waterproofed and a drainage system provided for the fill. 8.15

within the support and having for its upper base the loaded area, and having side slopes of I vertical to 2 horizontal. When the loaded area is subjected to high-edge stresses

due to deflection or eccentric loading, the allowable bearing stress on the loaded area, including any increase due to the supporting surface being larger than the loaded area, shall be multiplied by a factor of 0.75.

8.15.2.2

SERVICE LOAD DESIGN METHOD

(ALLOWABLE STRESS DESIGN) 8.15.1

169

Reinforcement

The tensile stress in the reinforcement. f~. shall not exceed the following:

(;eneral Requirements

8.15.1.1 Service load stresses shall not exceed the values given in Article 8.15.2.

Grade 40 reinforcement Grade 60 reinforcement

20,000 psi 24.000 psi

In straight reinforcement, the range between the max-

8.15.1.2

Development and splices of reinfom’cement shall be as required in Articles 8.24 through 8.32. 8.15.2

Allowable Stresses

8.15.2.1

Concrete

8.15.3

Stresses in concrete shall not exceed the following:

8. 15.2.1.1

Extreme fiber stress in compression, f,

0.40f’

Extreme fiber stress in tension for plain concrete, f,

0.2 If,

Modulus of rupture. f,, from tests, or. if data are not available: 7.5 3 5 5

Flexure

8.15.3.1 For the investigation of stresses at service loads, the straight-line theory of stress and strain in flexore shall be used with the following assumptions.

Fled-are

Normal weight concrete “Sand-lightweight” concrete “All-lightweight” concrete

imum tensile stress and the minimnum stress caused by live load plus impact shall not exceed the value given in Article 8.16.8.3. Bends in primary reinforcement shall be avoided in regions of high-stress range.

fJ f,’

8.15.3.2 The strain in reinforcemnent and concrete is directly proportional to the distance from the neutral axis. except that for deep flexural members with overall depth 4A to ratios greater than 3K~ distribution for continuous spansshall andbe forspan simple spans. a nonlinear of strain

considered. 8.15.3.3 In reinforced concrete members, concrete resists no tension

8.15.3.4 8.15.2.1.2

Shear

For detailed summary of allowable shear stress v see Article 8.15.5.2.

8.15.2.1.3

Bearing Stress

The modular ratio, n

=

EYE,. may be taken

as the nearest whole number (but not less than 6). Except in calculations for deflections, the value of n for lightweight concrete shall be assumed to be the same as for

normal weight concrete of the same strength. 8.15.3.5

In doubly reinforced flexural members, an

The bearing stress, f5. on loaded area shall not exceed 0.3(1 f,’. When the supporting surface is wider on all sides than the loaded area, the allowable bearin&stress on the

effective modular ratio of 2EIE, shall be used to trans-

loaded area may be multiplied by \~ A2/AI. but not by

8.15.4

more than 2. When the supporting surface is sloped or stepped. A2 may be taken as the area of the lower base of the largest frustrum of the right pyramid or cone contained wholly

The combined fiexural and axial load capacity of compression members shall be taken as 35 percent d)f that

form the compression reinforcement for stress computations. The cd)mpressive stress in such reinforcement shall not be greater than the allowable tensile stress. Compression Members

HIGHWAY BRIDGES

170

computed in accordance with the provisions of Article 8.16.4. Slenderness effects shall he included according to the requirements of Article 8.16.5. The term P. in Equation (8-41) shall he replaced by 2.5 times the design axial load. In using the provisions of Articles 8.16.4 and 8.16.5, j shall be taken as 1.0. 8.15.5

8.15.5.1.1

taken as 0.95 Vij. A more detailed calculation of the allowable shear stress can he made using: v~

(Vd) =0.9

f.>l,l00p~

——

d

(8-59)

but V, shall not exceed 4 \/i7 bd. For single cell box culverts only, V, for slabs monolithic with walls need not be taken less than 3 \/7 bd, and V, for slabs simply supported need not be taken less than 2.5 \/‘i7 bd. The quantity VndIMn shall not be taken greater than 1.0 where M, is the factored moment occurring simultaneously with Vn at the section considered. For slabs of box culverts under less than 2 feet of fill, applicable provisions of Articles 3.24 and 6.4 should be used.

8.16.6.8

Special Provisions for Brackets and Corbels*

8.16.6.8.1 Provisions of Article 8.16.6.8 shall apply to brackets and corbels with a shear span-to-depth ratio a5/d not greater than unity, and subject to a horizontal tensile force N~, not larger than Vn. Distance d shall be measured at the face of support. 8.16.6.8.2 Depth at the outside edge of bearing area shall not be less than 0.5d.

8.16.6.8.3 The section at the face of the support shall be designed to resist simultaneously a shear V~, a moment (V~a, N~, (h d)), and a horizontal tensile force Na,. Distance h shall be measured at the face of support. ±

(a) Shear strength V~ shall be computed by Equation (8-47), where shear strength V, shall be in accordance

8.16.6.6.1

—

(a) In all design calculations in accordance with Article 8.16.6.8, the strength reduction factor 4) shall be taken equal to 0.85. (b) Design of shear-friction reinforcement A,f to resist shear V, shall be in accordance with Article 8.16.6.4. For normal weight concrete, shear strength V~ shall not be taken greater than 0.2f,’b~d nor 800b~d in pounds. For “all lightweight” or “sand-lightweight” concrete, shear strength V~ shall not be taken greater than (0.2 0.07a,/d)fb~d nor (800 280a~/d)b~d in pounds. (c) Reinforcement A, to resist moment (V~a. -tN~, (h d)) shall be computed in accordance with Articles 8.16.2 and 8.16.3. (d) Reinforcement A~ to resist tensile force Nn, shall be determined from N~, 4)A~f~. Tensile force N~, shall not be taken less than 0.2Vu unless special provisions are made to avoid tensile forces. Tensile force N~, —

—

=

8.16.6.7

Special Provisions for Slabs of Box Culverts

For slabs of box culverts under 2 feet or more fill, shear strength V, may be computed by: 8.16.6.7.l

*These provisions do not appty to beam tedges. The PCA pubtication, “Notes on ACt 31 8-83” contains an exatnpte design of beam tedges— Part t6, exampte t6-3.

DIVISION I—DESIGN

8.16.6.8.3

shall be regarded as a live load even when tension results from creep, shrinkage, or temperature change. (e) Area of primary tension reinforcement A, shall be made equal to the greater of (A~ An) or: ±

+A~. 3 8.16.6.8.4 Closed stirrups or ties parallel to A,, with a total area Ah not less than O.5(A, An), shall be uniformly distributed within two-thirds of the effective depth adjacent to A~. —

8.16.6.8.5 0.04(f7f 5).

Ratio p

=

A,/bd shall not be less than

8.16.6.8.6 At front face of bracket or corbel, primary tension reinforcement A, shall be anchored by one of the following:

(a) a structural weld to a transverse bar of at least equal size; weld to be designed to develop specified yield strength f,, of A, bars, (b) bending primary tension bars A, back to form a horizontal loop, or (c) some other means of positive anchorage.

8.16.7

Bearing Strength

8.16.7.1 The bearing stress, ~b, on concrete shall not exceed 0.854) f,’ except as provided in Articles 8.16.7.2, 8.16.7.3, and 8. 16.7.4. 8.16.7.2 When the supporting surface is wider on all sides than the loaded area, the allowable bearing stress on the loaded area may be multiplied by AlA,, but not by more than 2. 8.16.7.3 When the supporting surface is sloped or stepped, A2 may be taken as the area of the lower base of the largest frustum of a right pyramid or cone contained wholly within the support and having for its upper base the loaded area, and having side slopes of I vertical to 2 horizontal. 8.16.7.4 When the loaded area is subjected to high edge stresses due to deflection or eccentric loading, the allowable bearing stress on the loaded area, including

any increase due to the supporting surface being larger

than the loaded area, shall be multiplied by a factor of 0.75. 8.16.8

8.16.6.8.7 Bearing area of load on bracket or corbel shall not project beyond straight portion of primary tension bars A,, nor project beyond interior face of transverse anchor bar (if one is provided).

183

Serviceability Requirements

8.16.8.1

Application

For flexural members designed with reference to load factors and strengths by Strength Design Method, stresses at service load shall be limited to satisfy the requirements for fatigue in Article 8.16.8.3, and for distribution of reinforcement in Article 8.16.8.4. The requirements for control of deflections in Article 8.9 shall also be satisfied.

bearIng plate

-\

8.16.8.2 Service Load Stresses

I h

For investigation of stresses at service loads to satisfy the requirements of Articles 8.16.8.3 and 8.16.8.4, the straight-line theory of stress and strain in flexure shall be used and the assumptions given in Article 8.15.3 shall apply.

d

A~ (closed

8.16.8.3 Fatigue Stress Limits

stIrrups or tIes)

Frambig bar to anchor .i stIrrups or tIes

FIGURE 8.16.6.8

The range between a maximum tensile stress and minimum stress in straight reinforcement caused by live load plus impact at service load shall not exceed: f12l

0.33fnnn

±

8(r/h)

(8-60)

8. 16.8.3

HIGHWAY BRIDGES

184

where:

where: Zn

fnnn

Zn

r/h

=

A

stress range in kips per square inch;

=

algebraic minimum stress level, tension positive, compression negative in kips per square inch;

ratio of base radius to height of rolled-on transverse deformations; when the actual value is not known, use 0.3.

effective tension area, in square inches, of concrete surrounding the flexural tension reinforcement and having the same centroid as that reinforcement, divided by the number of bars or wires. When the flexural reinforcement consists

of several bar or wire sizes, the number of bars or wires shall be computed as the total area of reinforcement divided by the area of the largest bar or wire used. For calculation purposes, the thick-

Bends in primary reinforcement shall be avoided in regions of high stress range. Fatigue stress limits need not be considered for concrete deck slabs with primary reinforcement perpendicular to traffic and designed in accordance with the approximate methods given under Article 3.24.3. Case A.

ness of clear concrete cover used to compute A shall not be taken greater than 2 in. Zn

distance measured from extreme tension fiber to center of the closest bar or wire in inches. For calculation purposes, the thickness of clear concrete cover used to compute d, shall not be taken

8.16.8.4

greater than 2 inches.

Distribution of Flexural Reinforcement

To control flexural cracking of the concrete, tension reinforcement shall be well distributed within maximum flexural zones. When the design yield strength, f,, for tension reinforcement exceeds 40,000 psi, the bar sizes and spacing at maximum positive and negative moment sections shall be chosen so that the calculated stress in the reinforcement at service load f,, in ksi does not exceed the value computed by: z (8.61) (dcA)i/3 =0.6fy fZn

The quantity z in Equation (8-61) shall not exceed 170 kips per inch for members in moderate exposure conditions and 130 kips per inch for members in severe exposure conditions. Where members are exposed

to very aggressive exposure or corrosive environments, such as deicer chemicals, protection should be provided by increasing the denseness or imperviousness to water or furnishing other protection such as a waterproofing protecting system, in addition to satisfying Equation (8-61).

Part D REINFORCEMENT

8.17

is at least one-third greater than that required by analysis based on the loading combinations specified in Article

REINFORCEMENT OF FLEXURAL MEMBERS

3.22.

8.17.1

Minimum Reinforcement

8.17.1.1

At any section of a flexural member where

tension reinforcement is required by analysis, the reinforcement provided shall be adequate to develop a moment at least 1.2 times the cracking moment calculated on the basis of the modulus of rupture for normal weight concrete specified in Article 8.15.2.1.1. 4)Mu=1.2 M~r

(8-62)

8.17.1.2 The requirements of Article 8.17.1.1 may be waived if the area of reinforcement provided at a section

8.17.2

Distribution of Reinforcement

8.17.2.1

Flexural Tension Reinforcement in Zones of Maximum Tension

8.17.2.1.1 Where flanges of I-girders and box-girders are in tension, tension reinforcement shall be distributed over an effective tension flange width equal to V 5

the girder span length or a width as defined in Article 8. 10.1, whichever is smaller. If the actual slab width, center-to-center of girder webs, exceeds the effective tension

DIVISION I—DESIGN

8.17.2.1.1

flange width, and for excess portions of the deck slab overhang, additional longitudinal reinforcement with area not less than 0.4 percent of the excess slab area shall be provided in the excess portions of the slab.

8.17.2. 1.2

For integral bent caps of T-girder and boxgirder comistruetion, tension reinforcement shall be placed within a width not to exceed the web width plus an overhanging slab width on each side of the bent cap web equal to one-fourth the average spacing of the intersecting girder webs or a width as defined in Article 8.10.1.4 for integral bent caps, whichever is smaller.

185

tributed over both surfaces with a maximum spacing of 18 inches. All transverse reinforcement in the bottom slab shall

extend to the exterior face of the outside girder web in each group and be anchored by a standard 90-degree hook. 8.17.3

Lateral Reinforcement of Flexural Members

8.17.3.1

Compression reinforcement used to in-

crease the strength of flexural members shall be enclosed by ties or stirrups whieb shall be at least No.3 in size for

longitudinal bars that are No. 10 or stnaller, and at least No. 4 in size for No. 11, No. 14. No. 18. and bundled lon-

gitudinal bars. Welded wire fabric of equivalent area may 8.17.2.1.3

If the depth of the side face of a member exceeds 3 feet, longitudinal skin reinforcement shall be uniformly distributed along both side faces of the member tor a distance d/2 nearest the flexural tension reinforcement. The area of skin reinforcement ~ per foot of height on each side face shall be = 0.012 (d -— 30). The maximum spacing of skin reinforcement shall not exceed the lesser of d/6 and 12 inches ..Such reinforcement may be included in strength cotnputations if a strain compatibility analysis is made to determine stresses in the individual bars or wires. The total area of longitudinal skin reinforcement in both faces miced not exceed one-half of the required fiexural tensile reinfom’cement. 8.17.2.2

Transverse Deck Slab Reinforcement in T-Girders and Box Girders

At least one-third of the bottom layer of the transverse reinforcement in the deck slab shall extend to the exterior face of the outside girder web in each group and be anchored by a standard 90-degree hook. If the slab extends beyond the last girder web, such reinforcement shall extend into the slab overhang and shall have an anchorage beyond the exterior face of the girder web not less thati that provided by a standard hook.

be used instead of bars. The spacing of ties shall not exceed 16 longitudinal bar diameters. Such stirrups or ties shall be provided throughout the distance where the compression reinforcement is required. This paragraph does not apply to reinforeement located in a compression zone which has not been considered as compression reinforce-

ment in the design of the member. 8.17.3.2 Torsion reinforcement, where required, shall comisist of closed stirrups, closed ties, or spirals, coinbined with longitudinal bars. See Article 8.15.5.1.1 or 8.16.6.1.1. 8.17.3.3 Closed stirrups orties may be formed in one piece by overlapping the standard end hooks of ties or stirrups around a longitudinal bar, or may be formed in one or two pieces by splicing with Class C splices (lap of 1.7 f’d). 8.17.3.4

8.18 8.17.2.3

Bottom Slab Reinforcement for Box Girders

forcement may be provided. The spacing of such rein-

forcement shall not exceed 18 inches. 8.17.2.3.2

Minimum distributed reinforcement of 0.5

percent of the cross-sectional area of the slab, based on the least slab thickness, shall be placed in the bottom slab transverse to the girder span. Such reinforcement shall be dis-

REINFORCEMENT OF COMPRESSION

MEMBERS 8.18.1

8.17.2.3.1 Minimum distributed reinf’orcement of 0.4 percent of the flange area shall be placed in the bottom slab parallel to the girder span. A single layer of rein-

In seismic areas, where an earthquake that

could cause major damage to construction has a high probability of occurrence, lateral reinforcenient shall be designed and detailed to provide adequate strength and dnmctility to resist expected seismic movements.

Maximum and Minimum Longitudinal

Reinforcement 8.18.1.1 The area of longitudinal reimiforcement for compression members shall not exceed 0.08 timi~es the gross area. A,, of the section. 8.18.1.2 The minimum area of longitudimial reimiforcement shall not be less than 0.01 times the gross area, A,, of the section. When the cross section is larger than that required by consideration of loading, a reduced ef-

HIGHWAY BRIDGES

186

fective area may be used. The reduced effective area shall not be less than that which would require I percent of longitudinal reinforcement to carry the loading. The minimum number of longitudinal reinforcing bars shall be six for bars in a circular arrangement and four for bars in a rectangular arrangement. The minimum size of bars shall be No. 5. 8.18.2

Lateral Reinforcement

8.18.2.1

8.18.2.2.7 Spirals shall he of such size and so assembled to permit handling and placing without distortion from designed dimensions. 8.18.2.2.8 Spirals shall be held firmly in place by attachment to the longitudinal reinforcement and true to line by vertical spacers. 8.18.2.3

Spirals

Spiral reinforcement for compression members shall conform to the following: 8.18.2.2.1 Spirals shall consist of evenly spaced continuous bar or wire, with a minimum diameter of V~ inch. 8. 18.2.2.2 The ratio of spiral reinforcement to total volume of core, p~, shall not be less than the value given by:

8.18.2.3.1 All bars shall be enclosed by lateral ties which shall be at least No. 3 in size for longitudinal bars that are No. 10 or smaller, and at least No. 4 in size for No. II, No. 14, No. 18, and bundled longitudinal bars. Deformed wire or welded wire fabric of equivalent area may be used instead of bars. 8.18.2.3.2 The spacing of ties shall not exceed the least dimension of the compression member or 12 inches. When two or more bars larger than No. 10 are bundled together, tie spacing shall be one-half that specified above.

8.18.2.3.3 Ties shall be located not more than half a tie spacing from the face of a footing or from the nearest longitudinal reinforcement of a cross-framing member. 8.18.2.3.4

Zn

Ties

Tie reinforcement for compression members shall conform to the following:

General

In a compression member that has a larger cross seclion than that required by conditions of loading, the lateral reinforcement requirements may be waived where structural analysis or tests show adequate strength and feasibility of construction. 8.18.2.2

8.18. 1.2

o.4S(~k —1>

(8 63)

where f5 is the specified yield strength of spiral reinforcement but not more than 60,000 psi.

No longitudinal bar shall be more than 2

feet, measured along the tie, from a restrained bar on emther side. A restrained bar is one which has lateral support provided by the corner of a tie having an included angle of not more than 135 degrees. Where longitudinal bars are located around the perimeter of a circle, a complete circular tie may be used. 8.18.2.4

Seismic Requirements

8.18.2.2.3 The clear spacing between spirals shall not exceed 3 inches or be less than 1 inch or 1 V~ times the maximum size of coarse aggregate used.

cause major damage to construction has a high probabil-

8.18.2.2.4 Anchorage of spiral reinforcement shall be provided by 1 V2 extra turns of spiral bar or wire at each end of a spiral unit.

ity of occurrence, lateral reinforcement for column piers shall be designed and detailed to provide adequate strength and ductility to resist expected seismic movements.

8.18.2.2.5 Spirals shall extend from top of footing or other support to the level of the lowest horizontal reinforcement in members supported above. 8.18.2.2.6 Splices in spiral reinforcement shall be lap splices of 48 bar or wire diameters but not less than 12 inches, or shall be welded.

In seismic areas, where an earthquake which could

8.19 LIMITS FOR SHEAR REINFORCEMENT 8.19.1

Minimum Shear Reinforcement

8.19.1.1

A minimum area of shear reinforcement

shall be provided in all flexural members, except slabs and

footings, where:

187

DIVISION I—DESIGN

8. 19.1.1

(a) For design by Strength Design, factored shear force V~ exceeds one-half the shear strength provided by concrete 4V~

8.20 SHRINKAGE AND TEMPERATURE REINFORCEMENT

(b) For design by Service Load Design, design shear stress v exceeds one-half the permissible shear stress carried by concrete v,.

8.20.1 Reinforcement for shrinkage and temperature stresses shall be provided near exposed surfaces of walls and slabs not otherwise reinforced. The total area of reinforcement provided shall be at least Vu square inch per foot in each direction.

8.19.1.2 Where shear reinforcement is required by Article 8.19.1 .1, or by analysis, the area provided shall not be less than: SOb s

A

5Zn

~

(8-64)

where b~ and s are in inches. 8.19.1.3 Minimum shear reinforcement requirements may be waived if it is shown by test that the required ultimate flexural and shear capacity can be developed when shear reinforcement is omitted.

8.19.2

Types of Shear Reinforcement

8.19.2.1

8.20.2 The spacing of shrinkage and temperature reinforcement shall not exceed three times the wall or slab thickness, or 18 inches. 8.21

8.21.1 For cast-in-place concrete the clear distance between parallel bars in a layer shall not be less than 1.5 bar diameters, 1.5 times the maximum size of the coarse aggregate, or 1V2 inches. 8.21.2 For precast concrete (manufactured under plant control conditions) the clear distance between parallel bars in a layer shall be not less than I bar diameter, l/~ times the maximum size of the coarse aggregate, or 1 inch.

Shear reinforcement may consist of: 8.21.3

(a) Stirrups perpendicular to the axis of the member or making an angle of 45 degrees or more with the longitudinal tension reinforcement. (b) Welded wire fabric with wires located perpendic-

ular to the axis of the member. (c) Longitudinal reinforcement with a bent portion

making an angle of 30 degrees or more with the longitudinal tension reinforcement. (d) Combinations of stirrups and bent longitudinal reinforcement. (e) Spirals. 8.19.2.2 Shear reinforcement shall be developed at both ends in accordance with the requirements of Article 8.27. 8.19.3

SPACING LIMITS FOR REINFORCEMENT

Where positive or negative reinforcement is

placed in two or more layers, bars in the upper layers shall

be placed directly above those in the bottom layer with the clear distance between layers not less than 1 inch. 8.21.4 The clear distance limitation between bars shall also apply to the clear distance between a contact lap splice and adjacent splices or bars.

8.21.5 Groups of parallel reinforcing bars bundled in contact to act as a unit shall be limited to 4 in any one bundle. Bars larger than No. II shall be limited to two in any one bundle in beams. Bundled bars shall be located within stirrups or ties. Individual bars in a bundle cut off within the span of a member shall terminate at points at least 40-bar

diameters apart. Where spacing limitations are based on bar diameter, a unit of bundled bars shall be treated as a single bar of a diameter derived from the equivalent total area.

Spacing of Shear Reinforcement 8.21.6

Spacing of shear reinforcement placed perpendicular to the axis of the member shall not exceed d/2 or 24 inches. Inclined stirrups and bent longitudinal reinforcement shall be so spaced that every 45-degree line extending toward the reaction from the mid-depth of the member, d/2, to the longitudinal tension reinforcement shall be crossed by at least one line of shear reinforcement.

In walls and slabs the primary flexural reinforce-

ment shall be spaced not farther apart than 1.5 times the wall or slab thickness, or 18 inches. 8.22

PROTECTION AGAINST CORROSION

8.22.1 The following minimum concrete cover shall be provided for reinforcement:

)

HIGHWAY BRIDGES

188

Minimum Cover (inches Concrete cast against and permanently exposed to earth Concrete exposed to earth or weather: Primary reinforcement Stirrups, ties, and spirals

Concrete deck slabs in mild climates: Top reinforcement Bottom reinforcement Concrete deck slabs which have no positive corrosion protection and are frequently exposed to deicing salts: Top reinforcement Bottom reinforcement Concrete not exposed to weather or in contact with ground: Primary reinforcement Stirrups, ties, and spirals Concrete piles cast against andlor permanently exposed to earth

3

(hI No. 6, No. 7, and No. 8 bar, 90-deg bend plus I 2dh extension at free end of bar, or (c) No. 8 bar and smaller, 135-deg bend plus 6d 5

2

extension at free end of bar. 8.23.2

Minimum Bend Diameters

8.23.2.1 Diameter of bend measured on the inside of the bar, other than for stirrups and ties, shall not be less than the values given in Table 8.23.2.1.

I/

8.23.2.2 The inside diameter of bend for stirrups and ties shall not be less than 4 bar diameters for sizes No. 5

and smaller. For bars larger than size No. 5 diameter of 2

8.22.2 For bundled bars, the minimum concrete cover shall be equal to the equivalent diameterof the bundle, but need not be greater than 2 inches, except for concrete cast against and permanently exposed to earth in which case the minimum cover shall be 3 inches. 8.22.3

(I) 180-deg bend plus 4db extension, but not less than 2V2 in. at free end of bar. (2) 90-deg bend plus 12db extension at free end of bar. (3) For stirrup and tie hooks: (a) No. 5 bar and smaller, 90-deg bend plus 6d,, extension at free end of bar, or

2 I V2

2/2

8.22.1

In corrosive or marine environments or other se-

bend shall be in accordance with Table 8.23.2.1.

8.23.2.3

The inside diameter of bend in smooth or dc-

formed welded wire fabric for stirrups and ties shall not be less than 4-wire diameters for deformed wire larger than D6 and 2-wire diameters for all other wires. Bends with inside

diameters of less than 8-wire diameters shall not be less than 4-wire diameters from the nearest welded intersection.

vere exposure conditions, the amount of concrete protec-

tion shall he suitably increased, by increasing the denseness and imperviousness to water of the protecting

8.24 DEVELOPMENT OF FLEXURAL REINFORCEMENT

concrete or other means. Other means of positive corrostun protection may consist of, but not be limited to.

epoxy-coated bars, special concrete overlays, and impervious membranes; or a combination of these means.* 8.22.4 Exposed reinforcement, inserts, and plates intended for bonding with future extensions shall be protected from corrosion.

8.23 8.23.1

HOOKS AND BENDS Standard Hooks

The term “standard hook” as used herein shall mean one of the following:

*For additionat information on corrosion protection methods, refer to Nationat Cooperative Highway Research Report 297. ‘Evatuation of

Bridge Deck Protective Strategies.”

8.24.1

General

8.24.1.1 The calculated tension or compression in the reinforcement at each section shall he developed on each side of that section by embedment length. hook or mechanical device. or a combination thereof. Hooks may

be used in developing bars in tension only. 8.24.1.2 Critical sections for development of reinforcement in flexural members are at points of maximum

stress and at points within the span where adjacent rein-

forcemnent terminates or is bent. The provisions of Article 8.24.2.3 must also be satisfied. TABLE 8.23.2.1

Minimum Diameters of Bend

Bar Size

Minimum Diameter

Nos. 3 through 8

6-bar diameters

Nos. 9, 10, and 11 Nos. 14 and 18

8-bar diameters 10-bar diameters

8.24.1.2.

DIVISION I—DESIGN

8.24.1.2.1

Reinforcement shall extend beyond the

point at which it is no longer required to resist flexure for a distance equal to the effective depth of the member, 15 bar diameters, or V

2 of the clear span, whichever is

greater, except at supports of simple spans and at the free ends of cantilevers. 8.24./.2.2 Continuing reinforcement shall have an embedment length not less than the development length (d beyond the point where bent or terminated tension reinforcement is no longer required to resist flexure.

8.24.1.3

Tension reinforcement may be developed by

bending across the web in which it lies or by making it continuous with the reinforcement on the opposite face of the member.

8.24.1.4 Flexural reinforcement within the portion of the member used to calculate the shear strength shall not be terminated in a tension zone unless one of the following conditions is satisfied: 8.24.1.4.1 The shear at the cutoff point does not exceed two-thirds of that permitted, including the shear strength of shear reinforcement provided. 8.24. 1.4.2 Stirrup area in excess of that required for shear is provided along each terminated bar over a distance from the termination point equal to three-fourths the effective depth of the member. The excess stirrup area, A~, shall not be 13h) lesswhere than 13,60 Spacing, s, shall not ~ is bZs/fS. the ratio of the area of reinexceed dI(8cut off to the total area of tension reinforcement forcement at the section. 8.24.1.4.3 For No. II bars and smaller, the continuing bars provide double the area required for fiexure at the cutoff point and the shear does not exceed three-fourths that permitted. 8.24.1.5 Adequate end anchorage shall be provided l’or tension reimiforcement in fiexural members where reinforcement stress is not directly proportional to moment. such as: sloped, stepped, or tapered footings; brackets; deep fiexural members; or members in which the tension reinforcement is not parallel to the compression face. 8.24.2

Positive Moment Reinforcement

8.24.2.1 At least one-third the positive moment reinforcement in simple members and one-fourth the positive

189

8.24.2.2

When a fiexural member is part of the lateral

load resisting system, the positive moment reinforcement required to be extended into the support by Article 8.24.2.1 shall be anchored to develop the specified yield strength, f 5, in tension at the face of the support. 8.24.2.3 At simple supports and at points of inflection, positive moment tension reinforcement shall be limited to a diameter such that (., computed for f, by Article 8.25 satisfies Eq. (8-65); except Eq. (8-65) need not be satisfied for reinforcement terminating beyond center line of simple supports by a standard hook, or a mechanical anchorage at least equivalent to a standard hook. M d

— +

V

(8-65)

where M is the computed moment capacity assuming all positive moment tension reinforcement at the section to be fully stressed. V is the maximum shear force at the section. t, at a support shall be the embedment length beyond the center of the support. At a point of inflection, e. shall be limited to the effective depth of the member or 12 d5, whichever is greater. The value M/V in the development length limitation may be increased by 30 percent when the ends of the reinforcement are confined by a compressive reaction.

8.24.3

Negative Moment Reinforcement

8.24.3.1 Negative moment reinforcement in a continuous, restrained, or cantilever member, or in any member of a rigid frame, shall be anchored in or through the supporting member by embedment length, hooks, or mechanical anchorage. 8.24.3.2

Negative moment reinforcement shall have

an embedment length into the span as required by Article 8.24.1. 8.24.3.3 At least one-third of the total tension reinforcement provided for negative moment at the suppom’t shall have an embedment length beyond the point of inflection not less than the effective depth of the member. 1 2bar diameters or s. of the clear span, whichever is greater.

8.25

DEVELOPMENT OF DEFORMED BARS AND DEFORMED WIRE IN TENSION

moment reinforcement in continuous members shall extend along the same face of the member into the support. In beams, such reinforcement shall extend into the support at least 6 inches.

The development length, t~, in inches shall be computed as the product of the basic development length dcfined in Article 8.25.1 and the applicable modification fac-

190

tor or factors defined in Article 8.25.2 and 8.25.3, but shall be not less than that specified in Article 8.25.4.

8.25.1

8.25

HIGHWAY BRII)GES td

8.25.3

The basic development length, modified by the

appropriate factors of Article 8.2S.2, may be multiplied by

the following factors when: The basic development length shall be:

No. II bars and smaller

0.O4AbfY

8.25.3.1

Reinforcement being developed in the length under consideration is spaced laterally at least 6 inches on center with at least 3 inches clear cover measured in the direction of the spacing 0.8

8.25.3.2

Anchorage or development for reinforcement strength is not specifically required or reinforcement in flexural members is in excess of that required by analysis

finC

but not less than

0.0004d

5f5

No. 14 bars

0.08Sf~ finC

No. 18 bars

0.1 If~

(A. required)/(A, provided)

deformed wire

0.03d finc

8.25.3.3

The basic development length shall be multiplied by the following applicable factor or factors:

Reinforcement is enclosed within a spiral of not less than 1/4 inch in diameter and not more than 4 inch pitch 0.7S

8.25.2

8.25.2.1

Top reinforcement so placed that more than 12 inches of concrete is cast below the reinforcement

1.4

The development length, ~d. shall not be less than 12 inches except in the computation of lap splices by Article 8.32.3 and development of shear reinforcement by Article 8.27.

8.25.4

8.26

DEVELOPMENT OF DEFORMED BARS IN

COMPRESSION 8.25.2.2

Lightweight aggregate

concrete when f,, is

but not less than 1.0 When f,, is not specified

less than 8 inches.

specified

C

“all lightweight” concrete ........l .33 “sand lightweight” concrete 1 .18

Linear interpolation may be

cover less than 3d,, or clear

The basic development length shall be 0.02d,,f,,/ f,’

8.26.2.1

spacing between bars

0.0003d,,f5,

Anchorage or development for reinforcement strength is not specifically required, or reinforcement is in excess of that required by analysis (A, required)! (A. provided)

1.5 1.IS

The product obtained when cmmbining the factor for top reinforcement with the applicable factor for epoxy coated reinforcement need not be taken greater than 1 .7

fd,

8.26.2 The basic development length may be multiplied by applicable factors when:

Bars coated with epoxy with

less than 6d,, All other cases

8.26.1

but not less than

applied when partial sand replacement is used.

8.25.2.3

The development length,

in inches, for deformed bars in compression shall be computed as the product of the basic development length of Article 8.26.1 and applicable modification factors of 8.26.2, but (d shall not be

6.7 f’

8.26.2.2

Reinforcement is enclosed in a spiral of not less than 1/4 inch in diameter and not more than 4-inch pitch 0.75

8.27 8.27

DIVISION I—DESIGN DEVELOPMENT OF SHEAR REINFORCEMENT

8.27.1 Shear reinforcement shall extend at least to the centroid of the tension reinforcement, and shall be carried as close to the compression and tension surfaces of the member as cover requirements and the proximity of other reinforcement permit. Shear reinforcement shall be anchored at both ends for its design yield strength. For composite flexural members, all beam shear reinforcement shall be extended into the deck slab or otherwise shall be adequately anchored to assure full beam design shear capacity. 8.27.2 The ends of single leg, single U, or multiple UstirrLlps shall be anchored by one of the following means: 8.27.2.1 A standard hook plus an embedment of the stirrup leg length of at least 0.5 t~ between the mid-depth of the member d/2 and the point of tangency of the hook. td above or below 8.27.2.2 An embedment length of the mid-depth of the member on the compression side but not less than 24-bar or wire diameters or, for deformed bars or deformed wire, 12 inches.

8.27.2.3 Bending around the longitudinal reinforcement through at least 180 degrees. Hooking or bending stirrups around the longitudinal reinforcement shall be considered effective anchorage only when the stirrups make an angle of at least 45 degrees with the longitudinal reinforcement. 8.27.2.4 For each leg of welded smooth wire fabric forming single U-stirrups, either: 8.27.2.4.1 Two longitudinal wires at 2-inch spacing along the member at the top of the U.

wire at the tension face shall not be farther from the face than the portion of primary flexural reinforcement closest to the face. 8.27.3 Pairs of U-stirrups or ties so placed as to form a closed unit shall be considered properly spliced when the laps are 1.7 ed. 8.27.4 Between the anchored ends, each bend in the continuous portion of a single U- or multiple U-stirrup shall enclose a longitudinal bar. 8.27.5 Longitudinal bars bent to act as shear reinforcement, if extended into a region of tension, shall be continuous with the longitudinal reinforcement and, if extended into a region of compression, shall be anchored beyond the mid-depth, d12, as specified for development length in Article 8.25 for that part of the stress in the reinforcement required to satisfy Equation (8-8) or Equation (8-54). 8.28

8.27.2.5 For each end of a single-leg stirrup of welded smooth or welded deformed wire fabric, there shall be two longitudinal wires at a minimum spacing of 2 in. and with the inner wire at least the greater of d/4 or 2 in. from mid-depth of member d12. Outer longitudinal

DEVELOPMENT OF BUNDLED BARS

The development length of individual bars within a bundle, in tension or compression, shall be that for the individual bar, increased by 20 percent for a three-bar bundle, and 33 percent for a four-bar bundle.

8.29

DEVELOPMENT OF STANDARD HOOKS IN TENSION

8.29.1

Development length fdh in inches, for deformed bars in tension terminating in a standard hook (Article 8.23.1) shall be computed as the product of the basic development length fhb of Article 8.29.2 and the applicable modification factor or factors of Article 8.29.3. but tdl, shall not be less than 8db or 6 inches, whichever is greater. 8.29.2

8.27.2.4.2 One longitudinal wire located not more than d14 from the compression face and a second wire closer to the compression face and spaced at least 2 inches from the first wire. The second wire may be located on the stirrup leg beyond a bend or on a bend with an inside diameter of bend of not less than 8-wire diameters.

191

Basic development length fhb for a hooked bar with f., equal to 60,000 psi shall be l.200dJ

f:

8.29.3 Basic development length #hb shall be multiplied by applicable modification factor or factors for:

8.29.3.1

Bar yield strength: Bars with f~ other than 60.000 psi fj60.000

8.29.3.2

Concrete cover: For No. II bar and smaller, side cover (normal to plane of hook) not less than ~ in_

8.29.3.2

HIGHWAY BRIDGES

192

~dh

and for 90-deg hook, cover on bar extension beyond hook not less than 2 in 0.7 8.29.3.3

8.29.3.4

ties or stirrups required

Ties or stirrups: For No. 11 bar and smaller, hook enclosed vertically or horizontally within ties or stirnip-ties spaced along the full development 3dh, where db is length (dh not greater than diameter of hooked bar 0.8 Excess reinforcement: Where anchorage or development for f~ is not specifically required, reinforcement in excess of that required by analysis (A. required)/(A. provided)

8.29.3.5

Lightweight aggregate concrete

1.3

8.29.3.6

Epoxy-coated reinforcement hooked bars with epoxy coating 1.2

8.29.4 For bars being developed by a standard hook at discontinuous ends of members with both side cover and top (or bottom) cover over hook less than 2/2 in., hooked bar shall be enclosed within ties or stirrups spaced along the full development length tdl,, not greater than 3dh.

less 2112

Section AA

FIGURE 8.29.4 Hooked-Bar Tie Requirements where db is the diameter of the hooked bar. For this case, the factor of Article 8.29.3.3 shall not apply. 8.29.5 Hooks shall not be considered effective in developing bars in compression.

8.30

8.30.1

DEVELOPMENT OF WELDED WIRE FABRIC IN TENSION Deformed Wire Fabric

8.30.1.1 The development length, #d, in inches of welded deformed wire fabric measured from the point of critical section to the end of wire shall be computed as the product of the basic development length of Article 8.30.1.2 or 8.30.1.3 and the applicable modification fact()r or factors of Articles 8.25.2 and 8.25.3 but (d shall not be less than 8 inches except in computation of lap splices by Article 8.32.5 and development of shear reinforcement by Article 8.27. 8.30.1.2 The basic development length of welded deformed wire fabric, with at least one cross wire within the development length not less than 2 inches from the point of critical section, shall be: O.O3db (f~ — 20,000)/VT>

(8-66)

but not less than, #3 through #8

(8-67) 5.w

#9, #10 and #11 #14 and #18

FIGURE 8.29.1

Hooked-Bar I)etails for Development of Standard Hooks

\

c

8.30.1.3 The basic development length of welded (leformed wire fabric, with no cross wires within the development length, shall be determined as for deformed wire in accordance with Article 8.25. ~The 2t),OOO has units of p..~i.

DIVISION I—DESIGN

8.30.2 8.30.2

Smooth Wire Fabric

The yield strength of welded smooth wire fabric shall be considered developed by embedment of two cross wires with the closer cross wire not less than 2 inches from the point of critical section. However, development length ~ measured from the point of critical section to outermost cross wire shall not be less than:

0.27

A

f W

Y

Jf.

(8- 68)

mnodi tied by (A, required)/(A. provided) for reinforcement mn excess of that required by analysis and by factor of Article 8.25.2 for lightweight aggregate concrete, but t~ shall not be less than 6 inches except in computation of lap splices by Article 8.32.6.

8.31

MECHANICAL ANCHORAGE

193

8.32.1.4 The length, f,~, shall be the development length for the specified yield strength, f 5, as given in Article 8.25. 8.32.2

Welded Splices and Mechanical Connections

8.32.2.1 Welded splices or other mechanical connections may be used. Except as provided herein, all welding shall conform to the latest edition of the American Welding Society publication, ~~StructuralWelding Code Reinforcing Steel.” 8.32.2.2 A full-welded splice shall have bars butted and welded to develop in tension at least 125 percent of the specified yield strength of the bar. 8.32.2.3 A full-mechanical connection shall develop in tension or compression, as required, at least 125 percent of the specified yield strength of the bar.

8.31.1

Any mechanical device shown by tests to be capable of developing the strength of reinforcemnent without damage to concrete may be used as anchorage.

8.32.2.4 Welded splices and mechanical connections not meeting requirements of Articles 8.32.2.2 and 8.32.2.3 may be used in accordance with Article 8.32.3.4.

8.31.2 Development of reinforcement may consist of a combination of mechanical anchorage plus additional embedment length of reinforcement between point of maximum bar stress and the mechanical anchorage.

8.32.3

8.32

SPLICES OF REINFORCEMENT

Splices of reinforcement shall be made only as shown on the design drawings or as specified, or as authorized by the Engineer.

8.32.1

Lap Splices

8.32.1.1 Lap splices shall not be used for bars larger than No. II, except as provided in Articles 8.32.4.1 and 4.4.11.4.1. 8.32.1.2 Lap splices of bundled bars shall be based on the lap splice length required for individLmal bars within a bundle. The length of lap, as prescribed in Article 8.32.3 or 8.32.4 shall be increased 20 percent for a three-bar bundle and 33 percent for a four-bar bundle. Individual bar splices within the bundle shall not overlap. 8.32.1.3 Bars spliced by noncontact lap splices in tiexural members shall not be spaced transversely farther apart than Y~ the required length of lap or 6 inches.

Splices of Deformed Bars and Deformed Wire in Tension

8.32.3.1 The minirnuni length of lap for tension lap splices shall be as required for Class A, B, or C splice, but not less than 12 inches. Class A splice Class B splice Class C splice 8.32.3.2

1.0 (d 1.3 fd 1.7 ~

Lap splices of deformed bars and deformed

wire in tension shall conform to Table 8.32.3.2.

8.32.3.3 Welded splices or mechanical connections used where the area of reinforcement provided is less than twice that required by analysis shall meet the requirements of Article 8.32.2.2 or 8.32.2.3. TABLE 8.32.3.2

Tension Lap Splices Maximum Percenm of A~ Spliced within Required Lap Length

(A~ provided)/(A, required) Equal to orGreater than 2 Less than 2

50

75

100

Class A Class B

Class A Class C

Class B Class C

Ramio of area of reinforcement provided to area of reinforcement required by analysis at splice location.

194

8.32.3.4 Welded splices or mechanical connections used where the area of reinforcement provided is at least twice that required by analysis shall meet the following: 8.32.3.4.1 Splices shall be staggered at least 24 inches and in such manner as to develop at every section at least twice the calculated tensile force at that section but not less than 20,000 psi for the total area of reinforcement provided. 8.32.3.4.2 In computing tensile force developed at each section, spliced reinforcement may be rated at the specified splice strength. Unspliced reinforcement shall be rated at that fraction of f~ defined by the ratio of the shorter actual development length to f~ required to develop the specified yield strength f~.

8.32.3.5 Splices in tension tie members shall be made with a full-welded splice or a full-mechanical connection in accordance with Article 8.32.2.2 or 8.32.2.3. Splices in adjacent bars shall be staggered at least 30 inches. 8.32.4

8.32.3.4

HIGHWAY BRIDGES

Splices of Bars in Compression

8.32.4.1

held in concentric contact by a suitable device. Bar ends shall terminate in flat surfaces within I ‘/2 degrees of a right angle to the axis of the bars and shall be fitted within 3 degrees of full bearing after assembly. End-bearing splices shall be used only in members containing closed ties, closed stirrups, or spirals.

8.32.4.3

Welded Splices or Mechanical Connections

Welded splices or mechanical connections used in compression shall meet the requirements of Article

8.32.2.2 or 8.32.2.3. 8.32.5

Splices of Welded Deformed Wire Fabric in Tension

8.32.5.1 The minimum length of lap for lap splices of welded deformed wire fabric measured between the ends of each fabric sheet shall not be less than 1.7 fd or 8 inches, and the overlap measured between the outermost cross wires of each fabric sheet shall not be less than 2 inches.

Lap Splices in Compression

The minimum length of lap for compression lap splices shall be0.0005f~d

5 in inches, but not less than 12 inches. When the specified concrete strength, ~ is less than 3,000 psi, the length of lap shall be increased by one-third.

When bars of different size are lap spliced in compression, splice length shall be the larger of: development length of the larger bar, or splice length of smaller bar. Bar sizes No. 14 and No. 18 may be lap spliced to No. 11 and smaller bars.

In compression members where ties along the splice have an effective area not less than 0.OOlShs, the lap splice length may be multiplied by 0.83, but the lap length shall not be less than 12 inches. The effective area of the ties shall be the area of the legs perpendicular to dimension h.

In compression members when spirals are used for lateral restraint along the splice, the lap splice length may be multiplied by 0.75, but the lap length shall not be less than

8.32.5.2 Lap splices of welded deformed wire fabric, with no cross wires within the lap splice length, shall be determined as for deformed wire in accordance with Article 8.32.3.1. 8.32.6

Splices of Welded Smooth Wire Fabric in Tension

The minimum length of lap for lap splices of welded smooth wire fabric shall be in accordance with the following: 8.32.6.1 When the area of reinforcement provided is less than twice that required by analysis at the splice location, the length of overlap measured between the outermost cross wires of each fabric sheet shall not be less than one spacing of cross wires plus 2 inches or less than 1 .5 ed, or 6 inches.

12 inches.

8.32.4.2

End-Bearing Splices

In bars required for compression only, the compressive

stress may be transmitted by bearing of square cut ends

8.32.6.2 When the area of reinforcement provided is at least twice that required by analysis at the splice location, the length of overlap measured between the outermost cross wires of each fabric sheet shall not be less than 1.5 fd or 2 inches.

Section 9 PRESTRESSED CONCRETE Part A GENERAL REQUIREMENTS AND MATERIALS 9.1 9.1.1

APPLICATION

d

General =

= =

Asr

=

A,

=

b

=

ES e

= =

fc,r

area of non-prestressed tension reinforcement (Articles 9.7 and 9.19) area of compression reinforcement (Article

=

9.19)

=

=

area of prestressing steel (Article 9.17) steel area required to develop the compressive strength of the overhanging portions of the flange (Article 9.17) steel area required to develop the compressive strength of the web of a flanged section (Articles 9.17-9.19) area of web reinforcement (Article 9.20) width of flange of flanged member or width of

=

=

rectangular member =

=

CR.

=

CR.

=

D

=

distance from the extreme compressive fiber to the centroid of the non-prestressed tension reinforcement (Articles 9.7 and 9.17-9.19)

Notations

=

distance from extreme compressive fiber to centroid of the prestressing force, or to centroid of negative moment reinforcing for precast girder bridges made continuous

The specifications of this section are intended for design of prestressed concrete bridge members. Members designed as reinforced concrete, except for a percentage of tensile steel stressed to improve service behavior, shall conform to the applicable specifications of Section 8. Exceptionally long span or unusual structures require detailed consideration of effects which under this Section may have been assigned arbitrary values. 9.1.2

=

width of cross section at the contact surface being investigated for horizontal shear (Article 9.20). width of a web of a flanged member loss of prestress due to creep of concrete (Article 9.16) loss of prestress due to relaxation of prestressing steel (Article 9. 16) nominal diameter of prestressing steel (Articles 9.17 and 9.27)

=

195

loss of prestress due to elastic shortening (Article 9.16) base of Naperian logarithms (Article 9.16) average concrete compressive stress at the c.g. of the prestressing steel under full dead load (Article 9.16) average concrete stress at the c.g. of the prestressing steel at time of release (Article 9.16) compressive strength of concrete at 28 days compressive strength of concrete at time of initial prestress (Article 9.15) average splitting tensile strength of lightweight aggregate concrete, psi stress due to unfactored dead load, at extreme fiber of section where tensile stress is caused by externally applied loads (Article 9.20) compressive stress in concrete (after allowance for all prestress losses) at centroid of cross section resisting externally applied loads or at junction of web and flange when the centroid lies within the flange (In a composite member, f~. is resultant compressive stress at centroid of composite section, or at junction of web and flange when the centroid lies within the flange, due to both prestress and moments resisted by precast member acting alone.)(Article 9.20) compressive stress in concrete due to effective prestress forces only (after allowance for all prestress losses) at extreme fiber of section where tensile stress is caused by externally applied loads (Article 9.20)

l96

HIGHWAY BRIDGES =

=

=

=

=

=

=

guaranteed ultimate tensile strength of the prestressing steel. A~f~

SI-I

=

the tnodulus of rupture of concrete, as defined in Article 9.15.2.3 (Article 9.18)

s

=

longitudinal spacing of the web reinforcement

total prestress loss, excluding friction (Article 9.16) effective steel prestress after losses average stress in prestressing steel at ultimate

55

=

noncomposite section mnodulus for the ex-

load

5,

=

yield stress of prestressin~ steel (Article 9.15)

=

0.90 f~ for low-relaxation wire or strand

=

treme fiber of section where the tensile stress ms =

fiber of section where the tensile stress ms 9.18) =

K L

Md,.

M ,.,

p p* p P. Q

average thickness of the flange of a flanged

member (Articles 9.17 and 9.18) = =

v

=

steel stress at jacking end (Article 9.16) steel stress at any point x (Article 9.16) permissible horizontal shear stress (Article

9.20) =

0.85 f~ for stress-relieved wire or strand 0.85 f~ for Type I (smooth) high strength bar

overall depth of member (Article 9.20) I= moment of inertia about the centroid of the cross section (Article 9.20) = friction wobble coefficient per foot of prestressmng steel (Article 9.16) = length of prestressing steel element from jack end to point x (Article 9.16) = moment causing flexural cracking at section due to externally applied loads (Article 9.20) = cracking moment (Article 9.18) = co[nposite dead load moment at the section (Commentary to Article 9. 18) = non-composite dead load moment at the section (Article 9.18) = maximum factored moment at section due to externally applied loads (Article 9.20) = nominal muoment strength of a section = factored moment at section ~ 4M. (Articles 9.17 and 9.18) A~/bd, ratio of non-prestressed tension reinforcement (Articles 9.7 and 9.17-9.19) = A~Ibd, ratio of prestressing steel (Articles 9.17 and 9.19) = AI/bd, ratio of compression reinforcement (Article 9. 19) = factored tendon force = statical moment of cross-sectional area, above or below the level being investigated for shear, about the centroid (Article 9.20)

caused by externally applied loads (Article

9.18) composite section modulus for the extreme caused by externally applied loads (Article

0.80 f~ for Type II (deformed) high-strength bar h

loss of prestress due to concrete shrinkage (Article 9.16) (Article 9.20)

ultimate stress of prestressing steel (Articles 9.15 and 9.17) yield stress ol~ non-prestressed conventional reinforcement in tension (Articles 9.19 and 9.20) yield stress of non-prestressed conven-

tional reinforcement in compression (Article 9.19)

=

9.1.2

=

=

nominal shear strength provided by concrete (Article 9.20) nomninal shear strength provided by concrete when diagonal cracking results from combined shear and moment (Article 9.20) nominal shear strength provided by concrete

when diagonal cracking results from exces-

=

smve principal tensile stress in web (Article 9.20) shear force at section due to unfactored dead

load (Article 9.20) =

factored shear force at section due to externally applied loads occurring simultaneously

with M,,.,, (Article 9.20)

=

nominal horizontal shear strength (Article 9.20) vertical component of effective prestress force at section (Article 9.20) nominal shear strength provided by shear reinforcement (Article 9.20) factored shear force at section (Article 9.2t)) distance from centroidal axis of gross section,

=

neglecting reinforcement, to extreme tiber in tension (Article 9.20) friction curvature coefficient (Article 9.16)

=

=

=

p

=

=

y*

=

total angular change of prestressing steel profile in radians from jacking end to point x (Article 9.16) factor for concrete strength, as delined in Article 8.16.2.7 (Articles ~. 17-9.19) factor for type of prestressing steel (Article

9.17) = = =

0.28 for low-relaxation steel 0.40 for stress-relieved steel 0.55 for bars

DIVISION I—DESIGN

9.1.3 9.1.3

Definitions

The following terms are defined for general use. Specialized definitions appear in individual articles. Anchorage Device—The hardware assembly used for transferring a post-tensioning force from the tendon wires, strands or bars to the concrete. Anchorage Seating—Deformation of anchorage

197

Elastic Shortening of Concrete—Shortening of member caused by application of forces induced by prestress ing. End Anchorage—Length of reinforcement, or mechanical anchor, or hook, or combination thereof, beyond point of zero stress mn reinforcement. End Block—Enlargedend section of member designed to reduce anchorage stresses. Friction ~post-tensioning)—Surface resistance be-

or seating of tendons in anchorage device when prestressing force is transferred from jack to anchorage device. Anchorage Spacing—Center-to-center spacing of anchorage devices. Anchorage Zone—The portion of the structure in which the concentrated prestressing force is transferred from the anchorage device into the concrete (Local Zone), and then distributed more widely into the structure (General Zone) (Article 9.21.1).

tween tendon and duct in contact during stressing. General Zone—Region within which the concentrated

Basic Anchorage Device—Anchorage device meeting the restricted bearing stress and minimum plate stiffness requirements of Articles 9.21.7.2.2 through 9.21.7.2.4; no acceptance test ms required for Basic

pockets Jacking Force—Temporary force exerted by device

Anchorage Devices. Bonded Tendon—Prestressing tendon that is bonded to concrete either directly or through grouting. Coating—Material used to protect prestressing tendons against corrosion, to reduce friction between tendon and duct, or to debond prestressing tendons. Couplers (Couplings)—Means by which prestressing force is transmitted from one partial-length prestressing tendon to another. Crcep of Concrete—Time-dependent deformation of concrete under sustained load. Curvature Friction—Friction resulting from bends

prestressing force spreads out to a more linear stress distribution over the cross section of the member (Saint Venant Region) (Article 9.2 1.2.1) Grout Opening or Vent—Inlet, outlet, vent, or drain in post-tensioning duct for grout, water, or air Intermediate Anchorage—Anchorage not located at the end surface of a member or segment; usually in the form of embedded anchors, blisters, ribs.~, or recess

that introduces tension into prestressing tendons. Local Zone—The volume of concrete surrounding and immediately ahead of the anchorage device, subjected to

high local bearing stresses (Article 9.21.2.2) Los.s of Prestres.s—Reduction in prestressing force resulting from combined effects of strains in concrete and steel, including effects of elastic shortening, creep and shrinkage of concrete, relaxation of steel stress, and for post-tensioned mnembers, friction and anchorage seating. Post-Tensioning—Method of prestressing in which tendons are tensioned after concrete has hardened. Precompressed Zone—Portion of flexural member

weight of member; stress remaining in prestressing tendons after all losses have occurred excluding effects of

cross seetmon compressed by prestressing force. Prestressed Concrete—Reinforced concrete in which internal stresses have been introduced to reduce potential tensile stresses mn concrete resulting from loads. Prerensioning—Method of prestressing in which tendons are tensioned before concrete is placed. Relaxation of Tendon Stress—Time-dependent reduction of stress in prestressing tendon at constant strain. Shear Lag—Nonuniform distribution of bending stress over the cross seetmon. Shrinkage of Concrete—Time-dependent deformation of concrete caused by drying and chemical changes (hydration process). Special Anchorage Device—Anchorage device whose adequacy must be proven experimentally in the standardized acceptance tests of Division II, Sectiorm

dead load and superimposed load.

10.3.2.3.

or curves in the specified prestressing tendon profile. Debonding (hlanketing)—Wrapping, sheathing, or coating prestressing strand to prevemit bond between

strand and surrounding concrete. Diaphragm—Transverse stiffener in girders to mamntam section geometry. Duct—Hole or void formed in prestressed member to accommodate tendon for post-tensioning. Edge Distance—Distance from the center of the

anchorage member.

device to

the

edge of

the concrete

Effective Prestress—Stress remaining in concrete due to prestressing after all calculated losses have been deducted, excluding effects of superimposed loads and

198

HIGHWAY BRIDGES

Tendon—Wire, strand, or bar, or bundle of such elements, used to impart prestress to concrete. Transfer—Act of transferring stress in prestressing tendons from jacks or pretensioning bed to concrete member. Transfer Length—Length over which prestressing force is transferred to concrete by bond in pretensioned members. Wobble Friction—Friction caused by unintended devmation of prestressing sheath or duct from its specified profile or alignment. Wrapping or Sheathing—Enclosure around a prestressing tendon to avoid temporary or permanent bond between prestressing tendon and surrounding concrete.

9.2

CONCRETE

The specified compressive strength, f~, of the concrete for each part of the structure shall be shown on the plans. The requirements for f~ shall be based on tests of cylinders made and tested in accordance with Division II, Section 8, ~‘ConcreteStructures.”

9.3 9.3.1

9.1.3

REINFORCEMENT Prestressing Steel

Wire, strands, or bars shall conform to one of the following specifications. “Uncoated Stress-Relieved Wire for Prestressed Concrete,” AASHTO M 204. “Uncoated Seven-Wire Stress-Relieved Strand for Prestressed Concrete,” AASHTO M 203. “Uncoated High-Strength Steel Bar for Prestressing Concrete,” ASTM A 722. Wire, strands, and bars not specifically listed in AASHTO M 204, AASHTO M 203, or ASTM A 722 may be used provided they conform to the minimum requirements of these specifications. 9.3.2

Non-Prestressed Reinforcement

Non-prestressed reinforcement shall conform to the requirements in Article 8.3.

Part B ANALYSIS 9.4 GENERAL

9.6

Members shall be proportioned for adequate strength usmng these specifications as minimum guidelines. Continuous beams and other statically indeterminate structures shall be designed for adequate strength and satisfactory behavior. Behavior shall be determined by elastmc analysis, taking into account the reactions, moments. shear, and axial forces produced by prestressing, the effects of temperature, creep, shrinkage, axial deformation, restraint of attached structural elements, and foundation settlement.

The effective span lengths of simply supported beams shall not exceed the clear span plus the depth of the beam. The span length of continuous or restrained floor slabs and beams shall be the clear distance between faces of support. Where fillets making an angle of 45 degrees or more with the axis of a continuous or restrained slab are built monolithic with the slab and support, the span shall be measured from the section where the combined depth of the slab and the fillet is at least one and one-half times the

9.5

EXPANSION AND CONTRACTION

SPAN LENGTH

thickness of the slab. Maximum negative moments are to

be considered as existing at the ends of the span, as above defined. No portion of the fillet shall be considered as adding to the effective depth.

9.5.1 In all bridges, provisions shall be made in the design to resist thermal stresses induced, or means shall be provided for movement caused by temperature

9.7

changes.

9.7.1

9.5.2

The effect of secondary moments due to prestressing shall be included in stress calculations at working load. In calculating ultimate strength moment and shear requirements, the secondary moments or shears induced by pre-

Movements not otherwise provided for, including

shortening during stressing, shall be provided for by means of hinged columns, rockers, sliding plates~, elastomeric pads, or other devices.

FRAMES AND CONTINUOUS CONSTRUCTION Cast-in-Place Post-Tensioned Bridges

9.7.1

DIVISION I—DESIGN

199

stressing (with a load factor of 1.0) shall be added alge-

segment weights and erection loads shall be accommo-

braically to the moments and shears due to factored or ultimate dead and live loads.

dated in pier design or with auxiliary struts. Erection equipment which can eliminate these unbalanced mo-

9.7.2

Bridges Composed of Simple-Span Precast Prestressed Girders Made Continuous

9.7.2.1

General

When structural continuity is assumed in calculating live loads plus impact and composite dead load moments, the effects of creep and shrinkage shall be considered in

the design of bridges incorporating simple span precast, prestressed girders and deck slabs continuous over two or more spans.

9.7.2.2

Positive Moment Connection at Piers

9.7.2.2.1 Provision shall be made in the design for the positive moments that may develop in the negative moment region due to the combined effects of creep and shrinkage in the girders and deck slab, and due to the effects of live load plus impact in remote spans. Shrinkage and elastic shortening of the pier shall be considered when significant.

Non-prestressed positive moment connection reinforcement at piers may be designed at a working stress of 0.6 times the yield strength but not to exceed 36 ksi. 9.7.2.2.2

9.7.2.3

Negative Moments

ments may be used. 9.7.3.2

Flexure

The transverse design of segmental box girders for

flexure shall consider the segments as rigid box frames. Top slabs shall be analyzed as variable depth sections considering the fillets between top slab and webs. Wheel loads shall be positioned to provide maximum moments, and elastic analysis shall be used to determine the effective longitudinal distribution of wheel loads for each load location. (See Article 3.11.) Transverse prestressing of top slabs is generally recommended. 9.7.3.3

Torsion

In the design of the cross section, consideration shall

be given to the increase in web shear resulting from eccentric loading or geometry of structure. 9.8 EFFECTIVE FLANGE WIDTH 9.8.1

T-Beams

9.8.1.1 For composite prestressed construction where slabs or flanges are assumed to act integrally with the beam, the effective flange width shall conform to the

9.7.2.3.1 Negative moment reinforcement shall be proportioned by strength design with load factors in ac-

provisions for T-girder flanges in Article 8.10. I.

cordance with Article 9.14.

9.8.1.2 For monolithic prestressed construction, with normal slab span and girder spacing, the effective flange width shall be the distance center-to-center of beams. For very short spans, or where girder spacing is excessmve, analytical investigations shall be made to determine the anticipated width of flange acting with the beam.

9.7.2.3.2 The ultimate negative resisting moment shall be calculated using the compressive strength of the girder concrete regardless of the strength of the diaphragm concrete. 9.7.3

Segmental Box Girders

9.7.3.1

General

9.7.3.1.1 Elastic analysis and beam theory may be used in the design of segmental box girder structures. 9.7.3.1.2 In the analysis of precast segmental box girder bridges, no tension shall be permitted across any joint between segments during any stage of erection or service loading. 9.7.3.1.3 In addition to the usual substructure design considerations, unbalanced cantilever moments due to

9.8.1.3

For monolithic prestressed design of isolated

beams, the flange width shall not exceed 15 times the web

width and shall be adequate for all design loads. 9.8.2

Box Girders

9.8.2.1 For cast-in-place box girders with normal slab span and girder spacing, where the slabs are considered an integral part of the girder, the entire slab width shall be assumed to be effective in compression.

9.8.2.2

For box girders of unusual proportions, in-

cluding segmental box girders, methods of analysis which

200

HIGHWAY BRIDGES

consider shear lag shall be used to determine stresses in

9.10

9.8.2.2

DIAPHRAGMS

the cross section due to longitudinal bending.

9.10.1 9.8.2.3 Adequate fillets shall be provided at the intersections of all surfaces within the cell of a box girder, except at the junction of web and bottom flange where none are required.

General

Diaphragms shall be provided in accordance with Articles 9.10.2 and 9.10.3 except that diaphragms may be omitted where tests or structural analysis show adequate strength.

9.8.3

Precast/Prestressed Concrete Beams with Wide Top Flanges

9.10.2

T-Beams

9.8.3.1 For composite prestressed concrete where slabs or flanges are assumed to act integrally with the precast beam, the effective web width of the precast beam

Diaphragms or other means shall be used at span ends to strengthen the free edge of the slab and to transmit lateral forces to the substructure. Intermediate diaphragms

shall be the lesser of (I) six times the maximum thickness of the flange (excluding fillets) on either side of the web plus the web and fillets, and (2) the total width of the top flange.

shall be placed between the beams at the points of maxi-

9.8.3.2 The effective flange width of the composite section shall be the lesser of (I) one-fourth of the span length of the girder, (2) six (6) times the thickness of the slab on each side of the effective web width as determined by Article 9.8.3. 1 plus the effective web width, and (3) one-half the clear distance on each side of the effective web width plus the effective web width.

9.10.3.1 For spread box beams, diaphragms shall be placed within the box and between boxes at span ends and at the points of maximum moment for spans over

9.9

FLANGE AND WEB THICKNESS—BOX GIRDERS

9.9.1

Top Flange

The minimum top flange thickness shall be Y~th of the clear distance between fillets or webs but not less than 6 inches, except the minimum thickness may be reduced for

factory produced precast. pretensioned elements to 5/2

inches.

9.9.2

Bottom Flange

The minimum bottom flange thickness shall be /rh of the clear distance between fillets or webs but not less than

tnum moment for spans over 40 feet.

9.10.3

Box Girders

80 feet. 9.10.3.2 For precast box multi-beam bridges, diaphragms are required only if necessary for slab-end

support or to contain or resist transverse tension ties. 9.10.3.3 For cast-in-place box girders, diaphragms or other means shall be used at span ends to resist lateral forces and maintain section geometry. Intermediate diaphragms are not required for bridges with inside radius of curvature of 800 feet or greater. 9.10.3.4 For segmental box girders. diaphragms shall be placed within the box at span ends. Intermediate diaphragms are not required for bridges with inside radius of curvature of 800 feet or greater.

9.10.3.5 For all types of prestressed boxes in bridges with inside radius of curvature less than 800 feet, intermediate diaphragms may be required and the spacing and strength of diaphragms shall be given special consideration in the design of the structure.

5% inches. except the minimum thickness may be reduced tor factory produced precast. pretensioned elements to 5 inches.

9.11

9.9.3

9.11.1

Web

Changes in girder stem thickness shall be tapered for a minimum distance of 12 times the difference in web thickness.

DEFLECTIONS General

Deflection calculations shall consider dead load, live load. prestressing. erection loads, concrete creep and

shrinkage, and steel relaxation.

9.11.2

9.11.2

Segmental Box Girders

9.12

Deflections shall be calculated prior to casting of segments and they shall be based on the anticipated casting and erection schedules. Calculated deflections shall be used as a guide against which actual deflection measurements are checked.

9.11.3

201

DIVISION I—DESIGN

9.12.1

DECK PANELS General

9.12.1.1 Precast prestressed deck panels used as permanent forms spanning between stringers may be designed compositely with the cast-in-place portion of the slabs to support additional dead loads and live loads.

Superstructure Deflection Limitations

When making deflection computations, the following criteria are recommended.

9.11.3.1 Memnbers having simple or continuous spans preferably should be designed so that the deflection due to service live load plus impact shall not exceed ‘/~ of the span, except on bridges in urban areas used in part by pedestrians whereon the ratio preferably shall not exceed i~. 9.11.3.2 The deflection of cantilever arms due to servmce live load plus impact preferably should be limited to 1/300 of the cantilever arm except for the case including pedestrian use, where the ratio preferably should be

9.12.1.2 The panels shall be analyzed assuming they support their self-weight, any construction loads, and the weight of the cast-in-place concrete, and shall be analyzed assuming they act compositely with the cast-in-place concrete to support moments due to additional dead loads amid live loads. 9.12.2

Bending Moment

9.12.2.1 Live load moments shall be computed in accordance with Article 3.24.3. 9.12.2.2 In caletmlating stresses in the deck panel due to negative moment near the stringer, no compression due to prestressing shall be assumed to extst.

Part C DESIGN 9.13 9.13.1

GENERAL Design Theory and General Considerations

9.13.1.1 Members shall meet the strength requirements specified herein. 9.13.1.2 Design shall be based on strength (Load Factor Design) and on behavior at service conditions (Allowable Stress Design) at all load stages that may be critmeal during the life of the structure from the time prestressing is first applied. 9.13.1.3 Stress concentrations due to the prestressing shall be considered in the design. 9.13.1.4 The effects of temperature and shrinkage shall be considered. 9.13.2

9.13.2.2 Before cracking. stress is linearly proportional to strain.

Basic Assumptions

The following assumptions are made for design purposes for monolithic members. 9.13.2.1 Strains vary linearly over the depth of the member throughout the entire load range.

9.13.2.3 glected. 9.13.3

After cracking, tension in the concrete ms ne-

Composite Flexural Members

Composite flexural members consisting of precast andlor cast-in-place concrete elements constn.tcted in separate placements but so interconnected that all elements respond to superimposed loads as a unit shall conform to the provisions of Articles 8.14.2.1 through 8.14.2.4, 8.14.2.6. and the following.

9.13.3.1 Where an entire member is assumed to resist the vertical shear, the design shall be in accordance with the requirements of Articles Q20.1 through 9.20.3. 9.13.3.2 The design shall provide for full transfer of horizontal shear forces at contact surfaces of interconnected elements. Design for horizontal shear shall be in accordance with the requirements of Article 9.20.4.

9.13.3.3 In structures with a cast-in-place slab on precast beams, the differential shrinkage tends to cause tensile stresses in the slab and in the bottom of the beams. Because the tensile shrinkage develops over an extended time period, the effect on the beams is reduced by creep. Differential shrinkage may influence the cracking load and the beam deflection profile. When these factors are particularly significant, the effect of differential shrinkage should be added to the effect of loads. 9.14

LOAD FACTORS

For factory produced precast prestressed concrete members 4) = 1.0 For post-tensioned cast-in-place concrete members 4) 0.95 For shear 4) = 0.90 For anchorage zones 4) 0.85 for normal weight concrete and 4) = 0.70 for lightweight concrete. —

ALLOWABLE STRESSES

The design of precast prestressed members ordinarily shall be based on f,~ = 5,000 psi. An increase to 6,000 psi is permissible where, in the Engineer’s judgment, it is reasonable to expect that this strength will be obtained consistently. Still higher concrete strengths may be consmdered on an individual area basis. In such cases, the Engineer shall satisfy himself completely that the controls over materials and fabrication procedures will provide the required strengths. The provisions of this Section are equally applicable to prestressed concrete structures and components designed with lower concrete strengths. 9.15.1

Prestressing Steel

Pretensioned members: Stress immediately prior to transfer-Low-relaxation strands Stress-relieved strands Post-tensioned members: Stress immediately after seating-At anchorage

At the end of the seating loss zone 0.83 f~ Tensioning to 0.90 f~ for short periods of time prior to seating may be permitted to offset seating and friction losses provided the stress at the anchorage does not exceed the above value. Stress at service loadt after losses 0.80 f~ 9.15.2

Concrete

9.15.2.1

The computed strength capacity shall not be less than the largest value from load factor design in Article 3.22. For the design of post-tensioned anchorage zones a load factorof 1.2 shall be applied to the maximum tendon jacking force. The following strength capacity reduction factors shall be used:

9.15

9.13.3.3

HIGHWAY BRIDGES

202

0.75 f~ 0.70 f~

0.70 f~

Temporary Stresses Before Losses Due to Creep and Shrinkage

Compression: Pretensioned members 0.60 f~, Post-tensioned members 0.55 f~, Tension: Precompressed tensile zone No temporary allowable stresses are specified. See Article 9.15.2.2 for allowable stresses after losses. Other Areas In tension areas with no bonded reinforcement 200 psi or 3 f~ Where the calculated tensile stress exceeds this value, bonded reinforcement shall be provided to resist the total tension force in the concrete computed on the assumption of an uncracked section. The maximum tensile stress shall not exceed 7.5 f,~, 9.15.2.2

Stress at Service Load After Losses Have Occurred

Compression:

(a) The compressive stresses under all load combinations, except as stated in (b) and (c), shall not exceed 0.60f~. (b) The compressive stresses due to effective prestress plus permanent (dead) loads shall not exceed 0.40f,~. (c) The compressive stress due to live loads plus onehalf of the sum of compressmve stresses due to prestress and permanent (dead) loads shall not exceed 0.40ff. Tension in the precompressed tensile zone: (a) For members with bonded reinforcement* 6 f~ For severe corrosive exposure conditions, such as coastal areas 3 f~ includes bonded prestressed sirands. tScrviee load consists of alt toads contained in Article include overload provisions.

~.

2 but does not

203

DIVISION I—DESIGN

9. 15.2.2 (b) For members without bonded reinforce-

tions. Rigid ducts shall have sufficient strength to main-

ment

tam their correct alignment without visible wobble during

0 limited by allowable temporary

Tension in other areas is stresses specified in Article 9.15.2.1.

9.15.2.3

placement of concrete. Rigid ducts may be fabricated with either welded or interlocked seams. Galvanizing of the welded seam will not be required.

Cracking Stress* 9.16.2

Modulus of rupture from tests or if not available. For normal weight concrete 7.5 For sand-lightweight concrete 6.3

f~ f~

For all other lightweight concrete

f~

9.15.2.4

5.5

Prestress Losses

9.16.2.1

General

Loss of prestress due to all causes, excluding friction,

may be determined by the following method.* The method is based on normal weight concrete and one of the following types of prestressing steel: 250 or flO ksi

Anchorage Bearing Stress

Post-tensioned anchorage at service load

. .

.3,000 psi

seven-wtre. stress-relieved or low-relaxation strand 240

9.16 LOSS OF PRESTRESS

ksi stress-relieved wires; or 145 to 160 ksi smooth or deformed bars. Refer to documented tests for data regarding the properties and the effects of lightweight aggregate concrete on prestress losses.

9.16.1

TOTAL LOSS

(but not to exceed 0.9 f.’,)

Friction Losses

Friction losses in post-tensioned steel shall be based on experimentally determined wobble and curvature coefficients, and shall be verified during stressing operattons. The values of coefficients assumed for design, and the acceptable ranges of jacking forces and steel elongations shall be shown on the plans. These friction losses shall be calculated as follows: =

T

e(KI

T~ (I

+

KL

Af,

=

The following values for K and p may be used when

+

ES

+

CR~

+

CR,

(9-3)

total loss excluding friction in pounds per square inch;

SH

=

ES

=

CR.

=

CR,

=

(9-2)

+ pci)

SH

where:

(9-I)

±

When (KL ± pz) is not greater than 0.3, the following equation may be used: =

=

loss due to concrete shrinkage in pounds per square inch; loss due to elastic shortening in pounds per square inch; loss due to creep of concrete in poitnds per square inch; loss due to relaxation of prestressing steel in

pounds per square inch

experimental data for the materials used are not available: 9.16.2.1.1 Type of Steel Wire or ungalvanized strand

High-strength bars

Type of Duct

K/ft

~j

Bright metal sheathing Galvanized metal sheathing Greased or asphalt-coated and wrapped Galvanized rigid Bright metal sheathing Galvanized metal sheathing

0.0020

0.30

0.0015

0.25

0.0020 0.0002 0.0003

0.30 0.25 0.20

0.0002

0.15

Friction losses occur prior to anchoring but should be estimated for design and checked during stressing opera5RcIer to Article 9.18.

Shrinkage

Pretensioned Members:

SH

=

17,000

—

150 RH

(9-4)

Post-tensioned Members: SH

=

0.80(17,000

—

150 RH)

(9-5)

~Should more exact prcstress losses hc desired, data represcnting the materials to bc used, thc methods of coring. thc ambient service condition and any pertincnt stmctural dctails should he determined for use in accordance with a method of calculating prestress losses that is supported by appropriate research data. See also FHWA Report FHWA/Rt) 85/t)45. Criteria for Designing Lighrweitht Concrete Bridi,’es.

9.16.2.1.1

HIGHWAY BRIDGES

204

where RH = mean annual ambient relative humidity in percent. (See Figure 9.16.2.1 .1.) 9.16.2.1.2

9.16.2.1.3

Creep of Concrete

Pretensioned and post-tensioned members:

Elastic Shortening

Pretensioned Members:

=

F5

fc,r

(9-6)

concrete stress at the center of gravity of the prestressing steel due to all dead loads except the dead load present at the time the prestressing force is applied.

Post-tensioned Members*: ES

=

where: =

ES

9.16.2.1.4

E =

(9-7)

Relaxation of Prestressing Steel*

Pretensioned Members: 250 to 270 ksi Strand CR, = 20,000 — 0.4 ES

where: =

=

(9-9)

12~cir~7~cds

CR5

modulus of elasticity of prestressing steel strand, which can be assumed to be 28 X l0~ psi; modulus of elasticity of concrete in psi at transfer of stress, which can be calculated from:

—

0.2 (SH + CR)

(9-10)

for stress relieved strand CR, = 5,000 0.10 ES 0.05 (SH for low relaxation strand —

—

-~

CR.) (9-bA)

Post-tensioned Members: 250 to 270 ksi Strand

E

312 f’.CI

(9-8)

51=33w

fnr

=

in which w is the concrete unit weight in pounds per cubic foot and f, is in pounds per square inch; concrete stress at the center of gravity of the prestressing steel due to prestressing force and dead load of beam immediately after transfer; fc,r shall be computed at the section or sections of maximum moment. (At this stage, the initial stress in the tendon has been reduced by elastic shortening of the concrete and tendon relaxation during placing and curing the concrete for pretensioned members, or by elastic shortening of the concrete and tendon friction for post-tensioned members. The reductions to initial tendon stress due to these factors can be estimated, or the reduced tendon stress can be taken as 0.63 f~ for stress relieved strand or 0.69 f~ for low relaxation strand in typical pretensioned members.)

*Certain tensioning procedures may alter the elastic shortening losses.

CR, = 20,000 0.3 FR 0.4 ES for stress relieved strand —

—

CR, = 5,000 0.07 FR 0.1 ES for low relaxation strand —

—

—

0.2 (SH + CR)

(9-Il) —

0.05 (SH ~ CR)

(9-Il A)

240 ksi Wire

CR,

=

18,000—0.3 FR —0.4 ES —0.2 (SH

+

CR)

(9-12)

145- to 160-ksi Bars CR, = 3,000 where: FR

=

ES, SH,

=

and CR.

friction loss stress reduction in psi below the level of 0.70 f~ at the point under consideration, computed according to Article 9.16.1. appropriate values as determined for either pre-tensioned or post-tensioned

members.

5The relaxation losses are based on alt initial stress eqoal to the stress at anchorages allowed by Article 9.15.1.

9.16.2.1.4

DIVISION I—DESIGN

205

= 5..

5..

‘C

HIGHWAY BRIDGES

206 9.16.2.2

Estimated Losses

satisfy Eq. (9-24), the design flexural strength shall be

In lieu of the preceding method, the following estimates of total losses may be used for prestressed members or structures of usual design. These loss values are based on use of normal weight concrete, normal prestress levels, and average exposure conditions. For exceptionally long spans, or for unusual designs, the method in Article 9.16.2.1 or a more exact method shall be used. TABLE 9.16.2.2 Estimate of Prestress Losses Type of Prestressing Steel Pretensioning Strand Post~Tensioninga Wire or Strand Bars

Total Loss f~

=

4,000 psi —

32,000 psi 22,000 psi

f~

=

5,000 psi

45,000 psi 33,000 psi 23,000 psi

Losses due to friction are excluded. Friction losses should be computed according to Article 9. t6. 1.

9.17 9.17.1

assumed as: tpM5 =1{A~f,*~d[l~0.6jPf~su +Asfsydt[l~0.6~~

IJI

~

PLI

___

(9-13a) 9.17.3

Flanged Sections

For sections having prestressing steel only, in which the depth of the equivalent rectangular stress block, defined as (A,rf~)/(0.85f~b’) is greater than the compression flange thickness ‘t,” and which satisfy Eq. (9-21), the design flexural strength shall be assumed as:

L

~

~M5 ~AIA sr f*d[1..061< A5~ f.~ sU b’dfjj

FLEXURAL STRENGTH General

+

Prestressed concrete members may be assumed to act as uncracked members subjected to combined axial and bending stresses within specified service loads. In calculations of section properties, the transformed area of

bonded reinforcement may be included in pretensioned members and in post-tensioned members after grouting; prior to bonding of tendons, areas of the open ducts shall be deducted. 9.17.2

9.16.2.2

0.85 f (b b’)(t)(d 0.5t)} —

sr f~ II +A,f,~(d, —d) b’df’

For rectangular or flanged sections having prestressing steel only, which the depth of the equivalent rectangular stress block, defined as (A~ f~)I(0.85 f~b), is not greater than the compression flange thickness “t”, and which satisfy Eq. (9-20), the design flexural strength shall be assumed as:

=

A!’f,’~d~l—0.6 Pf% ~

+

0.85 f~ (b b’)(t)(d 0.5t)} —

A Sr =A’~,— A,~ in Eq.

(9-13)

For rectangular or flanged sections with nonprestressed tension reinforcement included, in which the depth of the equivalent rectangular stress block, defined as (A’~’f~ + AJ,5)/(0.85 f~b), is not greater “t,”

and which

—

(9- 14a)

where:

A,,

than the compression flange thickness

(9-14)

For sections with non-prestressed tension reinforcement included, in which the depth of the equivalent rectangular stress block, defined as (A.J~)/(0.85 f~b’) is greater than the compression flange thickness “t,” and which satisfy Eq. (9-25), the design flexural strength shall be assumed as:

Rectangular Sections

c~M~

—

=

A~ +

(A,f,5/f~’~) in Eq. (9-14a)

A,f = 0.85 f~ (b — A,,

=

(9-14);

(9-15)

—

(9-ISa) (9-16)

the steel area required to develop the ultimate compressive strength of the overhanging por-

tions of the flange.

DIVISION I—DESIGN

9.17.4 9.17.4

207

and,

Steel Stress

9.17.4.1 Unless the value of ft can be more accurately known from detailed analysis, the following values may be used:

with prestressing only (as defined);

—c:Y ,r3 *

(9-21)

does not exceed 0.36I3~. (See Article 9.19 for reinforcement indices of sections with non-prestressed reinforcement.). For members with reinforcement indices greater than

Bonded Members...

f4l

A,,f~,/(b’df,~ for flanged sections)

Xp* f/f’)]

(9-17)

with non-prestressed tension reinforcement included; f~

0.36r3,, the design flexural strength shall be assumed not greater than: For rectangular sections: 4)M,

(9-17a)

=

2

4) [(0.36 [3

—

0.08 [3~)fbd

(9-22)

For flanged sections: 4)M.

Unbonded members ...ft=f,.

+

15,000

(9-18)

=

4)[(0.36[3 0.85 f, (b

0.08

— —

[3~)f~b’d2

b’) t (d

—

+

(9-23)

0.5t)]

provided that: (I) The stress-strain properties of the prestressing

steel approximate those specified in Division II, Article 10.3.1.1. (2) The effective prestress after losses is not less than

0 5 f’

9.18.2

Minimum Steel

9.18.2.1 The total amount of prestressed and nonprestressed reinforcement shall be adequate to develop an ultimate moment at the critical section at least 1 .2 times the cracking moment M~.

9.17.4.2 At ultimate load, the stress mn the prestressing steel of precast deck panels shall be limited to: where: fj~’ 1

D

3 ~

(9- 19) = (fr

+

f~~) S~

—

(SJS~

~

—

I)

shall be used for any Appropriate values for M~5, and Where beams are deintermediate composite sections. signed to be noncomposite, substitute S~ for S~ in the above equation for the calculation of My,. 5b

but shall

not be greater than ft as given by the equations

tnArticle 9.17.4.1. In the above equation:

D

= =

=

nominal diameter of strand in inches; effective stress in prestressing strand after losses in kips per square inch; distance from end of prestressing strand to center of panel in inches.

9.18.2.2 The minimum amount of non-prestressed longitudinal reinforcement provided in the cast-inplace portion of slabs utilizing precast prestressed deck panels shall be 0.25 square inch per foot of slab width.

9.18 9.18.1

DUCTILITY LIMITS Maximum Prestressing Steel

9.19

Prestressed concrete members shall be designed so that the steel is yielding as ultimate capacity is approached. In general, the reinforcement index shall be such that:

(p*ft /f for rectangular sections

(9-20)

NON-PRESTRESSED REINFORCEMENT

Non-prestressed reinforcement may be considered as contributing to the tensile strength of the beam at ultimate strength in an amount equal to its area times its yield point, provided that:

HIGHWAY BRIDGES

208 For rectangular sections:

~P5Y~di+K~u ]KPY~=036~

9.19

(9-24)

sections located at a distance less than h/2 from the face of the support may be designed for the same shear V, as that computed at a distance h12.

(9-25)

webs of precast segmental box girders to transfer erection shear. Possible reverse shearing stresses in the shear keys shall be investigated, particularly in segments near a pier. At time of erection, the shear stress carried by the shear key shall not exceed 2

9.20.1.5

For flanged sections: (A,f,5)/(b’df,’) —

+ (A,r f~)/(b ‘df~) = 0.36f3

(A~f)/(b’df~)

Design flexural strength shall be calculated based on Eq. (9-13a) or Eq. (9-14a) if these values are met, and on Eq. (9-22) or Eq. (9-23) if these values are exceeded.

9.20.2

Reinforced keys shall be provided in the

Shear-Strength Provided by Concrete

9.20.2.1 The shear strength provided by concrete, V~, shall be taken as the lesser of the values V, or

9.20 SHEAR* 9.20.2.2 The shear strength, V,,, shall be computed 9.20.1

General

by: V~

9.20.1.1 Prestressed concrete flexural members, except solid slabs and footings, shall be reinforced for shear and diagonal tension stresses. Voided slabs shall be inves-

=0.6

fb’d

+Vd+

tigated for shear, but shear reinforcement may be omitted

but need not be less than 1.7

if the factored shear force, V~, is less than half the shear strength provided by the concrete 4) V~.

taken less than 0.8h.

9.20.1.2 Web reinforcement shall consist of stirrups perpendicular to the axis of the member or welded wire fabric with wires located perpendicular to the axis of the member. Web reinforcement shall extend to a distance d from the extreme compression fiber and shall be carried as close to the compression and tension surfaces of the member as cover requirements and the proximity of other reinforcement permit. Web reinforcement shall be anchored at both ends for its design yield strength in accordance with the provisions of

I Y

Mer =—(6

f~ b’ d and d need not be

(9-28)

f’+f c

The maximum factored moment and factored shear at the section due to externally applied loads, M,,,, and V,, shall be computed from the load combination causing maximum moment at the section. 9.20.2.3

Members subject to shear shall be designed

(9-27)

The moment causing flexural cracking at the section due to externally applied loads, Me,, shall be computed by:

Article 8.27.

9.20.1.3

VM er M max

The shear strength, ~

by:

shall be computed

3.S Transition radius = 6 in. (c) 6 in. > Transition radius = 2 in. (d) 2 in. > Transition radius = 0 in.

T or Rev

—For all transition radii without end welds ground smooth.

T or Rev

E E

16

Detail base metal attached by full penetration groove welds

with a transition radius, R, regardless of the detail length and with weld soundness transverse to the direction of stress established by nondestructive inspection: —With equal plate thickness and reinforcement removed (a) Transition radius =24 in. (b) 24 in. > Transition radius = 6 in. (c) 6 in. > Transition radius = 2 in. (d) 2 in. > Transition radius = 0 in.

T or Rev

—With equal plate thickness and reinforcement not removed (a) Transition radius = 6 in. (b) 6 in. > Transition radius = 2 in. (c) 2 in. > Transition radius = 0 in. —With unequal plate thickness and reinforcement removed (a) Transition radius = 2 in. (b) 2 in. > Transition radius = 0 in.

T or Rev

—For all transition radii with unequal plate thickness and reinforcement not removed.

T or Rev

F

16

T or Rev T or Rev T or Rev

C

14

(b) Detail thickness > 0.5 in. Base metal at intermittent fillet welds.

See Noted

Shear stress on throat of fillet welds.

Shear

F

9

Base metal adjacent to details attached by fillet welds with

T or Rev

C

15,17,18,20

T or Rev

D

15,17

T or Rev T or Rev

F

7,9,15,17 7,9,15

Base metal at details connected with transversely loaded welds, with the welds perpendicular to the direction of stress: (a) Detail thickness 0.5 in. <

Fillet Welded Attachments-Longitudinally Loadedb,c.e

16

B C D

length, L, in the direction of stress, is less than 2 in. and stud-type shear connectors. Base metal adjacent to details attached by fillet welds with length, L, in the direction of stress, between 2 in. and 12 times the plate thickness but less than 4 in.

B C D

16

E 16

C D

E T or Rev

16 D E

F

Base metal adjacent to details attached by fillet welds with length, L, in the direction of stress greater than 12 times the plate thickness or greater than 4 in.: (a) Detail thickness K 1.0 in. (b) Detail thickness = 1.0 in.

)

10.6.2

DIVISION I—DESIGN

229

TABLE 10.3.1B (Continued)

General Condition

Stress Category (See Table lO.3.IA)

Kind of Stress

Situation

Illustrative Example (See Figure l0.3.IC)

Base metal adjacent to details attached by fillet welds with a transition radius, R, regardless of the detail length:

Fillet Welded Attachments— Transversely Loaded with the Weld in the Direction of Principal Stressb.e

Mechanically Fastened Connections

Eyebar or Pin Plates

—With the end welds ground smooth (a) Transition radius =2in. (b) 2 in. > Transition radius =0 in.

T or Rev

—For all transition radii without the end welds ground smooth.

TorRev

16 E E

Detail base metal attached by fillet welds with a transition radius, R, regardless of the detail length (shear stress on the throat of fillet welds governed by Category F): —With the end welds ground smooth

F

16

T or Rev

16 F

(a) Transition radius =2 in. —For (b) 2 in. ground allsmooth. >transition Transition radii radius without =0 the in. end welds

T or Rev

EF

16

Base metal at gross section of high-strength bolted slip resistant connections, except axially loaded joints which induce out-of-plane bending in connecting materials.

T or Rev

B

21

Base metal at net section of high-strength bolted bearing-type connections.

T or Rev

B

21

Base metal at net section of riveted connections.

T or Rev

D

21

Base metal at the net section of eyebar head, or pin plate Base metal in the shank of eyebars, or through the gross section of pin plates with: (a) rolled or smoothly ground surfaces (b) flame-cut edges

T

B

23, 24

T T

B B

23, 24 23,24

• T” signifies range in tensile stress only, “Rev” signifies a range of stress involving both tension and compression during a stress cycle. ““Longitudinally Loaded” signifies direction of applied stress is parallel to the longitudinal axis of the weld. “Transversely Loaded” signifies direction of applied stress is perpendicular to the longitudinal axis ofthe weld. ‘Transversely loaded partial penetration groove welds are prohibited. dAtlowable fatigue stress range on throat of fillet welds transversely loaded is a function ofthe effective throat and plate thickness. (See Frank and

Fisher, Journal ofthe Structural Division, ASCE, Vol. 105, No. 5T9, Sept. 1979.)

(

1411

‘-i--i —

0.06 +0.79Hlt~~

‘I

I

-~--1 K~

where S~ is equal to the allowable stress range for Category C given in Table 10.3. IA. This assumes no penetration at the weld root. rGusset plates attached to girder flange surfaces with only transverse fillet welds are prohibited. ~SeeWattar, Aibrecht and Sahli, Joumal of Structural Engineering, ASCE, Vol. III, No. 6, June 1985, pp. 1235—1249.

10.6.2 Members having simple or continuous spans preferably should be designed so that the deflection due to service live load plus impact shall not exceed ~ of the span. except on bridges in urban areas used in part by

pedestrians whereon the ratio preferably shall not exceed

10.6.3 The deflection of cantilever arms due to servince live load plus impact preferably should be limited to Y

5~

of the cantilever arm except for the case including pedestrian use, where the ratio preferably should be /~. 10.6.4 When spans have cross-bracing or diaphragms sufficient in depth or strength to ensure lateral distribution of loads, the deflection may be computed for the

standard H or HS loading (M or MS) considering all beams or stringers as acting together and having equal deflection.

10.6.4

HIGHWAY BRIDGES

230

12 2 Rad

C~)

13

C~) C

~aph

End, Tapered

Flano’-

7

18

8

23 (ifl

weg~ metal) 19

9 C

At End al Weld, Has No Length 24

) 10

FIGURE 1O.3.1C

Illustrative Examples

10.6.5

231

DIVISlON 1—DESIGN

TABLE l0.3.2A

TABLE 10.3.3A Temperature Zone Designations for Charpy V-Notch Impact Requirements

Stress Cycles

Main (Longitudinal) Load Carrying Members Truck Lane Type of Road Case AD’IT~ Loading Loading” 500,000 Freeways. Expressways, t 2,500 or 2,000,000’ Major Highways, and Streets

Minimum Service Temperature

Temperature Zone Designation

00F and above —l’Fto--30”F —31’Fto —600F

2 3

more

Freeways, Expressways, Major Highways, and Streets

It

Other Highways and Streets not included in Case I or II

ttl

less than 2,500

500,000

100,000

100,000

100,000

which the major stresses result from dead or live load, or both; and shall not exceed 140 for secondary members, or

those whose primary purpose is to brace the structure against lateral or longitudinal force, or to brace or reduce the unbraced length of other members, main or secondary.

Transverse Members and Details Subjected to Wheel Loads

Type of Road

Case

ADTT

Truck Loading

Freeways, Expressways, Major Highways, and Streets

1

2,500 or more

over 2,000,000

Freeways. Expressways, Major Highways, and Streets

II

less than 2,500

2,000,000

Other Highways and Streets

Ill

—

member as computed for the entire section with the KL/r ratio applicable thereto, both equal or exceed the computed total force that the member must sustain.

500,000

~AverageDaily Truck Traffic (one direction). “Longitudinal members should also be checked for truck loading. ‘Members shall also be investigated for “over 2 million’ stress cycles produced by placing a single truck on the bridge distributed to the girders as designated in Article 3.23.2 for one traffic lane loading.

The shear in steel girder webs shall not exceed 0.58 F~Dt,,C for this singie truck loading.

10.6.5 The moment of inertia of the gross cross-sectional area shall be used for computing the defiections of beams and girders. When the beam or girder is a part of a composite member, the service live load may be considered as acting upon the composite section. 10.6.6 The gross area of each truss member shall be used in computing deflections of trusses. If perforated plates are used, the effective area shall be the net volume divided by the length from center to center of perforations.

10.6.7 The foregoing requirements as they relate to beatn or girder bridges may be exceeded at the discretion t of the designer. 10.7

10.7.2 In determining the radius of gyration, r, for the purpose of applying the limitations of the KL/r ratio, the area of any portion of a member may be neglected provided that the strength of the member as calculated without using the area thus neglected and the strength of the

LIMITING I,ENGTHS OF MEMBERS

10.7.1 For con1pression members, the ‘,lendet ness ratio. KLJt. shall not exceed I 2() for main tnetnbers, or those in Dir considerations to be taken init account ss hen e \ccedi ng these limitations. reference is nude to ‘l3ulletin No. I ~J.Criteria tbr the t)e— Ileetion of Stee] Bridge~, as ailahie root the Atoericati lion and Steel Institute. ‘Nash ington. D.C

10.7.3

The radius of gyration and the effective area for carrying stress of a member containing perforated cover plates shall be computed for a transverse section through the maximum width of perforation. When perforations are staggered in opposite cover plates, the cross-sectional area of the member shall be considered the same as for a section having perforations in the same transverse plane. 10.7.4

Actual unbraced length, L, shall be assumed as

follows: For the top chords of half-through trusses, the length between panel points laterally supported as indicated under Article It). 16.12; for other main ti~enibers. the length between panel point intersections or centers of braced points or centers of end connections; for secondary members, the length between the centers of the end connections of such members or centers of braced points. 10.7.5 For tension members. excel)t rods. evebars. c ables, and plates. the ratio of unbraced length to radius of gyration shall nol exceed 200 for titain members, shall not exceed 240 for bracing members, and shall not exceed 140 for main members subject to a reversal of stress.

10.8

MINIMUM THICKNESS OF METAL

10.8.1 Structural steel (including bracing. cross fratimes. and all types of gLisset plates. except for webs of certain rolled shapes. closed ribs in orthotropic decks, fillers, and

HIGHWAY BRIDGES

232

in railings, shall be not less than Ys inch in thickness. The web thickness of rolled beams or channels shall not be less than 0.23 inches. The thickness of closed ribs in orthotropic decks shall not be less than Y 6 inch. 10.8.2 Where the metal will be exposed to marked corrosive influences, it shall be increased in thickness or specially protected against corrosion. It should be noted that there are other provisions in this section pertaining to thickness for fillers, segments of compression members, gusset plates, etc. As stated above, fillers need not be ~ inch minimum.

10.8.1

In main members carrying axial stress, 12 times the thickness. In bracing and other secondary members, 16 times the thickness. For other limitations, see Article 10.35.2. 10.11

EXPANSION AND CONTRACTION

10.8.3

10.8.4 For compression members, refer to “Trusses” (Article 10.16).

In all bridges, provisions shall be made in the design to resist thermal stresses induced, or means shall be provided for movement caused by temperature changes. Provmstons shall be made for changes in length of span resulting from live load stresses. In spans more than 300 feet long, allowance shall be made for expansion and contraction in the floor. The expansion end shall be secured against lat-

10.8.5 For stiffeners and other plates, refer to “Plate Girders” (Article 10.34).

eral movement.

10.8.6 For stiffeners and outstanding legs of angles, etc., refer to Article 10.10.

10.12

10.9

EFFECTIVE AREA OF ANGLES AND TEE SECTIONS IN TENSION

FLEXURAL MEMBERS

Flexural members shall be designed using the elastic section modulus except when utilizing compact sections under Strength Design as specified in Articles 10.48.1,

10.50.1.1, and 10.50.2.1. 10.9.1

The effective area of a single angel tension mem-

ber, a tee section tension member, or each angle of a double angle tension member in which the shapes are connected back to back on the same side of a gusset plate shall be assumed as the net area of the connected leg or flange plus one-half of the area of the outstanding leg.

10.13

COVER PLATES

10.13.1 The length of any cover plate added to a rolled beam shall be not less than (2d±3)feet, where (d) is the

depth of the beam in feet. 10.9.2

If a double angle or tee section tension member

ts connected with the angles or flanges back to back on op-

posite sides of a gusset plate, the full net area of the shapes shall be considered effective. When angles connect to separate gusset plates, as in the case of a double-webbed truss, and the angles are connected by stay plates located as near the gusset as practicable, or by other adequate means, the full net area of the

10.13.2

Partial length welded cover plates shall not be used on flanges more than 0.8 inches thick for nonredundant load path structures subjected to repetitive loadings that produce tension or reversal of stress in the member.

10.9.3

angles shall be considered effective. If the angles are not so connected, only 80 percent of the net areas shall be considered effective. 10.9.4

Lug angles may be considered as effective in

transmitting stress, provided they are connected with at least one-third more fasteners than required by the stress to be carried by the lug angle.

10.10 OUTSTANDING LEGS OF ANGLES The widths of outstanding legs of angles in compres-

ston (except where reinforced by plates) shall not exceed the following:

10.13.3 The maximum thickness of a single cover plate on a flange shall not be greater than two times the thickness of the flange to which the cover plate is attached. The

total thickness of all cover plates should not be greater than 2/2 times the flange thickness. 10.13.4 Any partial length welded cover plate shall extend beyond the theoretical end by the terminal distance, and it shall extend to a section where the stress ranee in the beam flange is equal to the allowable fatigue stress range for base metal adjacent to or connected by fillet welds. The theoretical end of the cover plate. when using service load design methods, is the section at which the stress in the flange without that cover plate equals the allowable service load stress, exclusive of fatigue considerations. When using strength design methods, the theoret-

DIVISION I—DESIGN

10. 13.4

233

ical end of the cover plate is the section at which the flange

mum yield point greater than 50,000 psi shall not be heat-

strength without that cover plate equals the required strength for the design loads, exclusive of fatigue requirements. The terminal distance is two times the nominal cover plate width for cover plates not welded across their ends, and l/s times for cover plates welded across their ends. The width at ends of tapered cover plates shall be not less than 3 inches. The weld connecting the cover

curved.

plate to the flange in its terminal distance shall be continuous and of sufficient size to develop a total stress of not less than the computed stress in the cover plate at its theoretical end. All welds connecting cover plates to beam flanges shall be continuous and shall not be smaller than the minimum size permitted by Article 10.23.2.

Minimum Radius of Curvature

10.15.2

10.15.2.1 For heat-curved beams and girders, the horizontal radius of curvature measured to the center line of the girder web shall not be less than 150 feet and shall not be less than the larger of the values calculated (at any and all cross sections throughout the length of the girder) from the following two equations: l4bD F~ ‘~ t

Any partial length end-bolted cover plate shall extend beyond the theoretical end by a terminal distance

(10-1)

10.13.5

7 SOOb

equal to the length of the end-bolted portion, and the cover plate shall extend to a section where the stressrange in the

beam flange is equal to the allowable fatigue stress range for base metal at ends of partial length welded cover plates with high-strength bolted, slip-critical end connections (Table 10.3. lB). Beams with end-bolted cover plates shall be fabricated in the following sequence: drill holes; clean

faying surfaces; install bolts; weld. The theoretical end of the end-bolted cover plate is determined in the same manner as that of a welded cover plate, as is specified in Article 10.13.4. The bolts in the slip-critical connections of the cover plate ends to the flange, shall be of sufficient numbers to develop a total force of not less than the computed force in the cover plate at the theoretical end. The slip resistance of the end-bolted connection shall be de-

termined in accordance with Article 10.32.3.2 for service load design, and 10.56.1.4 for load factor design. The lon-

gitudinal welds connecting the cover plate to the beam flange shall be continuous and stop a distance equal to one bolt spacing before the first row of bolts in the end-bolted portion. 10.14

(10-2)

In these equations, F, is the specified minimum yield point in kips per square inch of steel in the girder web, 4 is the ratio of the total cross-sectional area to the crosssectional area of both flanges, b is the widest flange width in inches, D is the clear distance between flanges in inches, t~ is the web thickness in inches. and R is the radius in inches. 10.15.2.2 In addition to the above requirements, the radius shall not be less than 1,000 feet when the flange thickness exceeds 3 inches or the flange width exceeds 30 inches. 10.15.3

Camber

To compensate for possible loss of camber of heatcurved girders in service as residual stresses dissipate, the amount of camber in inches, A at any section along the length L of the girder shall be equal to:

CAMBER

A= Girders should be cambered to compensate for dead

load deflections and vertical curvature required by profile

AR

grade.

A

OL(A+A)

(10-3)

AM

2F~(l,ooo—R~ 0.02_L EY~850) 0

AR —0 for radii greater than 1,000

10.15

10.15.1

HEAT-CURVED ROLLED BEAMS AND WELDED PLATE GIRDERS

Scope

This section pertains to rolled beams and welded I-section plate girders heat-curved to obtain a horizontal curvature. Steels that are manufactured to a specified mini-

where

AOL

is the camber in inches at any potnt along the

length L calculated by usual procedures to compensate for

deflection due to dead loads or any other specified loads; AM is the maximum value of AOL in inches within the length U; F is the modulus of elasticity in ksi; F~ is the

specified minimum yield point in ksi of the girder flange; Y 0 is the distance from the neutral axis to the extreme

HIGHWAY BRIDGES

234

outer fiber in inches (maximum distance for non-symmetrical sections); R is the radius of curvature in feet; and L is the span length for simple spans or for continuous spans, the distance between a simple end support and the dead load contraflexure point, or the distance between points of dead load contraflexure. (L is measured in inches.) Camber loss between dead load contraflexure points adjacent to piers is small and may be neglected.

10. 15.3

Channel sections, made with two angle segments. with

solid web, perforated web, or web of stay plates and lacing.

Single Box sections, mnade with side channels, beams, angles, and plates or side segments of plates only, connected top and bottom with perforated plates or stay plates and lacing.

Single Box sections. made with side channels, beams, Note: Part of the camnber loss is attributable to construetion loads and will occur during construction of the bridge; total camber loss will be complete after several months of in-service loads. Therefore a portion of the camber increase (approximately 50 percent) should be included in the bridge profile. Camber losses of this nature (but generally smaller in magnitude) are also known to occur in straight beams and girders. 10.16

10.16.1

TRUSSES

General

10.16.1.1

Component parts of individual truss metn-

hers may be connected by welds, rivets, or high-strength bolts. 10.16.1.2

Preference should be given to trusses with

single intersection web systems. Members shall be symmetrical about the central plane of the truss. 10.16.1.3 Trusses preferably shall have inclined end posts. Laterally unsupported hip joints shall be avoided. 10.16.1.4 Main trusses shall be spaced a sufficient distance apart, center to center, to be secure against overturning by the assumed lateral forces.

10.16.1.5 For the calculation of stresses, effective depths shall he assumed as follows: Riveted and bolted trusses, distance between centers of gravity of the chords.

Pin-connected trusses, distance between centers of chord pins. 10.16.2 Truss Members 10.16.2.1 Chord and web truss members shall usually be made in the following shapes:

angles and plates only. connected at top with solid cover plates and at the bottom with perforated plates or

stay plates and lacing. Double Box sections, made with side channels, beams, angles and plates or side segments of plates only, connected with a conventional solid web, together with top and bottom perforated cover plates or stay plates and lacing.

10.16.2.2 If the shape of the truss permits. compression chords shall be continuous. 10.16.2.3 In chords composed of angles in channelshaped members, the vertical legs of the angles preferably shall extend downward. 10.16.2.4 If web members are subject to reversal of stress, their end connections shall not be pinned. Counters preferably shall be rigid. Adjustable counters, if used. shall have open turnbuckles, and in the design of these members an allowance of 10,000 pounds per square inch shall be made for initial stress. Only one set of diagonals in any panel shall be adjustable. Sleeve nuts and loop bars shall not be used. 10.16.3

The design and details shall be such that secondary stresses will be as small as practicitble. Secondary stresses

due to truss distortion or floor beam deflection usually need not be considered in any member, the width of which, measured parallel to the plane of distortion. is less than one-tenth of its length. If the secondary stress exceeds 4,000 pounds per square inch for tension members and 3,000 for compression members, the excess shall be

treated as a primary stress. Stresses due to the flexural dead load moment of the member shall be considered as additional secondary stress. 10.16.4

“H” sections, made with two side segments (composed of angles or plates) with solid web, perforated web, or web of stay plates and lacing.

Secondary Stresses

Diaphragms

10.16.4.1 There shall be diaphragms in the trusses at the end connections of floor beams.

235

DIVISION I—DESIGN

10.16.4.2 10.16.4.2

The gusset plates engaging the pedestal pin

at the end of the truss shall be connected by a diaphragm. Similarly, the webs of the pedestal shall, if practicable, be

be proportioned to carry the entire upper lateral stress to the supports through the end posts of the truss.

connected by a diaphragm.

10.16.8 Perforated Cover Plates

10.16.4.3 There shall be a diaphragm between gusset plates engaging main members if the end tie plate is 4 feet or more from the point of intersection of the members.

When perforated cover plates are used, the followimsg provisions shall govern their design.

10.16.5

Camber

The length of the truss members shall be such that the camber will be equal to or greater than the deflection produced by the dead load. 10.16.6

Working Lines and Gravity Axes

10.16.6.1 Main members shall be proportioned so that their gravity axes will be as nearly as practicable in the center of the section.

10.16.6.2 In compressmon members of unsymmetrical section, such as chord sections formed of side segrnents and a cover plate, the gravity axis of the seetton shall coincide as nearly as practicable with the working line, except that eccentricity may be introduced to counteract dead load bending. In two-angle bottomn chord or diagonal members.~, the working line may be taken as the gage line nearest the back of the angle or at the center of gravity for welded trusses. 10.16.7

Portal and Sway Bracing

10.16.7.1 Through truss spans shall have portal bracing, preferably, of the two-plane or box type, rigidly connected to the end post and the top chord flanges~, and as deep as the clearance will allow. If a single plane portal is ttsed. it shall be located, preferably. in the central transverse plane of the end posts, with diaphragms between the webs of the posts to provide for a distribution of the portal stresses. The portal bracing shall be designed to take the full end reaction of the top chord lateral system. and the end posts shall be designed to transfer this reaction to the truss bearings. 10.16.7.2 Through truss spans shall have sway bracing 5 feet or more deep at each intermediate panel point. Top lateral struts shall be at least as deep as the top chord. 10.16.7.3 Deck truss spans shall have sway bracing in the plane of the end posts and at all intermediate panel points. This bracing shall extend the full depth of the trusses below the floor system. The end sway bracing shall

10.16.8.1 The ratio of length. in direction of stress. to width of perforation, shall not exceed two. 10.16.8.2 The clear distance between perforations in the direction of stress shall not be less than the distance between points of support. 10.16.8.3 The clear distance between the end perforation and the end of the cover plate shall not be less than 1 .25 times the distance between points of support.

10.16.8.4 The point of support shall be the inner line of fasteners or fillet welds connecting the perforated plate to the flanges. For plates butt welded to the flange edge of rolled segments, the point of support may be taken as the weld whenever the ratio of the outstanding flange width to flange thickness of the rolled segment is less than

seven. Otherwise, the point of support shall be the root of the flange of the rolled segment. 10.16.8.5 The periphery of the perforation at all points shall have a minimumn radius of 1’ inches. 10.16.8.6 10.16.9

For thickness of metal, see Article 10.3.9.2.

Stay Plates

10.16.9.1 Where the open sides of compression members are not connected by perforated plates. such members shall be provided with lacing bars and shall have stay plates as near each end as practicable. Stay plates shall be provided at intermediate points where the lacing ms tnterrupted. In main members. the length of the end stay plates between end fasteners shall be not less tharm I times the distance between points of support and the length of intermediate stay plates not less than of that distance. In lateral struts and other secondary mnemhers, the overall length of end and imitermediate stay plates shall be not less than of the distance between points of support.

10.16.9.2 The point of support shall be the inner line of fasteners or fillet welds connecting the stay plates to the flanges. For stay plates butt welded to the flange edge of

10. 16.9.2

HIGHWAY BRIDGES

236

rolled segments, the point of support may be taken as the weld whenever the ratio of outstanding flange width to

10.16.10.5 Lacing bars may be shapes or flat bars. For main members, the minimum thickness of flat bars

flange thickness of the rolled segment is less than seven. Otherwise, the point of support shall be the root of flange of rolled segment. When stay plates are butt welded to

shall be Vt of the distance along the bar between its connections for single lacing and ‘A for double lacing. For bracing members, the limits shall be ‘A for single lacing and i~ for double lacing.

rolled segments of a member, the allowable stress mn the member shall be determined in accordance with Article 10.3. Terminations of butt welds shall be ground smooth. 10.16.9.3 The separate segments of tension members composed of shapes may be connected by perforated plates or by stay plates or end stay plates and lacing. End stay plates shall have the same minmmum length as specified for end stay plates on main comnpression members, and intermediate stay plates shall have a minimum length of ‘A of that specified for intermediate stay plates on main compression members. The clear distance between stay plates on tension members shall not exceed 3 feet. 10.16.9.4 The thickness of stay plates shall be not

less than ‘A of the distance between points of support for main members, and ‘A of that distance for bracing members. Stay plates shall be connected by not less than three

fasteners on each side, and in members having lacing bars the last fastener in the stay plates preferably shall also pass through the end of the adjacent bar.

10.16.10.6

10.16.11

Gusset Plates

10.16.11.1

Lacing Bars

When lacing bars are used, the following provisions shall govern their design. 10.16.10.1 Lacing bars of compression members shall be so spaced that the slenderness ratio of the portion

the tnembers are pin-connected. The fastemlers connecting

each member shall be symmetrical with the axis of the member, so far as practicable, and the full development of the elements of the member shall be given consideration. The gusset plates shall be of ample thickness to resmst

shear, direct stress, and flexure acting on the weakest or critical section of maximum stress. 10.16.11.2 Re-entrant cuts, except curves made for appearance, shall be avoided as far as practicable.

10.16.11.4 Listed below are the values of the expression 11,000/ F~ for the following grades of steel:

36,000 psi, Y.P. Mm 58 50,000 psi, Y.P. Mm 49 70,000 psi, Y.P. Mm 42 90,000 psi, Y.P. Mm 37 100,000 psi, Y.P. Mm 35

10.16.10.2 The section of the lacing bars shall be determined by the formula for axial compression in which

10.16.10.3

If the distance across the member be-

tween fastener lines in the flanges is more than 15 inches and a bar with a single fastener in the connection is used, the lacing shall be double and fastened at the intersections. 10.16.10.4

The angle between the lacing bars and the

axms of the member shall be approximately 45 degrees for double lacing and 60 degrees for single lacing.

If the length of unsupported edge of

a gusset plate exceeds the value of the expressmon 11,000/ F~ times its thickness, the edge shall be stiffened.

of the flange included between the lacing bar connections will be not more than 40 or more than ‘A of the slenderness ratio of the member.

L is taken as the distance along the bar between its connections to the main segments for single lacing, and as 70 percent of that distance for double lacing.

Gusset or connection plates preferably

shall be used for connecting main members, except when

10.16.11.3 10.16.10

The diameter of fasteners in lacing bars

shall not exceed one-third the width of the bar. There shall be at least two fasteners in each end of lacing bars connected to flanges more than 5 inches in width.

10.16.12

Half-Through Truss Spans

10.16.12.1 The vertical truss members and the floor beams and their connections in half-through truss spans shall be proportioned to resist a lateral force of not less than 300 pounds per linear foot applied at the top chord panel points of each truss.

10.16.12.2

The top chord shall be considered as a

column with elastic lateral supports at the panel points. The critical buckling force of the column, so determined,

10. 16. 12.2

DIVISION I—DESIGN

shall exceed the maximum force from dead load, live load, and impact in any panel of the top chord by not less than

50 percent.* 10.16.13

Fastener Pitch in Ends of Compression Members

In the ends of compression members, the pitch of fasteners connecting the component parts of the member shall not exceed four times the diameter of the fastener for a length equal to 1 12 times the maximum width of the member. Beyond this point, the pitch shall be increased gradually for a length equal to 1/2 times the maximum width of the member until the maximum pitch is reached.

10.16.14

Net Section of Riveted or High-Strength Bolted Tension Members

10.16.14.1 The net section of a riveted or highstrength bolted tension member is the sum of the net sections of its component parts. The net section of a part is the product of the thickness of the part multiplied by its

237

10.16.14.5 When determining the unit stress on any least net width of either splice material or member being spliced, the amount of the stress previously transferred by fasteners adjacent to the section being investigated shall be considered in determining the unit stress on the net section. 10.16.14.6 The diameter of the hole shall be taken as Vt inch greater than the nominal diameter of the rivet or high-strength bolt, unless larger holes are permitted in accordance with Article 10.24.

10.17 BENTS AND TOWERS 10.17.1

General

Bents preferably shall be composed of two supporting columns, and the bents usually shall be united in pairs to form towers. The design of members for bents and towers is governed by applicable articles.

least net width.

10.17.2 Single Bents

10.16.14.2 The net width for any chain of holes extending progressively across the part shall be obtained by deducting from the gross width the sum of the diameters

Single bents shall have hinged ends or else shall be designed to resist bending.

of all the holes in the chain and adding, for each gage space in the chain, the quantity:

10.17.3 Batter Bents preferably shall have a sufficient spread at the

(10-4) 4g

where: S g

=

pitch of any two successive holes in the chain gage of the same holes.

The net section of the part is obtained frotn the chain that gives the least net width. 10.16.14.3 For angles, the gross width shall be the sum of the widths of the legs less the thickness. The gage for holes in opposite legs shall be the sum of gages from

base to prevent uplift under the assumed lateral loadings. In general, the width of a bent at its base shall be not less than one-third of its height.

10.17.4

Bracing

10.17.4.1 Towers shall be braced, both transversely and longitudinally, with stiff members having either welded, high-strength bolted or riveted connections. The sections of members of longitudinal bracing in each panel shall not be less than those of the members in corresponding panels of the transverse bracing.

back of angle less the thickness. 10.16.14.4 At a splice, the total stress in the member being spliced is transferred by fasteners to the splice material. *l~tsr a discitusion of columns with elastic lateral supports, refer to Tim— oshenko & Gere. ~Theory of Elastic Stability. McGraw-Hill First Edition. P. 122.

look Co.,

10.17.4.2 The bracing of long columns shall be designed to fix the column about both axes at or near the same point. 10.17.4.3 Horizontal diagonal bracing shall be placed in all towers having more than two vertical panels. at alternate intermediate panel points.

238

HIGHWAY BRIDGES

10.17.5

Bottom Struts

The bottom struts of towers shall be strong enough to

10. 17.5

10.18.1.4

Riveted and bolted flange angle splices

shall include two angles, one on each side of the flexural member.

slide the movable shoes with the structure unloaded, the

coefficient of friction being assumed at 0.25. Provision for expansion of the tower bracing shall be made in the column bearings.

10.18.2

10.18 SPLICES

ststed by the web and for the moment due to eccentricity of the shear introduced by the splice connection. Web

10.18.1

plates shall be spliced symmetrically by plates on each side. The splice plates for shear shall extend the full depth

General

10.18.1.1 The strength of members connected by high-strength bolts and rivets shall be determined by the gross section for compression members. For members primarily in bending, the gross section shall also be used, except that if more than 15 percent of each flange area is removed, that amount removed in excess of 15 percent shall

be deducted from the gross area. In no case shall the design tensile stress on the net section exceed 0.50 F,, when using service load design method or I .0 F,,, when using strength design method, where F, equals the minimum tensile strength of the steel, except that for M 270 Grades 100/100W steels the design tensile stress on the net seenon shall not exceed 0.46 F, when using the service load

design method. Splices may be made with rivets, by highstrength bolts, or by the use of welding. Splices, whether in tension, compression, bending, or shear, shall be designed in the case of service load design for a capacity based on not less than the average of the calculated design

stress at the point of splice and the allowable stress of the mrtember at the same point but, in any event, not less than 75 percent of the allowable stress in the member. Splices in the ease of strength design method shall be designed for

Beams and Girders

10.18.2.1 Web splice plates and their connections shall be designed for the portion of the design moment re-

of the girder between flanges. In the splice there shall be not less than two rows of rivets or bolts on each side of the

joint. 10.18.2.2 Flange splice plates need be designed only for the portion of the design moment not resisted by the web.

10.18.2.3

As an alternate, splices of rolled flexural

members may be proportioned for a shear equal to the actual maximum shear multiplied by the ratio of the splice design moment and the acttmal moment at the splice.

10.18.2.4 For riveted and bolted flexural members, splices in flange parts shall not be used between field splices except by special permission of the Engineer. In any one flange not more than one part shall be spliced at the same cross section. If practicable, splices shall be located at points where there is an excess of section. 10.18.2.5

In continuous spans, splices preferably

shall be made at or near points of contraflexure.

not less than the average of the required strength at the

point of splice and the strength of the member at the same point but, in any event, not less than 75 percent of the strength of the member. Where a section changes at a splice, the small section is to be used for the above splice requirements.

10.18.3

Columns

10.18.3.1. Compression members such as columns and chords shall have ends in close contact at riveted and bolted splices. Splices of such members which will be fabricated and erected with close inspection and detailed with

10.18.1.2 If splice plates are not in direct contact with the parts which they connect, the number of fasteners on each side of the joint shall be in excess of the number required for a direct contact splice to the extent of at

milled ends in full contact bearing at the splices may be held in place by means of splice plates and rivets or highstrength bolts proportioned for not less than 50 percent of the lower allowable design stress of the sections spliced.

least two extra transverse lines of fasteners for each intervening plate, except as provided in Article 10.18.1.3 and 10.18.6.

10.18.3.2 Splices in truss chords and columns shall be located as near to the panel points as practicable and usually on that side where the smaller stress occurs. The

10.18.1.3

Fillers in high strength bolted slip-critical connections need not be extended and developed, but eccentricity of forces at short, thick fillers must be considered.

arrangement of plates, angles. or other splice elements shall be such as to make proper provision for the stresses. both axial and bending, in the component parts of the members spliced.

10. 18.4

10.18.4

239

DIVISION I—DESIGN

Tension Members

10.18.4.1. For tension members and splice material, the gross section shall be used unless the net section area ts less than 85 percent of the corresponding gross area, in which ease that amount removed in excess of 15 percent shall be deducted from the gross area.

10.18.4.2 In no case shall the design tensile stress on the net section exceed 0.50 F, when using service load design or 1.0 F, when using strength design method, where F, equals the minimum tensile strength of the steel. 10.18.4.3 For M 270 Grades 100/100W steels, the design tensile stress on net section shall not exceed 0.46

10.18.6 Fillers When fasteners carrying loads pass through tillers thicker than inch, except in high-strength bolted connections designed as slip-critical connections, the fillers shall be extended beyond the splice material and the filler extensmon shall be secured by enough additional fasteners to distribute the total stress in the member uniformly over the combined section of the member and the filler. A5 an alternate, an equivalent number of additional fasteners may be passed through the gusset or splice material without extending the filler. Fillers /~ inch or more in thickness shall consist of not more than two plates, unless special permission is given by the Engineer. /4

F,, when using service load design method.

10.19 STRENGTH OF CONNECTIONS

10.18.4.4 For calculating the net section, the provismons of Article 10.16.14 shall apply.

10.19.1

10.18.5

Welding

10.18.5.1 Tension and compression members may be spliced by means of full penetration butt welds, preferably without the use of splice plates. 10.18.5.2 Welded field splices preferably shotmld be arranged to mtnmtntze overhead welding. 10.18.5.3

In welded splices any tiller Vt inch or more

mn thickness shall extend beyond the edges of the splice plate and shall be welded to the part on which it is fitted, with sufficient weld to transmit the splice plate load applied at the surface of the filler as an eccentric load. 10.18.5.4 The welds joining the splice plate to the filler shall be sufficient to transmit the splice plate load and shall be long enough to avoid overloading the filler along the toe of the weld. Any filler less than Vt inch thick shall have its edges made flush with the edges of the splice plate. The weld size necessary to carry the splice plate load shall be increased by the thickness of the filler plate.

General

10.19.1.1 Except as otherwise provided herein, connections for main members shall be designed in the case of service load design for a capacity based on not less than the average of the calculated design stress in the member at the point of connection and the allowable stress of the member at the same point but, in any event, not less than 75 percent of the allowable stress in the metnber. Connections for main members in the case of load factor design shall be designed for not less than the average of the required strength at the point of connection and the

strength of the member at the same point but, in any event, not less than 75 percent of the strength of the member. 10.19.1.2 Connections shall be made symmetrical about the axis of the members insofar as practicable. Connections, except for lacing bars and handrails, shall contain not less than two fasteners or equivalent weld. 10.19.1.3 Members, including bracing, preferably shall be so connected that their gravity axes will intersect in a point. Eccentric connections shall be avoided, if practicable, but if unavoidable the members shall be so proportioned that the combined fiber stresses will not exceed the allowed axial design stress. 10.19.1.4

10.18.5.5 Material of different widths spliced by butt welds shall have transitions conforming to Figure 10. 1 8.5A. The type transition selected shall be consistent with the Fatigue Stress Category from Table 10.3.1 B for the Groove Welded Connection used in the design of the memnber. At butt-welded splices joining pieces of different thicknesses, there shall be a uniform slope between

the offset surfaces, including the weld, of not more than I in 2/2.

In the case of connections which transfer

total member shear at the end of the member, the gross

section shall be taken as the gross. .section of the connected elements. 10.19.2

End Connections of Floor Beams and Stringers

10.19.2.1 The end connection shall be designed for the calculated member loads. The end connection angles

10.19.2.1

HIGHWAY BRIDGES

240

DETAIL OF WIDTH TRANSITION

2½

(b) Straight Tapered Transition

(a) 2-0’ Radius Transition FIGURE l0.18.SA Splice Details

of floor beams and stringers shall be not less than /~ inch in finished thickness. Except in cases of special end floor beam details, each end connection for floor beams and stringers shall be made with two angles. The length of these angles shall be as great as the flanges will permit. Bracket or shelf angles which may be used to furnish support during erection shall not be considered in deter-

10.19.2.4 Where timber stringers frame into steel floor beams, shelfangles with stiffeners shall be provided to carry the total reaction. Shelf angles shall be not less than ~ inch thick.

10.19.3

mining the number of fasteners required to transmit end shear. 10.19.2.2 End-connection details shall be designed with special care to provide clearance for making the field connection.

End Connections of Diaphragms and Cross Frames

10.19.3.1 The end connections for diaphragms or cross frames in straight rolled-beam and plate-girder bridges shall be designed for the calculated member loads.

10.19.2.3 End connections of stringers and floor beams preferably shall be bolted with high-strength bolts; welded end connections, they shall be designed for the vertical loads and the end-bending moment resulting from

10.19.3.2 Vertical connection plates such as transverse stiffeners which connect diaphragms or cross frames to the beam or girder shall be rigidly connected to

the deflection of the members.

both top and bottom flanges.

however, they may be riveted or welded. In the case of

10.20

241

DIVISION I—DESIGN

10.20 DIAPHRAGMS AND CROSS FRAMES 10.20.1

L

General

bf

Rolled beam and plate girder spans shall be provided

with cross frames or diaphragms at each support and with intermediate cross frames or diaphragms placed in all bays and spaced at intervals not to exceed 25 feet. Diaphragms for rolled beams shall be at least Vt and preferably the beam depth and for plate girders shall be at least and preferably Vt the girder depth. Cross frames shall be as deep as practicable. Intermediate cross frames shall preferably be of the cross type or vee type. End cross frames or diaphragms shall be proportioned to adequately transmit all the lateral forces to the bearings. Intermediate cross frames shall be normal to the main members when the supports are skewed more than twenty degrees (200). Cross frames on horizontally curved steel girder bridges shall be designed as main members with adequate provisions for transfer of lateral forces from the girder flanges. Cross frames and diaphragms shall be designed for horizontal wind forces as described in Article 10.21.2.

=

span length (ft)

=

thickness of flange (in.)

=

width of flange (in.)

10.20.2.2

Diaphragms and Cross Frames

The maximum horizontal force (F0) in the transverse diaphragms and cross frames is obtained from the following:

/2

/2

10.20.2 Stresses Due to Wind Loading When Top Flanges are Continuously Supported 10.20.2.1

F0

=

I. l4WS~ with or without bracing

10.20.3

(10-10)

Stresses Due to Wind Load When Top Flanges are not Continuously Supported

The stress shall be computed using the structural system in the plane of the flanges under consideration. 10.21

LATERAL BRACING

10.21.1 The need for lateral bracing shall be investigated. Flanges attached to concrete decks or other decks of comparable rigidity will not require lateral bracing. 10.21.2

A horizontal wind force of 50 pounds per

square foot shall be applied to the area of the super-

structure exposed in elevation. Half of this force shall be Flanges

applied in the plane of each flange. The stress induced

shall be computed in accordance with Article 10.20.2.1. The maximum induced stresses, F, in the bottom flange of each girder in the system can be computed from the following: F

=

RFCS

(10-5) where:

R=

[0.2272L

—

C

II] 52/3

when no bottom lateral bracing is provided

)

(10-6)

C

R = [0.059L —0.64] S~ 112

when bottom lateral bracing is provided

)

(10-7)

The allowable stress shall be factored in accordance with

Article 3.22. 10.21.3 When required, lateral bracing shall be placed in the exterior bays between diaphragms or cross-frames. All required lateral bracing shall be placed in or near the plane of the flange being braced. 10.21.4 Where beams or girders comprise the main members of through spans, such members shall be stiffened against lateral deformation by means of gusset plates

or knee braces with solid webs which shall be connected to the stiffeners on the main members and the floor beams. If the unsupported length of the edge of the gusset plate

(or solid web) exceeds 60 times its thickness, the plate or web shall have a stiffening plate or angles connected

along its unsupported edge. Fcb=

M.b

—

72M ~h

fbf

(psi)

.08WS~(ft-lb)

(10-8) 10.21.5

Through truss spans, deck truss spans, and spandrel braced arches shall have top and bottom lateral

(10-9)

W

=

wind loading along the exterior flange (lb/ft)

Sa

=

diaphragm spacing (ft)

bracing. 10.21.6 Bracing shall be composed of angles, other shapes, or welded sections. The smallest angle used in

242

HIGHWAY BRIDGES

10.2 1.6

bracing shall be 3 by 2/! inches. There shall be not less

lowed in Article 10.32, The maximum size that may be

than two fasteners or equivalent weld in each end connection of the angles.

used along edges of connected parts shall be:

tems may be considered effective simultaneously if the members meet the requirements both as tension and compression members. The members shall be connected at

(I) Along edges of material less than Vt inch thick, the maximum size may be equal to the thickness of the material. (2) Along edges of material Vt inch or more in thickness, the maximum size shall be /, inch less than the

their intersections.

thickness of the material, unless the weld is especially

10.21.7

If a double system of bracing is used, both sys-

designated on the drawings to be built out to obtain full

10.21.8 The lateral bracing of compression chords preferably shall be as deep as the chords and effectively

throat thickness.

connected to both flanges.

10.23.2.2

10.22 10.22.1

CLOSED SECTIONS AND POCKETS

The minimum fillet weld size shall be as shown in the following table.**

Closed sections and pockets or depressions that

will retain water, shall be avoided where practicable. Pockets shall be provided with effective drain holes or be filled with waterproofing material. 10.22.2

Details shall be so arranged that the destructive

Minimum Size of Fillet Welds

Base Metal Thickness of

Minimum Size

Thicker Part Jointed (T)

of Fillet Weld*

in.

mm

T=3/4 3/4 0.33

2

(10-16)

F1’=F~ I— (f~/F~)

which it bears. When parts in contact have different yield points, F~ shall be the smaller value.

following formulas: Diameters up to 25 inches: F~ —13,000

20,000

F,

=

computed rivet or bolt shear stress in shear, ksi; allowable shear stress on rivet or bolt from Table l0.32.3A or Table l0.32.3B, ksi;

F,

=

allowable tensile stress on rivet or bolt from

F~ —13,000 20,000

reduced allowable tensile stress on rivet or bolt due to the applied shear stress, ksi. 2

= =

S k

= =

+ (kt)2

=

(10-17)

600d

(10-18)

3,000 d

(10-19)

Diameters 25 to 125 inches:

Table I 0.32.3A or Table I 0.32.3B, ksi;

s

44.0 34.0

10.32.4 Pins, Rollers, and Expansion Rockers

where:

=

47

10.32.4.2 Bearing per linear inch on expansion rockers and rollers shall not exceed the values obtained by the

0 33 =

=

38 35.5 27.5

10.32.4.1 The effective bearing area of a pin shall be its diameter multiplied by the thickness of the material on

10.32.3.3.4 Where rivets or high-strength bolts are subject to both shear and tension, the tensile stress shall not exceed the value obtained from the following equations:

for f,IF

A 325)

More than 500,000

F~= 120 ksi for M 164 (A 325) bolts up to I-inch diameter; = 105 ksi for M 164 (A 325) bolts over I-inch =

Number of Cycles

AASHTO M 253 (ASTM A 490)

where:

p

=

allowable bearing in pounds per linear inch;

d

=

diameter of rocker or roller in inches;

=

minimum yield point in tension of steel in

the computed rivet or bolt unit stress in shear;

the roller or bearing plate, whichever is the

the computed rivet or bolt unit stress in tension, including any stress due to prying action;

smaller.

the allowable rivet or bolt unit stress in shear; a constant: 0.75 for rivets; 0.6 for high-strength

Expansion rollers shall be not less than 4 inches in diam-

bolts with thread excluded from shear plane.

eter.

10.32.3.4

Fatigue

When subject to tensile fatigue loading, the tensile stress in the bolt due to the service load plus the prying force resulting from application of service load

10.32.4.3 Design stresses for Steel Bars. Carbon Cold Finished Standard Quality, AASHTO M 169 (ASTM A 108), and Steel Forgings, Carbon and Alloy, for General Industrial Use. AASHTO M 102 (ASTM A 668), are given in Table l0.32.4.3A.

255

DIVISION I—DESIGN

10.32.4.3

Allowable Stresses—Steel Bars and Steel Forgings

TABLE 1032.4.3A

AASHTO Designation with Size

—

Limitations ASTM Designation Grade or Class

Minimum Yield Point, psi

Ml694tn.tn M 102 To 20 M 102 To 20 M 102 To 10 M 102 To 20 dia. or less tn. tn dia. in. india. in. india. in. in dia. A108 Grades 1016 1030 mcI.

A 668

A 668

Class C

Class D

A 668 Class F

A

36,000”

33,000

37,500

50,000

50,000

29,000”

26,000

30,000

40,000

40,000

668b

Class G

Stress in Extreme Fiber, psi

O.80F~

Shear, psi

0.40F~

14,000”

13,000

15,000

20,000

20,000

Bearing on Pins not Subject to Rotation,

0.80F~

29,000”

26,000

30,000

40,000

40,000

0.40F~

14,000”

13,000

15,000

20,000

psi’ Bearing on Pins Subject to Rotation, psi

(such as used in rockers and hinges)

20,000

“For design purposes only. Not a part of the A 108 specifications. Supplementary material requirements sbould provide guarantee that material will

meet these values. “May substitute rolled material of the same properties. ‘This shall apply to pins used primarily in axially loaded members, such as truss members and cable adjusting links. It shall not apply to pins used

in members having rotation caused by expansion or deflection.

1032.5

Cast Steel, Ductile Iron Castings, Malleable Castings, and Cast Iron

10.32.5.3

Cast Iron

Cast iron castings shall conform to specifications for 10.32.5.1

Cast Steel and Ductile [ron

Gray Iron Castings, AASHTO M 105 (ASTM A 48). Class 30B. The following allowable stresses in pounds per

10.32.5.1.1 For cast steel conforming to specifications for Steel Castings for Highway Bridges, AASHTO M 192 (ASTM A 486), Mild-to-MediumStrength Carbon-Steel Castings for General Application, AASHTO M 103 (ASTM A 27), and Corrosion-Resistant

Iron-Chromium, Iron-Chromium-Nickel and NickelBased Alloy Castings for General Application, AASHTO M 163 (ASTM A 743), and for Ductile Iron Casttngs (ASTM A 536), the allowable stresses in pounds

per square inch shall be in accordance with Table 10.32.5. IA. 10.32.5.1.2 When in contact with castings or steel of a different yield point, the allowable unit bearing stress of

the material with the lower yield point shall govern. For riveted or bolted connections, Article 10.32.3 shall govern. 10.32.5.2

Malleable castings shall conform to specifications for Malleable Iron Castings. ASTM A 47 Grade 35018. The following allowable stresses in pounds per square inch

shall be used: . .

.

.

Bending in Extreme Fiber Shear

Direct Compression, Short Columns

. .

18,000 18,000 25,000,000 .

3,000 3,000

12,000

10.32.5.4 Bronze or Copper-Alloy 10.32.5.4.1

Bronze castings, AASHTO M

107

(ASTM B 22), Copper Alloys 913 or 911, or CopperAlloy Plates, AASHTO M 108 (ASTM B 100), shall be specified. 10.32.5.4.2

The allowable unit-bearing stress in

pounds per square inch on bronze castings or copper-alloy plates shall be 2,000. 10.32.6

Malleable Castings

Tension Bending in Extreme Fiber Modulus of Elasticity

square inch shall be used:

Bearing on Masonry

10.32.6.1 The allowable unit-bearing stress in pounds per square inch on the following types of masonry shall be: Granite Sandstone and Limestone

800 400

10.32.6.2 The above bridge seat unit stress will apply only where the edge of the bridge seat projects at least 3

HIGHWAY BRIDGES

256 TABLE 1032.5AA

10.32.6.3

Allowable Stresses—Cast Steel and Ductile Iron

AASI-ITO Designation ASTM Designation

M 103 A 27

M 192 A 486

Class or Grade

70-36 70 36,000

M 192 A 486

None

M 163 A 743

A 536

90 120 60,000 95,000

CA-15 60-40-18 65,000 40,000

14,500 14,500 20,000 20,000

22,500 22,500 30,000 30,000

34,000 34,000 45,000 45,000

24,000

Shear Bearing, Steel Parts in Contact

9,000 30,000

13,500 45,000

Bearing on Pins not Subject to Rotation Bearing on Pins Subject to Rotation

26,000 13,000

40,000 20,000

Minimum Yield Point, F~ Axial Tension Tension in Extreme Fibers Axial Compression, Short Columns Compression in Extreme Fibers

24,000

16,000 16,000

32,000

22,000

32,000

22,000

21,000 68,000

14,000 48,000

10,000 33,000

60,000 30,000

43,000 21,500

28,000 14,000

(such as used in rockers and hinges) inches (average) beyond the edge of shoe or plate. Otherwise, the unit stresses permitted will be 75 percent of the above amounts. 10.32.6.3 For allowable unit-bearing stress on concrete masotirv. refer to Article 8 1 9 2 1 3

10.33

that flange. That area in excess of 15 percent shall be deducted from the gross area.

10.34.1.2 The compression flanges of plate girders supporting timber floors shall not be considered to be laterally supported by the flooring ttnless the floor and fastenings are specially designed to provide support.

ROLLED BEAMS 10.34.2 Flanges

10.33.1

General 10.34.2.1

Welded Girders

10.33.1.1

Rolled beams, including those with welded cover plates, shall be designed by the moment of inertia method. Rolled beams with riveted cover plates shall be designed on the same basis as riveted plate girders.

10.33.1.2 The compression flanges of rolled beams supporting timber floors shall not be considered to be laterally supported by the flooring unless the floor and fastenings are specially designed to provide adequate support.

10.34.2. 1.1 Each flange may comprise a series of plates joined end to end by full penetration butt welds. Changes in flange areas may be accomplished by varying the thickness and/or width of the flange plate, or by adding cover plates. Where plates of varying thicknesses or widths are connected, the splice shall be made in accordance with Article 10. 18 and welds ground smooth before attaching to the web.

10.33.2

10.34.2.1.2 When cover plates are used, they shall be designed in accordance with Article 10.13.

Bearing StitTeners

Suitable stiffeners shall be provided to stiffen the webs of rolled beams at bearings when the unit shear in the web adjacent to the bearing exceeds 75 percent of the allowable shear for girder webs. See the related provisions of Article 10.34.6. 10.34

10.34.1

10.34.2.1.3 The ratio of compression flange plate width to thickness shall not exceed the value determined by the formula: b

PLATE GIRDERS

General

10.34.1.1 Girders shall he proportioned by the moment of inertia method. For members primarily in bending. the entire gross seetton shall be used when calculating tensile and compressive stresses. Holes for high-strength bolts or rivets and/or open holes not exceeding 1’/4 inches, may be neglected provided the area removed from each flange does not exceed 15 percent of

3,250

but in no case shall

(10-20)

b/t exceed 24 10.34.2.1.4 Where the calculated compressive bending stress equals .55 F~ the (bit) ratios for the various grades of steel shall not exceed the following: 36.000 psi, Y.P. Mm. bit

50,000 psi, Y.P Mm. b/t

_

= 20

psi, Y.P. Mm. bit = 17 90,000 psi, Y.P. Mm. bit 15 100,000 psi, Y.P. Mm. b/t 14 70,000

10.34.2.1.4

DIVISION I—DESIGN

In the above b is the flange plate width, t is the thickness, and fh is the calculated maximum compressive bending stress. (See Article 10.40.3 for Hybrid Girders.) 10.34.2.1.5 In the case of a composite girder the ratio of the top compression flange plate width to thickness shall not exceed the value determined by the formula:

257

10.34.2.2.5 The gross area of the compression flange, except for composite design. shall be not less than the gross area of the tension flange. 10.34.2.2.6 Flange plates shall be of equal thickness. or shall decrease in thickness from the flange angles outward. No plate shall have a thickness greater than that of

the flange angles. b

3,250

t

t(¶fl

but in no case shall

b/t exceed 24

(10- 21)

10.34.2.2.7

At

least one cover plate of the top

flange shall extend the full length of the girder except where t~

1 is the top flange compressive stress due to noncomposite dead load.

10.34.2.2

Riveted or Bolted Girders

10.34.2.2.1 Flange angles shall form as large a part of the area of the flange as practicable. Side plates 7/s shall inch not be used except where flange angles exceeding in thickness otherwise would be required. 10.34.2.2.2 Width of outstanding legs of flange angles in compression, except those reinforced by plates, shall not exceed the value determined by the formula: b’

_

1,625

but in no case shall b’/t exceed 12

when the flange is covered with concrete. Any coverplate that is not full length shall extend beyond the theoretical cutoff point far enough to develop the capacity of the plate or shall extend to a section where the stress in the remainder of the girder flange is equal to the allowable fatigue stress, whichever is greater. The theoretical cutoff point of the cover plate is the section at which the stress in the flange without that cover plate equals the allowable stress, exclusive of fatigue considerations. /0.34.2.2.8 The number of fasteners connecting the flange angles to the web plate shall be sufficient to develop the increment of flange stress transmitted to the flange angles, combined with any load that is applied directly to the flange.

(10-22)

10.34.2.2.3 Where the calculated compressive bending stress equals 0.55 F 5, the b’/t ratios for the various grades of steel shall not exceed the following:

10.34.2.2.9 Legs of angles 6 inches or greater in width, connected to web plates, shall have two lines of fasteners. Cover plates over 14 inches wide shall have four lines of fasteners.

10.34.3 36,000 psi, Y.P. Mm. b/t 50,000 psi, Y.P. Mm. h’/t 70,000 psi, Y.P. Mi b’/t

= =

8.5

90,000 psi, Y.P. Mm. b’/t

=

7.5

=

7

100,000

psi, Y.P. Mi

b/t

II 10

10.34.3.1

1,625

7~ Jfm

but in no case shall b’/t exceed 12

Girders Not Stiffened Longitudinally

10.34.3.1.1 The web plate thickness of plate girders without longitudinal stiffeners shall not be less than that determined by the formula:

10.34.2.2.4 In the case of a composite girder the width of outstanding legs of top flange angles in compression, except those reinforced by plates. shall not exceed the value determined by the following formula: b’

Thickness of Web Plates

(10- 23)

In the above b’ is the width of a flange angle, t is the thickness. f1, is the calculated maximum compressmve stress. and f~~1 is the top flange compressive stress due to noncomposite dead load.

=

(See Figure l0.34.3.IA.) (10-24)

but in no case shall the thickness be less than D/170. 10.34.3.1.2 Where the calculated compressive bending stress in the flange equals the allowable bending stress, the thickness of the web plate (with the web stiffened or not stiffened, depending on the requirements for transverse stiffeners) shall not be less than (where the Y.P. is for the flange material):

HIGHWAY BRIDGES

258 36,000 psi, Y.P. 50,000 psi, Y.P. 70,000 psi, Y.P. 90,000 psi, Y.P. 100,000 psi, YP.

10.34.3.2

Mi

D/165

Mi

D/140

Mi Mi Mm

D/l 15 D/105 D/100

10.34.3.1.2

in combination with one longitudinal stiffener shall not be less than (where the Y.P. is for the flange material): 36,000 psi, Y.P. 50,000 psi, Y.P. 70,000 psi, Y.P. 90,000 psi,Y.P.

Girders Stiffened Longitudinally

Mm. Mm. Mm. Mi

100,000 psi,Y.P. Mi 10.34.3.2. 1 The web plate thickness of plate girders equipped with longitudinal stiffeners shall not be less than that determined by the formula: D ~b 46,000 (See Figure l0.34.3.IA) (10-25)

D/330 D/280 D/230 D/210

D/200

In the above, D (depth of web) is the clear unsupported distance in inches between flange components, t~, is the web thickness, and f 5 is the calculated flange bending stress.

10.34.4 Transverse Intermediate Stiffeners but in no case shall the thickness be less than D/340. 10.34.3.2.2 Where the calculated bending stress in the flange equals the allowable bending stress, the thickness of the web plate stiffened with transverse stiffeners

10.34.4.1 Transverse intermediate stiffeners may be omitted if the average calculated unit-shearing stress in the gross section of the web plate at the point considered, f~, is less than the value given by the following equation: 7 F= 733x10 (D/t~)2

260

F~ 3

(10-26)

4’ ‘“T

: j1L~

fjL~

0

where:

D

F,

=

unsupported depth of web plate between flanges in inches;

=

thickness of the web plate in inches;

=

allowable shear stress in psm.

180

0 80

0,0)

160

a U’.-

10.34.4.2 Where transverse intermediate stiffeners are required, the spacing of the transverse intermediate stiffener shall be such that the actual shearing stress will not exceed the value given by the following equation; the maximum spacing is further limited to 3D and is subject to the handling requirement below:

n ~

a

0)C

50)

0

0.87(1 —C)

00

o 11Lli 10

30

20

30

I .1 1 L2~ 40 50

~b (ks’l

The constant C is equal to the buckling shear stress divided by the shear yield stress, and is determined as follows:

(a function of bending stress) depth of web thickness of web

for

D

6,000 k

—<

calculated compressive bending stress in flange

FIGURE 10.343.IA.

(10-27)

60

WEB THICKNESS AND GIRDER DEPTH

o

1

Web Thickness vs. Girder Depth

C = 1.0

DIVISION I—DESIGN

10.34.4.2

10.34.4.5 Where the calculated shear stress equals the allowable shear stress, transverse intermediate stiffeners may be omitted if the thickness of the web is riot less than:

for: 6,000

k=(D/

)=7~500 k (10-28)

6,000

k

(D/t~)

F~

for

D/t~

7,500

7k C— (Dit~)2F~ 4.5x10 where:

=

F:, =

36,000 psi, YP. 50,000 psi, YP. 70,000 psi, Y.P. 90,000 psi, Y.P. 100,000 psi, YP. 10.34.4.6

k (10- 28A)

k=5÷ (d

(10- 28B)

2

0 /D) spacing of intermediate stiffener yield strength of the web plate

(F~/3) in Equation (10-27) can be replaced by the allowable shearing stress given in Table 10.32.1 A. Transverse stiffeners shall be required if Dit~~ is greater than 150. For panels without longitudinal stiffeners, the spacing of these stiffeners shall not exceed D1260/(D/tv)] to ensure efficient handling, fabrication, and erection of the girders.

= CF~/3

=F~/3

I

=

J

=

D

=

=

unsupported depth of web plate between flange components in inches for transversely stiffened girders, or maximum subpanel depth in inches for longitudinally stiffened girders; thickness of the web plate in inches.

The gross cross-sectional area of intermediate transverse stiffeners shall be greater than:

average calculated unit-shearing stress at the section; live load shall be the load to produce maximum moment at the section under consideration

F,

minimum permissible moment of inertia of any type of transverse intermediate stiffener in mnches4; required ratio of rigidity of one transverse stiffener to that of the web plate;

(10-30)

where:

f.

= 2.5

actual distance between stiffeners in inches~

=

=

.34f~/F~)F:,

(10-31)

= d,.,t~J

(D/d 2 — 2, but not less than 0.5 (10-32) 0) In these expressions,

tude of the shear stress higher than 0.6 F~, the bending stress, F~, shall be limited to:

(.754 —

Intermediate stiffeners preferably shall be

where:

ous action of shear and bending moment with the magni-

=

D/66 D156 D/50 D/47

I

(10-29)

If a girder panel is subjected to simultane-

Mi Mi Mi Mi

10.34.4.7 The moment of inertia of any type of transverse stiffener with reference to the mid-plane of the web shall not be less than:

=

10.34.4.4

Mm. D/78

made of plates for welded plate girders and shall be made of angles for riveted plate girders. They may be in pairs, one stiffener fastened on each side of the web plate, with a tight fit at the compression flange. They may, however, be made of a single stiffener fastened to one side of the web plate. Stiffeners provided on only one side of the web must be in bearing against, but need not be attached to, the compression flange for the stiffener to be effective. However, transverse stiffeners which connect diaphragms or crossframes to the beam or girder shall be rigidly connected to both the top and bottom flanges.

J

10.34.4.3 The spacing of the first intermediate stiffener at the simple support end of a girder shall be such that the shearing stress in the end panel shall not exceed the value given by the following equation (the maximum spacing is limited to I SD): F.

259

value obtained from Equation (10-27).

A

= [0.I5BDt 0(l

— C)

(fiR.)

—

18 t~.JY

(l0-32a)

where Y is the ratio of web plate yield strength to stiffener plate yield strength: B = 1.0 for stiffener pairs, 1.8 for sin-

260

HIGHWAY BRIDGES

gle angles, and 2.4 for single plates; and C is computed by Article 10.34.4.2. When values computed by Equation (l0-32a) approach zero or are negative, then transverse stiffeners need only meet the requirements of Equation (10-31), and the requirements of Article 10.34.4.10.

10.34.4.8 When stiffeners are in pairs, the moment of inertia shall be taken about the center line of the web plate. When single stiffeners are used, the moment of inertia shall be taken about the face in contact with the web plate. 10.34.4.9 Transverse intermediate stiffeners need not be in bearing with the tension flange. The distance between the end of the stiffener weld and the near edge of the web-to-flange fillet welds shall not be less than 4tv or more than 6t~. Stiffeners at points of concentrated loading shall be placed in pairs and should be designed in accordance with Article 10.34.6. However, transverse stiffeners which connect diaphragms or crossframes to the beam or girder shall be rigidly connected to both the top and bottom flanges. 10.34.4. 10

The width of a plate or the outstanding

leg of an angle intermediate stiffener shall not be less than 2 inches plus ‘A the depth of the girder, and it shall preferably not be less than ‘/4 the full width of the girder flange. The thickness of a plate or the outstanding leg of an angle intermediate stiffener shall not be less than ‘/16 its width. Intermediate stiffeners may be AASHTO M 270 Grade 36 steel.

10.34.5

Longitudinal Stiffeners

10.34.5.1 The center line of a plate longitudinal stiffener or the gage line of an angle longitudinal stiffener shall be D/5 from the inner surface or leg of the compression flange component. The longitudinal stiffener shall be proportioned so that:

(10-33)

where: I

=

D t,,.

= =

10.34.4.7

10.34.5.2

b’

~b

2,250

(10-34)

where: width of stiffeners; =

calculated compressive bending stress in the flange.

10.34.5.3 The stress in the stiffener shall not be greater than the basic allowable bending stress for the material used in the stiffener. 10.34.5.4 Longitudinal stiffeners are usually placed on one side only of the web plate. They need not be continuous and may be cut at their intersections with the transverse stiffeners.

10.34.5.5 For longitudinally stiffened girders, transverse stiffeners shall be spaced a distance, dr,, according to shear capacity as specified in Article 10.34.4.2, but not more than 1.5 times the maximum subpanel depth. The handling requirement given in Article 10.34.4.2 shall not apply to longitudinally stiffened girders. The spacing of the first transverse stiffener at the simple support end of a longitudinally stiffened girder shall be such that the shearing stress in the end panel does not exceed the value given in Article 10.34.4.3. The maximum spacing of the first transverse stiffener at the simple support end of a longitudinally stiffened girder is limited to 1.5 times the maxmmum subpanel depth. The total web depth D shall be used in determining the shear capacity of longitudinally stiffened girders in Articles 10.34.4.2 and 10.34.4.3. 10.34.5.6 Transverse stiffeners for girder panels with longitudinal stiffeners shall be designed according to Article 10.34.4.7 except that the maximum subpanel depth shall be used instead of the total panel depth, D.

10.34.6 Bearing Stiffeners 10.34.6.1

mtnimnum moment of inertia of the longitudinal stiffener about its edge in contact with the web 4; plate in inches unsupported distance between flange components in inches; thickness of the web plate in inches; actual distance between transverse stiffeners in inches.

The thickness of the longitudinal stiffener

t, shall not be less than:

Welded Girders

Over the end bearings of welded plate girders amid over the intermediate bearings of continuous welded plate girders there shall be stiffeners. They shall extend as nearly as practicable to the outer edges of the flange plates. They preferably shall be made of plates placed on both sides of the web plate. Bearing stiffeners shall be designed as columns, and their connection to the

web shall be designed to transmit the entire end reaction to the bearings. For stiffeners consisting of two plates, the column section shall be assumed to comprise the two plates and a centrally located strip of the web plate whose width is equal to not more than 18 times its thickness. For stiffeners consisting of four or more plates, the column section shall be assumed to comprise the four or more plates and a centrally located strip of the web plate whose width is equal to that enclosed by the four or more plates plus a width of not more than 18 times the web plate thickness. (See Article 10.40 for Hybrid Girders.) The radius of gyration shall be computed about the axis through the center line of the web plate. The stiffeners shall be ground to fit against the flange through which they receive their reaction, or attached to the flange by full penetration groove welds. Only the portions of the stiffeners outside the flangeto-web plate welds shall be considered effective in bearing. The thickness of the bearing stiffener plates shall not be less than,

10.35

TRUSSES

10.35.1

member plus any other external force. For compression members, an additional force shall be added as obtained by the following formula: V~PF 100 + (L/r)F~ 100 [jir +10 3,300,0001

V

=

P

=

=

(10-35)

The allowable compressive stress and the bearing pressure

1

(10-37)

In the above expression:

r

1Y ‘133,000

Perforated Cover Plates and Lacing Bars

The shearing force normal to the member in the planes of lacing or continuous perforated plates shall be assumed divided equally between all such parallel planes. The shearing force shall include that due to the weight of the

=

=

on the stiffeners shall not exceed the values specified in Article 10.32.

10.35.2 10.34.6.2

261

DIVISION I—DESIGN

10.34.6.1

normal shearing force in pounds; allowable compressive axial load on members in pounds; length of member in inches; radius of gyration of section about the axis perpendicular to plane of lacing or perforated plate in inches; specified minimum yield point of type of steel being used.

Compression Members—Thickness of Metal

Riveted or Bolted Girders 10.35.2.1

Over the end bearings of riveted or bolted plate girders there shall be stiffener angles, the outstanding legs of which shall extend as nearly as practicable to the outer edge on the flange angle. Bearing stiffener angles shall be proportioned for bearing on the outstanding legs of flange angles, no allowance being made for the portions of the legs being fitted to the fillets of the flange angles.

Compression members shall be so designed

that the main elements of the section will be connected directly to the gusset plates, pins, or other members.

10.35.2.2 The center of gravity of a built-up section shall coincide as nearly as practicable with the center of the section. Preferably, segments shall be connected by solid webs or perforated cover plates.

Bearing stiffeners shall be arranged, and their connections to the web shall be designed to transmit the entire end reaction to the bearings. They shall not be crimped. The thickness of the bearing stiffener angles shall not be less than:

V

F~

12

33,000

10.35.2.3 Plates supported on one side, outstanding legs of angles and perforated plates—for outstanding

plates, outstanding legs of angles, and perforated plates at the perforations, the b/t ratio of the plates or angle segments when used in compression shall not be greater than the value obtained by use of the formula:

(10-36) b

1,625

(10-38)

~ The allowable compressive stress and the bearing pressure on the stiffeners shall not exceed the values specified in Article 10.32.

but in no case shall bit be greater than 12 for main memhers and 16 for secondary members.

HIGHWAY BRIDGES

262

(Note: b is the distance from the edge of plate or edge of perforation to the point of support.) 10.35.2.4

When the compressive stress equals the

limiting factor of 0.44 F~, the b/t ratio of the segments indicated above shall not be greater than the ratios shown for the following grades of steel: psi, Y.P. Mm. 50,000 psi, Y.P. Mm. 70,000 psi, Y.P. Mm. 90,000 psi, YR Mm. 100,000 psi, YP. Mm. 36,000

b/t b/t b/t b/t b/t

II

=

9

=

8

=

7.5

4,000

When the compressive stresses equal the

limiting factor of 0.44 F,, the b/t ratio of the plates and segments indicated above shall not be greater than the ratios shown for the following grades of steel: 36,000 psi, Y.P. Mm. bit

= 32

50,000 psi, Y.P. Mm, b/t 70,000 psi, Y.P. Mm. b/t

= 27

psi. Y.P. Mm. b/t 100,000 psi, Y.P. Mm. bit 90,000

10.35.2.8 When the compressive stresses equal the limiting factor of 0.44 F:,, the b/t ratio of the cover plate and webs indicated above shall not be greater than the ra-

tios shown for the following grades of steel: 36,000 psi, Y.P. Mm. b/t 50,000 psi, Y.P. Mm. b/t

= 40

psi, Y.P. Mm. b/t 90,000 psi, Y.P. Mm. b/t 100,000 psi, Y.P. Mm. b/t

= 28 = 25 = 24

use of the formula: b

6,000

~

fa

shall be satisfied.)

10.35.2.10 When the compressive stresses equal the limiting factor of 0.44 F:,, the b/t ratio of the perforated cover plates shall not be greater than the ratios shown for the following grades of steel:

= 23

36,000 psi, YP. Mm. b/t

= 48

= 20

50,000

psi, Y.P. Mm. b/t

= 41

= 19

70,000 psi, Y.P. Mm. bit

= 34

psi, YP. Mm. b/t psi, Y.P. Mm. b/t

= 30

Solid cover plates supported on two edges

(10-41)

but in no case shall bit be greater than 55. (Note: b is the distance between points of support. Attention is directed to requirements for plate thickness at perforations, namely, plate supported on one side, which also

90,000

10.35.2.7

= 34

10.35.2.9 Perforated cover plates supported on two edges—for members of box shapes consisting of perforated cover plates connecting main plates or segments, the b/t ratio of the perforated cover plates when used in compression shall not be greater than the value obtained by

(10-39)

but in no case shall b/t be greater than 45. (Note: b is the distance between points of support for the plate and between roots of flanges for the webs of rolled segments.) 10.35.2.6

support.)

70,000

10.35.2.5 Plates supported on two edges or webs of main component segments—for members of box shape consmsting of main plates, rolled sections, or made up component segments with cover plates, the b/t ratio of the main plates or webs of the segments when used in compression shall not be greater than the value obtained by use of the formula: b

(Note: b is the unsupported distance between points of

= 12 =

10.35.2.3

100,000

= 29

or webs connecting main members or segments—for

members of H or box shapes consisting of solid cover

In the above expressmons—

plates or solid webs connecting main plates or segments,

the bit ratio of the solid cover plates or webs when used in compression shall not be greater than the value obtained by use of the formula: b

7-

=

b

=

=

5,000 \/~f~

but in no case shall b/t be greater than 50.

(10-40)

computed compressive stress;

width (defined as indicated for each expression); plate or web thickness.

10.35.2.11

The point of support shall be the inner line of fasteners or fillet welds connecting the plate to the main segment. For plates butt welded to the flange edge of rolled segments the point of support may be taken as the

10.35.2.11

263

DIVISION I—DESIGN

weld whenever the ratio of outstanding flange width to flange thickness of the rolled segment is less than seven. Otherwise, point of support shall be the root of flange of rolled segment. Terminations of the butt welds are to be ground smooth.

10.37

SOLID RIB ARCHES

10.37.1

Moment Amplification and Allowable Stress

10.37.1.1 Live load plus impact moments that are determined by an analysis which neglects arch rib deflection

shall be increased by an amplification factor A~: 10.36

COMBINED STRESSES AF

All members subjected to both axial compression and bending stresses shall be proportioned to satisfy the following requirements: F, F,

5.

+

Cii,yf~,y

(1 —~$-.)F~.

(1—

S

1.0

(10-45)

______ 1 70T I—

AFe

where: T

Cmxf

—

=

=

(10-42)

arch rib thrust at the quarter point from dead plus live plus impact loading;

~~FbY

(Euler buckling stress)

=

(~~2

one-half of the length of the arch rib; area of cross section;

(10-46)

and: + ~b5

=1.0 (at points of support)

~

FbX

FbY

(10-43)

L

=

A

=

r K

= =

radius of gyration; factor to account for effective length. K Values for Use in Calculating F~ and F,

where: 2 C

2

(10-44)

Rise to Span

3-Hinged

Ratio

Arch

itE F.S. (KbLb/rb)

0.2—0.3

1.16 1.13

0.3-0.4

1.16

0.1—0.2 =

computed axial stress;

or f 5:,

=

computed compressive bending stress about the x axis and y axis, respectively;

F,

=

axial stress that would be permitted if axial force alone existed, regardless of the plane

F,,~. F,,:,

=

k+

compressive bending stress that would be

F5

=

l0.32.IA;

E

=

Kh

=

=

rh

=

Cmx, Ce,:,

=

ES.

=

Euler buckling stress divided by a factor of safety;

modulus of elasticity of steel; effective length factor in the plane of bending (see Appendix C); actual unbraced length in the plane of bending; radius of gyration in the plane of bending; coefficient about the x axis and y axis, respectively, whose value is taken from Table l0.36A; factor of safety = 2.12.

0.70 0.70 0.72



(10-66)

4):

2

5

i’:

as equal to 10,000 psi); =

allowable range of horizontal shear on an individual shear connector.

The additional connectors, N~, shall be placed adjacent to the point of dead load contraflexure within a distance

equal to one-third the effective slab width, i.e., placed either side of this point or centered about it. It is preferable to locate field splices so that they clear the connectors. 10.38.5.2 Vertical Shear The intensity of unit-shearing stress in a composite

t7E~

(10-67)

5=0.4d

where:

modulus of elasticity of the concrete in pounds

=

range of stress due to live load plus impact in the slab reinforcement over the support (in lieu of more accurate computations, f, may be taken

specified minimum yield point of the reinforcing steel.

The ultimate strength of the shear connector is given as follows:

10.38.5.1.2

girder may be determined on the basis that the web of the steel girder carries the total external shear, neglecting the effects of the steel flanges and of the concrete slab. The shear may be assumed to be uniformly distributed throughout the gross area of the web.

per square inch;

10.38.6 E~ ~w31233

f~’

S.

=

h

=

ultimate strength of individual shear connector in average flange thickness of the channel flange in

= =

inches; thickness of the web of a channel in inches; length of a channel shear connector in inches;

=

compressive strength of the concrete in 28 days

pounds;

W

in pounds per square inch; d

=

diameter of stud in inches;

w

=

unit weight of concrete in pounds per cubic foot.

10.38.5.1.3

Additional Connectors to Develop Slab Stresses

The number of additional connectors required at points of contraflexure when reinforcing steel embedded in the concrete is not used in computing section properties for negative moments shall be computed by the formula: =

A~fr/Zr

(10-69)

where: =

number of additional connectors for each beam

at point of contraflexure; Ax

=

Deflection

(10-68)

total area of longitudinal slab reinforcing steel for each beam over interior support;

vWhen reinforcement steel embedded in the top slab is not used in computing section properties for negative moments, P is equal to zero.

10.38.6.1 The provisions of Article 10.6 in regard to deflections from live load plus impact also shall be applicable to composite girders. 10.38.6.2 When the girders are not provided with falsework or other effective intermediate support during the placing of the concrete slab, the deflection due to the weight of the slab and other permanent dead loads added before the concrete has attained 75 percent of its required 28-day strength shall be computed on the basis of noncomposite action. 10.39

10.39.1

COMPOSITE BOX GIRDERS

General

10.39.1.1 This section pertains to the design of simple and continuous bridges of moderate length supported by two or more single cell composite box girders. The distance center-to-center of flanges of each box should be the same and the average distance center-to-center of flanges of adjacent boxes shall be not greater than 1 .2 times and not less than 0.8 times the distance center-to-center of flanges of each box. In addition to the above, when nonpa-

rallel girders are used, the distance center-to-center of adjacent flanges at supports shall be not greater than 1 .35 times and not less than 0.65 times the distance center-tocenter of flanges of each box. The cantilever overhang of the deck slab, including curbs and parapets, shall be limited to 60 percent of the average distance center-to-center

DIVISION I—DESIGN

10.39. 1.1

of flanges of adjacent boxes, but shall in no case exceed 6 feet. 10.39.1.2 The provisions of Division I, Design, shall govern where applicable, except as specifically modified by Articles 10.39.1 through 10.39.8.

10.39.2

Lateral Distribution of Loads for Bending Moment

10.39.2.1

The live load bending moment for each box girder shall be determined by applying to the girder, the fraction WL of a wheel load (both front and rear), determined by the following equation:

Wt=0.l+l.7R+

0.85

269

to 4, and the width of the bottom flange is no greater than 20 percent of the span, then the transverse bending stresses resulting from distortion of the span, and the

transverse bending stresses resulting from distortion of the girder cross section and from vibrations of the bottom plate need not be considered. For structures in this category transverse bending stresses due to supplementary loadings, such as utilities, shall not exceed 5,000 psi. 10.39.3.2.2 For structures exceeding these limits, a detailed evaluation of the transverse bending stresses due to all causes shall be made. These stresses shall be limited to a maximum stress or range of stress of 20,000 psi. 10.39.4

Design of Bottom Flange Plates

(10-70)

10.39.4.1 where,

Number of Box Girders N0

(10-71)

=

W~/l2 reduced to the nearest whole number;

=

roadway width between curbs in feet, or barriers if curbs are not used. R shall not be less than 0.5 or greater than 1.5.

10.39.2.2 The provision of Article 3.12, Reduction of Load Intensity, shall not apply in the design of box girders when using the design load WL given by the above equation. 10.39.3

Design of Web Plates

10.39.3.1

Vertical Shear

Tension Flanges

10.39.4.1.1 In cases of simply supported spans, the bottom flange shall be considered completely effective in resisting bending if its width does not exceed one-fifth the span length. If the flange plate width exceeds one-fifth of the span, an amount equal to one-fifth of the span only shall be considered effective. 10.39.4.1.2 For continuous spans, the criteria above shall be applied to the lengths between points of contraflexure.

10.39.4.2

Compression Flanges Unstiffened

10.39.4.2.1 Unstiffened compression flanges designed for the basic allowable stress of 0.5SF:, shall have a width to thickness ratio equal to or less than the value obtained by the use of the formula: b

The design shear V for a web shall be calculated using the following equation: V0

=

V~/cos 0

(10-72)

= =

= =

vertical shear; angle of inclination of the web plate to the vertical.

10.39.3.2 Secondary Bending Stresses 10.39.3.2.1 Web plates may be plumb (900 to bottom of flange) or inclined. If the inclination of the web plates to a plane normal to the bottom flange is no greater than I

6,140

(10-73)

Fy

where: b

where: 0

t~

flange width between webs in inches; flange thickness in inches.

10.39.4.2.2 For greater b/t ratios, but not exceeding 60, the stress in an unstiffened bottom flange shall not exceed the value determined by the use of the formula: =

0.5SF:,

—

0.224F~x

F:

(10-74)

10.39.4.2

HIGHWAY BRIDGES

270 100

REQUIRED

70 Fcr

~y tb

=

0.55 F~

Fcr

0.g6 F~, tb

Fer

0.85 Fy, ~b 0.47 F~

t4~

6.140

0.53 Fy, b

T

b,,.F.

8,200 -

10060

60 NOTE: Fcr refers to Load Factor Design lb refers to 2Working StressDesign

F

5

iS in lb/in

Is

40

10

10000

15000

FIGURE l0.39.4.3A.

20000

25000

30000

Longitudinal Stiffeners—Box Girder Compression Flange

10.39.4.2

DIVISION I—DESIGN

271

0.07

3

0.06

0.04 a

It E B?AfF~ 1.5

0.03

0.5

FIGURE l0.39.43B. Spacing and Size of Transverse StitTenem’s (for Flange Stiffened Longitudinally and Transversely)

HIGHWAY BRIDGES

272

10.39.4.2.3 For values of b/t exceeding I 3,300/\/~, the stress in the flange shall not exceed the value given by the formula:

0.5SF:, — 0.224F:, x

=

6,650V~— w [l~

=

10.39.4.2.4

57.6(!j~ x 106

10.39.4.2.3

stn

ceed 60 except in areas of low stress near points of dead load contraflexure.

Compression Flanges Stiffened Longitudinally*

10.39.4.3.1 Longitudinal stiffeners shall be at equal spacings across the flange width and shall be proportioned

so that the moment of inertia of each stiffener about an axms parallel to the flange and at the base of the stiffener is at least equal to: I,

=

4

t~w

(10-76)

3n4 for values of n greater than I; = 0.07 k ~ =O.l25k3foravalueofn= I; tf = thickness of the flange; w = width of flange between longitudinal stiffeners or distance from a web to the nearest longitudinal stiffener; n = number of longitudinal stiffeners; k = buckling coefficient which shall not exceed 4. 10.39.4.3.2 For the flange, including stiffeners, to be designed for the basic allowable stress of 0.55 F:,, the ratio w/t shall not exceed the value given by the formula:

3,0701k

F>,

=

X

l0~

(10-79)

10.39.4.3.6 If the longitudinal stiffeners are placed at their maximum w/t ratio to be designed for the basic al-

lowable design stresses of 0.55 F>. and the number of longitudinal stiffeners exceeds 2, then transverse stiffeners should be considered. Compression Flanges Stiffened Longitudinally and Transversely

10.39.4.4.1

The longitudinal stiffeners shall be at equal spacings across the flange width and shall be proportioned so that the moment of inertia of each stiffener

about an axis parallel to the flange and at the base of the stiffener is at least equal to: I,

=

8 t~w

(10-80)

10.39.4.4.2 The transverse stiffeners shall be proportioned so that the moment of inertia of each stiffener about an axis through the centroid of the section and parallel to its bottom edge is at least equal to: =0.l0(n+I)3 3f Af Ea

(10-81)

where: Af

=

a

=

area of bottom flange including longitudinal

stiffeners; =

in solving these equations a value of k between 2 and 4 generally should be assumed.

14.4 k(t/w)2

1 0.39.4.3.5 When longitudinal stiffeners are used, it ms preferable to have at least one transverse stiffener placed near the point of dead load contraflexure. The stiffener should have a size equal to that of a longitudinal stiffener.

(10-77)

10.39.4.3.3 For greater values of w/t but not exceeding 60 or (6,650 Vi~)/ F:,, whichever is less, the stress in the flange, including stiffeners, shall not exceed the value determined by the formula:

(I 0—78)

formula:

10.39.4.4

where:

NiII

10.39.4.3.4 For values of w/t exceeding (6,650 k)/ F:, but not exceeding 60, the stress in the flange, including stiffeners, shall not exceed the value given by the

10.39.4.2.5 Should the b/t ratio exceed 45, longitudinal stiffeners should be considered.

10.39.4.3

Fy

3,580 \/j~

(10-75)

The b/t ratio preferably should not ex-

t

E

=

spacing of transverse stiffeners;

maximum longitudinal bending stress in the flange of the panels on either side of the transverse stiffener; modulus of elasticity of steel.

273

DIVISION I—DESIGN

10.39.4.4.3

10.39.4.4.3 For the flange, including stiffeners, to be designed for the basic allowable stress of 0.55 F:,, the ratio w/t for the longitudinal stiffeners shall not exceed the

10.39.4.4.8 The connection to each longitudinal stiffener shall be designed to resist the vertical force determined by the formula:

value given by the formula: w

FS ys nb

3,070 k

1

(10-87)

(10-82)

F>

10.39.4.5

Compression Flange Stiffeners, General

where: 10.39.4.5.1 The width to thickness ratio of any outstanding element of the flange stiffeners shall not exceed 2’~

(n +1)] [l+(a/b) 2[l ] +0.1 +87.3

(n + l)¾a/ b)

(10-83)

the value determined by the formula:

10.39.4.4.4 For greater values of w/t, but not exceeding 60 or (6,650 k,)/ F:,, whichever is less, the stress in the flange, including stiffeners, shall not exceed

the value determined by the formula: 0.5SF:,

[ 1

0.224F:, x

—

=

(

w

smn1~’X 6,650

10.39.4.4.5

k — 3,580 v’~7

2,600

t’

F>,

(10-88)

where: =

=

b’

Fy

F:,

Ni

/1

(10-84)

For values of w/t exceeding (6,650

k,)/\/~ but not exceeding 60, the stress in the flange, including stiffeners, shall not exceed the value given by the formula:

=

width of any outstanding stiffener element thickness of outstanding stiffener element yield strength of outstanding stiffener element.

10.39.4.5.2 Longitudinal stiffeners shall be extended to locations where the maximum stress in the flange does

not exceed that allowed for base metal adjacent to or connected by fillet welds. 10.39.5 Design of Flange to Web Welds The total effective thickness of the web-flange welds

shall be not less than the thickness of the web, except, =

when two or more interior intermediate diaphragms per

l4.4k 1(±~ x 106

(10- 85)

10.39.4.4.6 The maximum value of the buckling coefficient, k,, shall be 4. When k, has its maximum value, the transverse stiffeners shall have a spacing, a, equal to or less than 4w. If the ratio a/b exceeds 3, transverse stiffeners are not necessary. 10.39.4.4.7 The transverse stiffeners need not be connected to the flange plate but shall be connected to the

webs of the box and to each longitudinal stiffener. The connection to the web shall be designed to resist the vertical force determined by the formula: FS =

where 5,

=

ys

(10-86)

span are provided, the minimum size fillet welds specitied in Article 10.23.2.2 may be used. Regardless of the type weld used, welds shall be deposited on both sides of the

connecting flange or web plate. 10.39.6

Diaphragms

10.39.6.1

Diaphragms, cross-frames, or other means

shall be provided within the box girders at each support to resist transverse rotation, displacement, and distortion. 10.39.6.2 Intermediate diaphragms or cross-frames are not required for steel box girder bridges designed in

accordance with this specification. 10.39.7

Lateral Bracing

2b

seetton modulus of the transverse stiffener.

Generally, no lateral bracing system is required between box girders. A horizontal wind load of 50 pounds

274

per square foot shall be applied to the area of the superstructure exposed in elevation. Half of the resulting force

shall be applied in the plane of the bottom flange. The section assumed to resist the horizontal load shall consist of the bottom flange acting as a web and 12 times the thickness of the webs acting as flanges. A lateral bracing system shall be provided if the combined stresses due to the specified horizontal force and dead load of steel and deck exceed 1 50 percent of the allowable design stress.

100 = 0.50

C C) 0 4)

95 00

a

90 0 IC .~

Lh~

10.39.8

10.39.7

HIGHWAY BRIDGES

85

z

Access and Drainage

00 = 0.72

0 ‘-

Consistent with climate, location, and materials, consideration shall be given to the providing of manholes, or other openings, either in the deck slab or in the steel box

80

C) 0

w

75

for form removal, inspection, maintenance, drainage, etc. 70 1.0

10.40 10.40.1

HYBRID GIRDERS

1.5

2.0

3.0

3.5

4.0

RATIO OF WEB AREA TO TENSION FLANGE AREA,~

General

FIGURE l0.40.2.lA

10.40.1.1 This section pertains to the design of girders that utilize a lower strength steel in the web than in one or both of the flanges. It applies to compostle and noncomposite plate girders, and composite box girders. At any cross section where the bending stress in either flange exceeds 55 percent of the minimum specified yield strength of the web steel, the compression-tiange area shall not be less than the tension-

flange area. The top-flange area shall include the transformed area of any portion of the slab or reinforcing

steel that is considered to act compositely with the steel girder. 10.40.1.2 The provisions of Division I, Design, shall govern where applicable, except as specifically modified by Articles 10.40.1 through 10.40.4.

100

C)

C)

C) a

0 I0

U-

z 0 0 0

w

10.40.2 Allowable Stresses 1.0

Bending

10.40.2.1

2.5

1.

RATIO OF WEB

AREA

3.5 TO TENSION FLANGE AREA,

P

FIGURE I0.40.2.lB

10.40.2.1.1

The bending stress in the web may ex-

ceed the allowable stress for the web steel provided that the stress in each flange does not exceed the allowable stress from Articles 10.3 or 10.32 the steel in that

for

where:

a

=

vided by the minimum specified yield strength of

flange multiplied by the reduction factor, R.

the tension flange;* 13

Fl

=

2 (3 I — 1¾’ (1 - a)

i~, +

mtnimum specified yield strength of the web di-

(10-89)

(See Figure 10.40.2.1 A and 10.40.2.1 B.)

=

area of the web divided by the area of the tension

flange;* 0)Bottom flange oforthotropic deck bridges.

10.40.2.1.1

4*

=

DIVISION I—DESIGN

275

distance from the outer edge of the tension flange* to the neutral axis (of the transformed

ally the deck plate is stiffened by longitudinal ribs and transverse beams; effective widths of deck plate act as the

section for composite girders) divided by the

top flanges of these ribs and beams. Usually the deck including longitudinal ribs, acts as the top flange of the main box or plate girders. As used in Articles 10.41.1 through

depth of the steel section. 10.40.2.1.2

The bending stress in the concrete slab in

composite girders shall not exceed the allowable stress for the concrete multiplied by R.

10.41.4.10, the terms rib and beam refer to sections that include an effective width of deck plate. 10.41.1.2

10.40.2.2

The provisions of Division I, Design, shall

govern where applicable, except as specifically tnodified

Shear

by Articles 10.41.1 through 10.41.4.10. The design of the web for a hybrid girder shall be in compliance with specification Article 10.34.3 except that Equation (10-27) of Article 10.34.4.2 for the allowable average shear stress in the web of transversely stiffened non-hybrid girders shall be replaced by the following

equation for the allowable average shear stress in the web of transversely stiffened hybrid girders: =

CF:,/3 ~ F:,/3

(10-90)

The provisions of Article 10.34.4.4, and the equation for A in Article 10.34.4.7 are not applicable to hybrid

girders. 10.40.2.3 Fatigue

An appropriate method of elastic analysis, such as the equivalent-orthotropic-slab method or the equivalent-grid method, shall be used in designing the deck. The equivalent stiffness properties shall be selected to correctly simulate the actual deck. An appropriate method of elastic analysis, such as the thin-walled-beam method, that accounts for the effects of torsional distortions of the crosssectional shape shall be used in designing the girders of orthotropic-deck box-girder bridges. The box-girder design

shall be checked for lane or truck loading arrangements that produce maximum distortional (torsional) effects. 10.41.1.3 For an alternate design method (Strength Design), see Article 10.60. 10.41.2

Hybrid girders shall be designed for the allowable fatigue stress range given in Article 10.3, Table 10.3.1 A. 10.40.3

Plate Thickness Requirements

Wheel Load Contact Area

The wheel loads specified in Article 3.7 shall be uniformly distributed to the deck plate over the rectangular area defined below:

In calculating the maximum width-to-thickness ratto of the flange plate according to Article 10.34.2 and the minimum thickness of the web plate according to Article 10.34.3, f,, shall be taken as the calculated bending stress in the compression flange divided by the reduction factor, R. 10.40.4

Bearing Stiffener Requirements

In designing bearing stiffeners at interior supports of continuous hybrid girders for which c~ is less than 0.7, no part of the web shall be assumed to act in bearing. 10.41

10.41.1

ORTHOTROPIC-DECK SUPERSTRUCTURES

General

10.41.1.1 This section pertains to the design of steel bridges that utilize a stiffened steel plate as a deck. Usu5Bottom Ilange oforthotropic dock bridges.

Wheel Load (kip) 8 12 16

Width Perpendicular

Length in Direction

to Traffic (inches) of Traffic (inches) 20 + 2t 20 + 2t 24 ±2t

8 + 2t 8 + 2t 8 + 2t

In the above table, t is the thickness of the wearing surface in inches. 10.4 1.3

Effective Width of Deck Plate

10.41.3.1

Ribs and Beams

The effective width of deck plate acting as the top

flange of a longitudinal rib or a transverse beam may be calculated by accepted approximate methods.*

*Design Manual for ~Orthotropic Steel Plate Deck Bridges,’ AISC, 1963, or Orthotropic Bridges, Theory and Design,’ by MS. Troitsky. Lincoln Arc Welding Foundation, 1967.

HIGHWAY BRIDGES

276

10.41.3.2 Girders 10.4 1.3.2. 1 The full width of deck plate may be considered effective in acting as the top flange of the girders if the effective span of the girders is not less than: (1) 5 times the maximum distance between girder webs and (2)

10 times the maximum distance from edge of the deck to the nearest girder web. The effective span shall be taken as the actual span for simple spans and the distance between points of contraflexure for continuous spans. Alternatively, the effective width may be determined by ac-

cepted analytical methods. 10.41.3.2.2 The effective width of the bottom flange of a box girder shall be determined according to the pro-

visions of Article 10.39.4.1. 10.41.4 Allowable Stresses 10.41.4.1

Local Bending Stresses in Deck Plate

The term local bending stresses refers to the stresses caused in the deck plate as it carries a wheel load to the ribs and beams. The local transverse bending stresses caused in the deck plate by the specified wheel load plus 30-percent impact shall not exceed 30,000 psi unless a higher allowable stress is justified by a detailed fatigue analysis or by applicable fatigue-test results. For deck configurations in which the spacing of transverse beams is at least 3 times the spacing of longitudinal-rib webs, the local longitudinal and transverse bending stresses in the deck plate need not be combined with the other bending stresses covered in Articles 10.41.4.2 and 10.41.4.3. 10.41.4.2

Bending Stresses in Longitudinal Ribs

The total bending stresses in longitudinal ribs due to a combination of (I) bending of the rib and (2) bending of the girders may exceed the allowable bending stresses in Article 10.32 by 25 percent. The bending stress due to each of the two individual modes shall not exceed the allowable bending stresses in Article 10.32.

10.41.3.2

connections of beams to the webs of girders, and rib splices may affect the fatigue life of the bridge when they occur in regions of tensile stress. Where applicable, the number of cycles of maximum stress and the allowable fatigue stresses given in Article 10.3 shall be applied in designing these details; elsewhere, a rational fatigue analysis shall be made in designing the details. Connections

between webs of longitudinal ribs and the deck plate shall be designed to sustain the transverse bending fatigue stresses caused in the webs by wheel loads. 10.4 1.4.5

Thickness of Plate Elements

10.41.4.5.1

Longitudinal Ribs and Deck Plate

Plate elements comprising longitudinal ribs, and deck-plate elements between webs of these ribs, shall meet the minimum thickness requirements of Article 10.35.2. The quantity f.~ may be taken as 75 percent of the sum of the compressive stresses due to (I) bending of the rib and (2) bending of the girder, but not less than the compressive stress due to either of these two individual bending modes. 10.41.4.5.2

Girders and Transverse Beams

Plate elements of box girders, plate girders, and transverse beams shall meet the requirements of Articles 10.34.2 to 10.34.6 and 10.39.4. 10.41.4.6

Maximum Slenderness of Longitudinal Ribs

The slenderness, L/r, of a longitudinal rib shall not exceed the value given by the following formula unless it can be shown by a detailed analysis that overall buckling of the deck will not occur as a result of compressive stress induced by bending of the girders: (L~

=

1,000

1,500 F>,

—

2,700F .,

(10-91)

where: 10.41.4.3

Bending Stresses in Transverse Beams

The bending stresses in transverse beams shall not exceed the allowable bending stresses in Article 10.32. 10.41.4.4

Intersections of Ribs, Beams, and Girders

Connections between ribs and the webs of beams, holes in the webs of beams to permit passage of ribs,

distance between transverse beams; radius of gyration about the horizontal centroidal axis of the rib including an effective width of

L

=

r

=

F

=

deck plate; maximum compressive stress in psi in the deck

=

plate as a result of the deck acting as the top flange of the girders; this stress shall be taken as positive; yield strength of rib material in psi.

F:,

DIVISION I—DESIGN

10.41.4.7 10.41.4.7

Diaphragms

10.41.4.8.2

Diaphragms, cross frames, or other means shall be

provided at each support to transmit lateral forces to the bearings and to resist transverse rotation, displacement, and distortion. Intermediate diaphragms or cross frames shall be provided at locations consistent with the analysis of the girders. The stiffness and strength of the intermediate and support diaphragms or cross frames shall be consistent with the analysis of the girders. 10.41.4.8

Stiffness Requirements

10.41.4.8.1

277

Deflections

The deflections of ribs, beams, and girders due to live load plus impact may exceed the limitations in Article 10.6 but preferably shall not exceed ‘tss:, of their span. The calculation of the deflections shall be consistent with the analysis used to calculate the stresses. To prevent excessive deterioration of the wearing surface, the deflection of the deck plate due to the specified wheel load plus 30-percent impact preferably shall be less than ‘/MX of the distance between webs of ribs. The stiffening effect of the wearing surface shall not be included in calculating the deflection of the deck plate.

Vibrations

The vibrational characteristics of the bridge shall be considered in arriving at a proper design. 10.4 1.4.9

Wearing Surface

A suitable wearing surface shall be adequately bonded to the top of the deck plate to provide a smooth, nonskid riding surface and to protect the top of the plate against corrosion and abrasion. The wearing surface material shall

provide (1) sufficient ductility to accommodate, without cracking or debonding, expansion and contraction imposed by the deck plate, (2) sufficient fatigue strength to withstand flexural cracking due to deck-plate deflections, (3) sufficient durability to resist rutting, shoving, and wearing, (4) imperviousness to water and motor-vehicle fuels and oils, and (5) resistance to deterioration from deicing salts, oils, gasolines, diesel fuels, and kerosenes. 10.41.4.10

Closed Ribs

Closed ribs without access holes for inspection, clean-

ing, and painting are permitted. Such ribs shall be sealed against the entrance of moisture by continuously welding (1) the rib webs to the deck plate, (2) splices in the ribs, and (3) diaphragms, or transverse beam webs, to the ends of the ribs.

Part D STRENGTH DESIGN METHOD

LOAD FACTOR DESIGN 10.42

SCOPE

Load factor design is a method of proportioning structural members for multiples of the design loads. To ensure serviceability and durability, consideration is given to the control of permanent deformations under overloads, to the fatigue characteristics under service loadings, and to the control of live load deflections under service loadings. See

10.43.3 Overloads are the live loads that can be allowed on a structure on infrequent occasions without causing

permanent damage. For design purposes, the maximum overload is taken as 5(L + 1)/3. 10.43.4

The maximum loads are the loadings specified

in Article 10.47.

Part C—Service Load Design Method—Allowable Stress

Design for an alternate design procedure.

10.44

10.43

10.44.1 The moments, shears, and other forces shall be determined by assuming elastic behavior of the structure

LOADS

DESIGN THEORY

except as modified in Article 10.48.1.3. Service live loads are vehicles which may operate on a highway legally without special load permit. 10.43.1

10.43.2 For design purposes, the service loads are taken as the dead, live, and impact loadings described in Section 3.

The members shall be proportioned by the methods specified in Articles 10.48 through 10.56 so that 10.44.2

their computed maximum strengths shall be at least equal to the total effects of design loads multiplied by their re-

spective load factors specified in Article 3.22.

278

HIGHWAY BRIDGES

10.44.3 Service behavior shall be investigated as specifled in Articles 10.57 through 10.59.

10.44.3

Rolled or fabricated I-shaped beams and fabricated girders meeting the requirements of Article 10.48.1.1 below shall be considered compact sections and the max-

10.45

ASSUMPTIONS

imum strength shall be as computed: M, =F,Z

10.45.1 Strain in flexural members shall be assumed directly proportional to the distance from the neutral axis. 10.45.2 Stress in steel below the yield strength, F:,, of the grade of steel used shall be taken as 29,000,000 psi times the steel strain. For strain greater than that corresponding to the yield strength, F:,, the stress shall be considered independent of strain and equal to the yield strength, F:,. This assumption shall apply also to the longitudinal reinforcement in the concrete floor slab in the region of negative moment when shear connectors are provided to ensure composite action in this region.

Where F:, is the specified yield point of the steel being used, Z is the plastic section modulus.* 10.48.1.1 Beams and girders designed as compact sections shall meet the following requirements: (For certain frequently used steels these requirements are listed in Table 10.48.1.2A.)

(a) Projecting compression flange element: b’

2,055

10.45.3 At maximum strength the compressive stress in the concrete slab of a composite beam shall be assumed independent of strain and equal to 0.85~’. 10.45.4 Tensile strength of concrete shall be neglected in flexural calculations.

where b’ is the width of the projecting flange element. is the flange thickness. (b) Web thickness: <

DESIGN STRESS FOR STRUCTURAL STEEL

The design stress for structural steel shall be the spec-

ified minimum yield point or yield strength, F:,, of the steel used as set forth in Article 10.2.

(10-93)

F>,

D 10.46

(10-92)

19,230

F>,

(10-94)

where D is the clear distance between the flanges, the web thickness.

t~

ms

When both b’/t and D/t~~ exceed 75% of the above lim-

tts, the following interaction equation shall apply: 10.47

MAXIMUM DESIGN LOADS

The maximum moments, shears, or forces to be sus-

tamed by a stress-carrying member shall be computed for the load combinations specified in Article 3.22. Each part of the structure shall be proportioned for the group loads that are applicable and the maximum design required by the group loading combinations shall be used. 10.48

SYMMETRICAL BEAMS AND GIRDERS

D

(b’~

t 5’

~

(10-95)

where F.

5 is the yield strengfh of the compression flange. (c) Lateral bracing:

Lb

, (psi) b’/t

*

36,000 10.8

50,000 9.2

D/t~

101

86

Lblr:, (MtIM., = 0*) Lb/r:, (Mt/MU = 1*)

100

72

39

28

279

10.48.2 Braced Noncompact Sections For rolled or fabricated I-shaped beams and fabricated girders not meeting the requirements of Article 10.48.1.1 but meeting the requirements of paragraph 10.48.2.1 below, the maximum strength shall be cotnputed as:

For values of MI/M, other than 0 and I, use Equation (10.95). =

F~S

(10-98)

where S is the section modulus. the steel section with respect to the Y-Y axis, M

1 is the smaller moment at the end of the unbraced length of the member, and M, is the ultimate moment from Equation (10-92) at the other end of the unbraced

length: (M1/M5’) is positive when moments cause single curvature between brace points. (MI/MU) is nega-

10.48.2.1 The above equation is applicable to beams and girders meeting the following requirements: (a) Projecting compression flange eletnent: b’

tive when moments cause reverse curvature between brace points. The required lateral bracing shall be provided by braces capable of preventing lateral displacement and twisting of the main members or by embedment of the top and sides of the compression flange in concrete.

t~

Q< ~

(10-97)

where A is the area of the cross section. Members with

axial loads in excess of 0.1SF:,A should be designed as beam-columns as specified in Article 10.54.2. 10.48.1.2 Article 10.48.1 is applicable to steels with stress-strain diagrams that exhibit a yield plateau followed by a strain hardening range. Steels such as AASHTO M 270 Grades 36, 50, and 50W (ASTM A709 Grades 36, 50, and SOW) meet these requiretnents. The limitations set forth in Article 10.48.1 are given in Table 10.48.1 .2A.

F>,

15,400 F~

be reduced by a maximum of 10 percent. Such reduction shall be accompanied by an increase in moments throughout adjacent spans statically equivalent and opposite in sign to the decrease of the negative moments at the adjacent supports. For example, the increase in moment at the center of the span shall equal the average decrease of the moments at the two adjacent supports. The reduction shall not apply to the negative moment of a cantilever.

(10-100)

where D~ is the depth of the web in compression equal D to

-j- for symmetrical girders.

(c) Spacing of lateral bracing for compression flange:

Lb

<

20,000,000A1 F>,d

(10- 101)

where d is the depth of beam or girder, and A, is the flange area. (d) Maximum axial compression: P =0.15 F5A.

10.48.1.3 In the design of a continuous beam of compact section complying with the provision of Articles 10.48. I. 1, negative moments over supports at Overload and Maximum Load determined by elastic analysis may

(10- 99)

where M < MU, b’/t may be increased by the ratio MU/M. (b) Web thickness:

(d) Maximum axial compression:

P =0.15F:,A

2,200

(10-102)

Members with axial loads in excess of 0.15 F:,A should be designed as beam-columns as specified in Article 10.54.2.

10.48.2.2 The limitations set forth in Article 10.48.2.1 above are given in Table l0.48.2.IA. 10.48.2.3

The maximnumn bending strength of mem-

hers not meeting the web requirements of Article 10.48.2.1(b) or the lateral bracing requirements of Article 10.48.2.1(c) shall be computed from the provisions of Article 10.48.4.1.

]

HIGHWAY BRIDGES

280 TABLE 10.48.2.IA

F~ (psi)

36,000

b’/t

11.6

Limitations for Braced Noncompact Sections 50,000

70,000

9.8

8.3

90,000 7.3

100,000 7.0

Lbd

D/tw

10.48.2.3

556

400

286

222

200

162

138

116

103

97

=

12,500 for members with a compression flange area less than the tension flange area.

The moment capacity of the member, Mr, cannot exceed the yield moment, M:,. In addition Mr cannot exceed the lateral torsional buckling moment given below: For members with

stiffened webs: 10.48.3

D

=

—i-

t

X F>,

or with longitudinally

Transitions

The maximum strength of members with geometric properties falling between the limits of Articles 10.48.1 and 10.48.2 may be computed by straight-line interpolation, except that the web thickness must always satisfy Article 10.48.1.1(b). 10.48.4

6Cb

Mr =91 x lO

j0.772~~+

~Y()

~

(10- 103c) 18, 250U

For members with

___

F>,

Unhraced Sections

10.48.4.1 For members not meeting the lateral bracing requirements of Article 10.48.2.1(c), or the web thickness requirements of Article 10.48.2.1(b), and with the ratio of the moment of inertia of the compression flange to the moment of inertia of the member about the vertical axis of the web, 1>11>,, within the limits of 0.1 = 1>11:, 0.9, the maximum strength shall be computed as:

for

Lb=LP

for

L >Lb>LP

=

Lr ~1S72

(l0-103a)

MrRb

CbF>,SXCrl~0.5~Lb

Mr=

<

M,=

\/fTW

for

Lb=Lr

Lb

(l0-103b)

=

1,.

=

A~.

= =

=

X

=

depth of web in compression (in.) = for symmetrical girders; 2 thickness of web (in.); area of compression flange (in.2); lateral torsional buckling moment, or yield moment, defined below (lb-in.); section modulus with respect to compression flange (in.3). Use SUC for live load for a composite section; 15,400 for all members with a compression flange area equal to or greater than the tension flange area;

=Cb F>,S~~

(10- 103g)

unbraced length of the compression flange,

in. L~ =9 ,S00r’/\/’~, inches. = radius of gyration of compression flange

D =

(l0-103e)

(10- 103f)

M~ Rb= 1—0.002 (DcT~ )[D.

L~j

~~O6I>,~d~

I for longitudinally stiffened girders meet-

ing the requirements of Articles 10.48.6 and 10.49.3. For all other members:

(10- 103d)

Mr =M>,

I:,.

=

about the vertical axis in the plane of the web (in.). moment of inertia of compression flange

about the vertical axis in the plane of the web d

= =

(in.4). depth of girder, in. [(bt3). + (bt3), + Dt~>] where b and t repre3

Cb

=

sent the flange width and thickness of the compression and tension flange, respectively (in.4). 1.75 + lOS (M 2 = 2.3 1/M2) + 0.3(MJMj 1 is the smaller and M2 the larger

where M

281

DIVISION I—DESIGN

10.48.4.1

end moment in the unbraced segment of the beam; M11M2 is positive when the moments

width-to-thickness ratio of transverse stiffeners shall be such that:

cause reverse curvature and negative when bent in single curvature. Cb

=

t

1.0 for unbraced cantilevers and for mem-

bers where the moment within a significant portion of the unbraced segment is greater than or equal to the larger of the segment end moments. If the web slenderness DJt~. for the maximum design loads exceeds the upper limit of l8,250/\~~, either the section shall be modified to comply with the limit, or Iongitudinal stiffeners shall be provided. b 10.48.4.2 Members with axial loads in excess of 0.1SF:,A should be designed as beam-columns as specified in Article 10.54.2. 10.48.5

2,600

Transversely Stiffened Girders

10.48.5.1 For girders not meeting the shear requirements of Article 10.48.8.1 (Equation 10-113) transverse stiffeners are required for the web. For girders with transverse stiffeners but without longitudinal stiffeners the thickness of the web shall meet the requirement:

(10- 105)

F>,

where b’ is the projecting width of the stiffener, and F:, is the yield strength of the transverse stiffener. The gross cross-sectional area of intermediate transverse stiffeners shall not be less than: A

=

[0.l5BDt~, (I — C)(V/V~)

—

l8t~jY

(10-106)

whereY is the ratio of web plate yield strength to stiffener plate yield strength; B = 1.0 for stiffener pairs, 1.8 for single angles, and 2.4 for single plates; and C is computed by Article 10.48.8.1. When values computed by Equation (10-106) approach zero or are negative, then transverse stiffeners need only meet the requirements of Equations (10-107), (10-105) and Article 10.34.4.10. The moment of inertia of transverse stiffeners with reference to the midplane of the web shall be not less than: I

=

d0t2J

(10-107)

where:

10.48.5.2 The maximum bending strength of transversely stiffened girders meeting the requirements of Article 10.48.5.1 shall be computed by Articles 10.48.1,

2 2, but not less than 0.5 (10-108) J = 2.5(D/d0) When stiffeners are in pairs, the moment of inertia shall be taken about the center line of the web plate. When single stiffeners are used, the moment of inertia shall be taken about the face in contact with the web plate. Transverse stiffeners need not be in bearing with the tension flange. The distance between the end of the stiffener weld and the near edge of the web-to-flange fillet weld shall not be less than 4t~ or more than 6t~,. Stiffeners provided on only one side of the web must be in bearing against, but need not be attached to, the compression flange for the stiffener to be effective. However, transverse stiffeners which connect diaphragms or crossframes to the beam or girder shall be rigidly connected to both the top and bottom flanges.

10.48.2, or 10.48.4.1, as applicable, subject to the requirements of Article 10.48.8.2.

10.48.6 Longitudinally Stiffened Girders

36,500 t

—

(10-104)

F>,

For different grades of steel this Immit ins: F:,(psi) 192 163 138 122 115

36,000 50,000 70,000 90,000 100,000

10.48.5.3 The shear capacity of transversely stiffened girders shall be computed by Article 10.48.8. The For the use of larger C, values, see Structural Stability Research Council Guide to Stabilit>’ Design Criteriafor Metal Structures. 4th Ed.. pg. 135. ~The upper limit on Q It.. of 18,250/ F, maybe waived for composite girders without longitudinal stiffeners in accordance with Article lt).SOtd) when checking formulas (lO-102d) through (lO-102g) for factored noneomposite dead load only.

10.48.6.1 Longitudinal stiffeners shall be required when the web thickness is less than that specified by Article 10.48.S.1 and shall be placed at a distance D/5 from the inner surface of the compression flange. The web thickness of plate girders with transverse stiffeners and one longitudinal stiffener shall meet the requirement:

)

282

10.48.6.1

HIGHWAY BRIDGES D

10.48.7 Bearing Stiffeners

73,000

(10- 109)

F~

Bearing stiffeners shall be designed for beams and girders as specified in Articles 10.33.2 and 10.34.6.

For different grades of steel, this limit is:

10.48.8

F:,(psi 385 326

36,000 50,000

276

70,000 90,000 100,000

243 231

Shear

10.48.8.1 The shear capacity of rolled or fabricated I-shaped beams and fabricated girders shall be cotnputed as follows: For beams and girders with unstiffened webs, the shear capacity shall be limited to the plastic or buckling shear force as follows:

10.4&6.2 The maximum bending strength of longitudinally stiffened girders meeting the requirements of Article 10.48.6.1 shall be computed by Article 10.48.2 or Article 10.48.4.1 as applicable, subject to the requirement of Article 10.48.8.1. 10.48.6.3 The shear capacity of girders with one longitudinal stiffener shall be computed by Article 10.48.8.1. The dimensions of the longitudinal stiffener shall be such that:

V

=

CV~

(10- 113)

For girders with stiffened webs and (diD) less than or equal to 3, the shear capacity shall be determined by including post-buckling resistance due to tension-field action as follows: (10-114)

087(1—C)j

VU=VP[C+

V~ is equal to the plastic shear force and is determined

(a) the width-to-thickness ratio is not greater than that given by Article 10.48.5.3. (b) the rigidity of the stiffener is not less than:

as follows: (10-115)

V~ =0.58F>,Dt~~

The constant C is equal to the buckling shear stress 1=Dt42.4(~2

~0.l3j

(10-110)

divided by the shear yield stress, and is determined as follows: D

6,000 k ________ F>,

for — t

(c) the radius of gyration of the stiffener is not less than:

C d

0

F

(10—Ill)

23,000

In computing I and r values above, a centrally located web strip not more than l8t~ in width shall be considered as a part of the longitudinal stiffener. Transverse stiffeners for girder panels with longitudinal stiffeners shall be designed according to Article 10.48.5.3 except that the maximum subpanel depth shall be used instead of the total panel depth, D. In addition, the section modulus of the transverse stiffener shall be not less than:

for

6,000

=—(D/d~)S1 3

(10-112)

where D is the total panel depth (clear distance between flange components) and 5, is the section modulus of the longitudinal stiffener at D/5.

1.0 D

F>,

7500

k

t~ 6,00() k

for

C 55

k

=

(10-116)

_ 7,5001k

D

~

x l0~ k

42

(10-117)

F>,

= 5 [5 (d/D)], except k shall be taken as 5 for unstiffened beams and girders.

where the buckling coefficient, k

-t-

->

10.48.8.1

D

F,

DIVISION I—DESIGN

=

clear, unsupported distance between

=

components; distance between transverse stiffeners; yield strength of the web plate.

=

flange

10.48.52 If a girder panel is controlled by equation 10-114 and subjected to simultaneous action of shear and bending moment with the magnitude of the moment higher than 0.75Mg, the shear shall be limited to not more than:

283

10.49.2 Unsymmetrical Sections with Transverse Stiffeners Girders with transverse stiffeners shall be designed and evaluated by the provisions of Article 10.48.5 except that when Q, the clear distance between the neutral axis and the compression flange, exceeds D/2 the web thickness. t~, shall meet the requirement: 18,250

V/Va

=

2.2 — (l.6M/MU)

(10-118)

10.48.8.3 Where transverse intermediate stiffeners are required, transverse stiffeners shall be spaced at a distance, di,, according to shear capacity as specified in Article 10.48.8.1, but not more than 3D. Transverse stiffeners may be omitted in those portions of the girders where the maxmmum shear force is less than the value given by Article 10.48.8.1 (Equation 10-113). subject to the handling requirement below. Transverse stiffeners shall be required if D/t~ is greater than 150. For panels without longitudinal stiffeners, the spacing of these stiffeners shall not exceed D[260/(D/tj]2 to ensure efficient handling, fabrication, and erection of the girders. For longitudinally stiffened girders, transverse stiffeners shall be spaced a distance, d~. according to shear capacity as specified in Article 10.48.8.1, but not more than 1 .5 times the maximum subpanel depth. The handling requirement given above shall not apply to longitudinally stiffened girders. The total web depth D shall be used in determining the shear capacity of longitudinally stiffened girders in Article 10.48.8.1 and in Equation (10-119). The first stiffener space at the simple support end of a transversely or longitudinally stiffened girder shall be such that the shear force in the end panel will not exceed the plastic or buckline shear foree given by the following equation: V

=

CV>,

(10-119)

For transversely stiffened girders. the maximum spacing of the first transverse stiffener is limited to I .SD. For longitudinally stiffened girders, the maximum spacing of the first transverse stiffener is limited to 1 .5 times the maximum subpanel depth. 1049

UNSYMMETRICAL BEAMS AND GIRDERS

F>, 10.49.3

(10-120)

Longitudinally Stiffened Unsymmetrical

Sections 10.49.3.1 Longitudinal stiffeners shall be required on unsymmetrical sections when the web thickness is less than that specified by Articles 10.48.5.1 or 10.49.2.

10.49.3.2 For girders with one longitudinal stiffener and transverse stiffeners, the provisions of Article 10.48.6 for symmetrical sections shall be applicable provided that: (a) When D exceeds D/2, the longitudinal stiffener is placed 2D, /5 from the inner surface or the leg of the compression flange element. (b) When D~ exceeds D/2, the web thickness. t~. shall meet the requirement:

D~ j~ is the product of area and yield point for web of steel section. (b) The depth of the stress block is computed from the compressive force in the slab. C-(AF

yc

0. 85fb

(10-125)

(c) When the compressive force in the slab is less than

the value given by Equation (10-123), the top portion of the steel section will be subjected to the compressive force on the next page:

DIVISION I—DESIGN

10.50.1.1.1

285

noncomposite or composite negative-moment pier see-

C’

=

(10-126)

2

(d) The location of the neutral axis within the steel section measured from the top of the steel section may

tions shall be taken as: forD,=D’ M. =M~

be determined as follows: for D’,= SD’

for

C’

t

(AF>, )mf for —

t1f +

1f

(10-127)

C’=(AFY)tf

C’ —(AF~ )mf D (AFy)w

M~

=

5M~ —0.85M>, 4

(10- 128)

10.50.1.1.2 Composite beams and girders in positive-moment regions shall qualify as compact when the web of the steel section satisfies the following requirement: 2D~~ < 19,230 (10-129) F~

where Do>, is the depth of the web in compression at the

plastic moment calculated in accordance with Article l0.S0.l.l.l, and t~ is the web thickness. Equation (10-129) is satisfied if the neutral axis at the plastic moment is located above the web; otherwise D~>, shall be computed as 5i from Equation (10-128) minus tim. Also, the distance

(10- 129a)

compute the transformed section properties.

In continuous spans with compact composite positivemoment sections, but with noncompact noncomposite or composite negative-moment pier sections, the maximum bending strength, M~, of the composite positive-moment sections shall be taken as either the moment capacity at first yield determined as specified in Article 10.50(0, or as: =

=

d

=

=

(MU

~

=

th

0.9 forE:, =36,000 psi; 0.7 for F:, = 50,000 psi;

depth of the steel beam or girder; thickness of the slab; thickness of the concrete haunch above the beam or girder top flange.

Equation (l0-129a) need not be checked for sections where the maximum flange stress does not exceed the specified minimum flange yield stress. The maximum bending strength, MU, of compact cornpt)site beams and girders in simple spans or in the positive-tnoment regions ot continuous spans with compact

M:, + A(MU —

(l0-129d)

where:

where:

=

0.85M>, Mp~B.~-’~ (l0-129c) 4yD’J

M~= plastic moment capacity of the composite positive moment section calculated in accordance with Article 10.50.1.1.1; = moment capacity at first yield of the composite positive moment section calculated as F:, times the section modulus with respect to the tension flange. The modular ratio, n, shall be used to

from the top of the slab to the neutral axis at the plastic moment, D>,, shall satisfy:

13

+

where:

(e) The maximum strength of the section in bending is the first moment of all forces about the neutral axis, taking all forces and moment arms as positive quantities.

(d + t~ + 7.5

(l0-129b)

A

= =

the moment capacity at first yield of the compact positive moment section calculated in accordance with Article 10.SO(f); Moment capacity of the noncompact section at the pier, MU, given by Article 10.48.2 or Article 10.48.4, minus the elastic moment at the pier, M~, for the loading producing maximum positive bending in the span. Use the smaller value of the difference for the two-pier sections for interior spans; I for interior spans; Distance from end support to the location of maximum positive moment divided by the span length for end spans.

M~ computed from Equation (l0-129d) shall not exceed the applicable value of MU computed from either Equation (l0-129b) or Equation (l0-129c). For continuous spans where the maximum bending strength of the positive-moment sections is determined

10.50. 1.1.2

HIGHWAY BRIDGES

286

from Equation (l0-129d), the maximum positive moment in the span shall not exceed M:,, for the loading which produces the maximum negative moment at the adjacent pier(s).

For composite sections in positive-moment regions not satisfying the requirements of Equation (10-129) or Equa-

tion (l0-129a), M~ shall be determined as specified in Article 10.50.1.2. 10.50.1.2

Noncompact Sections

10.50.1.2.1 When the steel section does not satisfy the compactness requirements of Article l0.50.l.l.2 the maximum bending strength, M5, of the section shall be

taken as the moment at first yield determined as specified in Article 10.50(f). 10.50.1.2.2 When the girders are not provided with temporary supports during the placing of dead loads, the sum of the stresses produced by I .30D, acting on the steel girder alone with l.30(D. + 5(L + 1)/3) acting on the composite girder shall not exceed yield stress at any point, where D~ and D~ are the moments caused by the dead load acting on the steel girder and composite girder, respectively.

SOW) meet these requirements. MU shall be computed as the resultant moment of the fully plastic stress distribution acting on the section including any composite rebars. If the distance from the neutral axis to the compression flange exceeds D/2, the compact section requirements given by Equations (10-93) and (10-94) must be modified by replacing D with the quantity ~ where D~1, is the depth of the web in compression at the plastic moment.

10.50.2.2

Noncompact Sections

When the steel section does not satisfy the compactness requirements of Article 10.50.2.1 but does satisfy the requirements of Article 10.48.2.1, the maximum strength, MU, of the section shall be taken as the moment at first yielding determined as specified in Article 10.50(f). If the requirements of Article 10.48.2.1(b) or Article 10.48.2.1(c) are not satisfied. M~ shall be calculated according to the provisions specified in Article 10.48.4.1. In this case, the web slenderness shall not exceed the requ irement given by Equation (10-103) or Equation (10108), as applicable, subject to the corresponding requirements of Article 10.49.2 or 10.49.3. 10.50.2.3

When the girders are provided with ef-

In the negative moment regions of continuous spans,

fective intermediate supports that are kept in place until the concrete has attained 75 percent of its required 28-day strength, stresses produced by the loading, I .30(D + 5(L ±1)/3), acting on the composite girder, shall not exceed yield stress at any point.

the minimum longitudinal reinforcement including the

10.50.1.2.3

longitudinal distribution reinforcement must equal or exceed 1 percent of the cross-sectional area of the concrete slab. Two-thirds of this required reinforcement is to be placed in the top layer of slab within the effective width. Placement of distribution steel as specified in Article

10.50.2

Negative Moment Sections of Composite Beams and Girders

3.24.10 is waived within the effective width. 10.50.2.4

The maximum bending strength, MU, of composite beams and girders in the negative moment regions shall be computed in accordance with Articles 10.48 and 10.49 as applicable. It shall be assumed that the concrete slab does not carry tensile stresses. In cases where the slab rein-

forcement is continuous over interior supports, the reinforcement may be considered to act compositely with the steel section. 10.50.2.1

Compact Sections

Composite beams and girders in negative bending qualify as compact when their steel section meets the re-

quirements of Article 10.48.1.1, and the stress-strain diagram of the steel exhibits a yield plateau followed by a strain hardening range. Steels such as AASHTO M 270 Grades 36. 50, and SOW (ASTM A 709, Grades 36, 50, and

When shear connectors are omitted from the negative

moment region, the longitudinal reinforcement shall be extended into the positive moment region beyond the an-

chorage connectors at least 40 times the reinforcement diameter. 10.51

COMPOSITE BOX GIRDERS*

This section pertains to the design of simple and continuous bridges of moderate length supported by two or more single-cell composite box girders. The distance cen5’For information regarding the design of long-span steel box girder bridges. Report No. FHWA-TS-80-205. ~Proposed Design Specifications for Steel Box Girder Bridges’ is available from the Federal Highway Administration.

DIVISION I—DESIGN

10.51

287

ter-to-center flanges of adjacent boxes shall be not greater

10.51.5

than 1.2 times and not less than 0.8 times the distance center-to-center of the flanges of each box. In addition to the above, when nonparallel girders are used the distance cen-

10.51.5.1 Unstiffened compression flanges designed for the yield stress, F:,, shall have a width-to-thickness ratio

ter-to-center of adjacent flanges at supports shall be not

equal to or less than the value obtained from the formula:

Compression Flanges

greater than 1 .35 times and not less than 0.65 times the distance

center-to-center of the flanges of each box. The

cantilever overhang of the deck slab, including curbs and parapet, shall be limited to 60 percent of the distance between the centers of adjacent top steel flanges of adjacent box girders, but in no case greater than 6 feet. 10.5 1.1

Maximum Strength

FcrS

=

6,140

b

F>,

t

13,300

(10-133)

F>,

the buckling stress of an unstiffened bottom flange is given by the formula: Fer =0.592F>,(l

0.687sin§fl

+

in which c shall be taken as,

b

13,300—--

Lateral Distribution

The live-load bending moment for each box girder shall be determined in accordance with Article 10.39.2. 10.51.3

(10-132)

where b = flange width between webs in inches, and t flange thickness in inches.

(10-130)

where F~, is the buckling stress of the bottom flange plate as given in Article 10.51.5. 10.5 1.2

6,140

10.51.5.2 For greater bit ratios,

The maximum strength of box girders shall be determined according to the applicable provisions of Articles 10.48, 10.49, and 10.50. In addition, the maximum strength of the negative moment sections shall be limited by: =

b

—

F>,

7,160 10.51.5.3

(10-134)

(10-135)

For values of, b

Web Plates

13,300

F>,

(10-136)

The design shear~ for a web shall be calculated using the buckling stress of the flange is given by the formula:

the following equation: =

V/cos 0

(10-13 1)

where V = one-half of the total vertical shear force on one box girder, and 0 = the angle of inclination of the web plate to the vertical. The inclination of the web plates to the vertical shall not exceed 1 to 4. 10.51.4

=

(10-137)

10.51.5.4 If longitudinal stiffeners are used, they shall be equally spaced across the flange width and shall be proportioned so that the moment of inertia of each stiffener about an axis parallel to the flange and at the base of the stiffener is at least equal to:

Tension Flanges

In the case of simply supported spans, the bottom flange shall be considered fully effective in resisting bending if its width does not exceed one-fifth the span length. If the flange plate width exceeds one-fifth of the span, only an amount equal to one-fifth of the span shall be considered effective. For continuous spans, the requirements above shall be applied to the distance between points of contraflexure.

2 X 106

105(tlb)

=

4 t3w

(10-138)

where:

4* 4* w

= = =

0.07k3n4 when n equals 2, 3, 4, or 5; 0.125k3 when n = I; width of flange between longitudinal stiffeners or distance from a web to the nearest longitudinal

n

=

stiffener; number of longitudinal stiffeners;

k

=

buckling coefficient which shall not exceed 4.

10.5 1.5.4.1

HIGHWAY BRIDGES

288 10.5 1.5.4.1

10.51.6

For a longitudinally stiffened flange designed for the yield stress F:,, the ratio w/t shall not exceed the value given by the formula:

w

3,070

(10- 139)

k

F>, 10.51.5.4.2

Diaphragms, cross-frames, or other means shall be

provided within the box girders at each support to resist transverse rotation, displacement, and distortion. Intermediate diaphragms or cross-frames are not required for box girder bridges designed in accordance with this specification. 10.52

For greater values of w/t,

10.52.1 3,070 k F>,

w

6,650 k

t

the buckling stress of the flange, including stiffeners, is given by Article 10.5 1.5.2 in which c shall be taken as:

w

F>,

(10- 141)

3,580 k 10.5 1.5.4.3

For values of,

w 6,650 k

SHEAR CONNECTORS General

(10- 140)

F>,

6,650 k—---

Diaphragms

(10-142)

The horizontal shear at the interface between the concrete slab and the steel girder shall be provided for by mechanical shear connectors throughout the simple spans and the positive moment regions of continuous spans. In the negative moment regions, shear connectors shall be provided when the reinforcing steel embedded in the concrete is considered a part of the composite section. In case the reinforcing steel embedded in the concrete is not considered in computing section properties of negative moment sections, shear connectors need not be provided in these portions of the span, but additional connectors shall be placed in the region of the points of dead load contraflexure as specified in Article 10.38.5.1.3.

F>, 10.52.2 Design of Connectors the buckling stress of the flange, including stiffeners, is The number of shear connectors shall be determined in

given by the formula: =

1 0.51.5.4.4

26.2k(tlw)2 X 10~

(10-143)

When longitudinal stiffeners are used, it

is preferable to have at least one transverse stiffener

placed near the point of dead load contraflexure. The stiffener should have a size equal to that of a longitudinal stiffener. 10.51.5.5 The width-to-thickness ratio of any outstanding element of the flange stiffeners shall not exceed the value determined by the formula:

accordance with Article 10.38.5.1.2 and checked for fatigue in accordance with Articles 10.38.5.1.1 and 10.3 8~5.I.3.

10.52.3

The maximum pitch shall not exceed 24 inches except over the interior supports of continuous beams where wider spacing may be used to avoid placing connectors at locations of high stresses in the tension flange. 10.53

h’

2,600

t’

F~.

(10-144)

where:

F:,

=

width of any outstanding stiffener element,

=

and; thickness of outstanding stiffener element; yield strength of outstanding stiffener ele-

=

ment.

Maximum Spacing

HYBRID GIRDERS

This section pertains to the design of girders that utilize a lower strength steel in the web than in one or both of the flanges. It applies to composite and noncomposite plate girders and to composite box girders. At any cross section where the bending stress in either flange caused by the maximum design load exceeds the minimum specified yield strength of the web steel, the compression-flange area shall not be less than the tension-flange area. The topflange area shall include the transformed area of any por-

)

tion of the slab or reinforcing steel that is considered to act compositely with the steel girder. The provisions of Articles 10.48 through 10.52, 10.57.1, and 10.57.2 shall apply to hybrid beams and girders except as modified below. In all equations of these articles, F:, shall be taken as the minimum specified yield strength of the steel of the element under consideration with the following exceptions: (1) In Articles 10.48.1.1(b), 10.48.2.1(b), 10.48.4.1, 10.48.5.1, 10.48.6.1, 10.49.2, 10.49.3.2(b), and 10.50(d) use the F:, of the compression flange. (2) In Articles 10.48.6.3(a) and 10.48.6.3(c) use the F:, of the adjacent flange. Articles 10.57.1 and 10.57.2 shall apply to the flanges, but not to the web of hybrid girders. The provision specified in Article 10.40.4 shall also apply. 10.53.1

289

DIVISION I—DESIGN

10.53

For unsymmetrical sections,

R

=

1— [f¾’(l —

10.53.1.3

The strength of unbraced noncompact hybrid sections shall be calculated in accordance with Article 10.48.4.1 with Equation (l0-103a) replaced by the expression: =

F:,5Z

(10-145)

where F:,f is the specified minimum yield strength of the flange, and Z is the plastic section modulus. In computing Z, the web thickness shall be multiplied by the ratio of the minimum specified yield strength of the web, F:,~, to the minimum specified yield strength of F:,f. Braced Noncompact Sections

The equation of Article 10.48.2 for the maximum strength of noncompact sections shall be replaced by the expression: =

MrRhR

(10- 148a)

and the yield moment calculated as: F>,~S R.

(10-148b)

where the appropriate R is determined from Article 10.53.1.2 above, and Rb is determined by Equation (10-

The equation of Article 10.48.1 for the maximum strength of compact sections shall be replaced by the expression:

10.53.1.2

PN’)] (10-148)

Unbraced Noncompact Sections

=

Compact Sections

=

+

where 4* is the distance from the outer fiber of the tension flange to the neutral axis divided by the depth of the steel section.

Noncomposite Hybrid Girders

10.53.1.1

—

(10-146)

F:,fSR

103b). 10.53.1.4 Transversely Stiffened Girders Equation (10-114) of Article 10.48.8.1 for the shear ca-

pacity of transversely stiffened girders shall be replaced by the expression: (10-149) The provisions of Article 10.48.8.2, and the equation for A in Article 10.48.5.3 are not applicable to hybrid girders. 10.53.2 Composite Hybrid Girders The maximum strength of the composite section shall be the moment at first yielding of the flanges times R (for

unsymmetrical sections) from Article 10.53.1.2, in which 4* is the distance from the outer fiber of the tension flange to the neutral axis of the transformed section divided by the depth of the steel section.

For symmetrical sections: 3

12+2L3 R= 12+13(3p—p

(10—147)

10.54 10.54.1

where:

COMPRESSION MEMBERS Axial Loading

10.54.1.1

Maximum Capacity

The maximum strength of concentrically loaded

13=

Aw/Am

columns shall be computed as:

290

HIGHWAY BRIDGES PU

(10-150)

0.85AYcr

=

10.54.2

10.54.1.1 Combined Axial Load and Bending

10.54.2.1 where A~ is the gross effective area of the column cross section and F~, is determined by one of the following two formulas:

F~= F>,[l — 4Th2E(r~J

for

F.r

KL r~

r

=

2it2E F>,

itE

(10-151)

Maximum Capacity

The combined maximum axial force P and the maximum bending moment M acting on a beam-column subjected to eccentric loading shall satisfy the following equations:

P ______

(10- 153)

0.85A

5F>,

for

r KL~

2E

2itF>,

(10- 154)

Fcr

=

=

effective length factor in the plane of buckling; L~= length of the member between points of support in inches; r = radius of gyration in the plane of buckling in inches; F:,= yield stress of the steel in pounds per square inch; F = 29,000,000 pounds per square inch; Fcr= buckling stress in pounds per square inch.

+

M

~e~J AF =1.0

M~

(10- 156)

where:

where: K

r

______ + MC =1.0 (10-155) 0.85AsFcr M~ l—-—---P

(10- 152)

buckling stress as determined by the equations of Article 10.54.1.1; maximum strength as determined by Articles 10.48.1, 10.48.2, or 10.48.4;

=

ilhe Euler Buckling stress in the plane of bending; (10-157)

C

=

10.54.1.2 Effective Length

M~ Z

The effective length factor K shall be determined as

KL~

follows:

EIE2

=

r

equivalent moment factor, as defined below;

=F:,Z, the full plastic moment of the section; = =

plastic section modulus; effective slenderness ratio in the plane of bending.

(a) For members having lateral support in both directions at its ends:

10.54.2.2

K

=

If the ends of the beam-column are restrained from

K

=

0.75 for riveted, bolted, or welded end connections; 0.875 for pinned ends.

(b) For members having ends not fully supported lat-

erally by diagonal bracing or an attachment to an adjacent structure, the effective length factor shall be determined by a rational procedure.*

‘B. G. Johnston. Guide to Stability Design Criteria for Metal Structures, John Wiley and Sons, Inc., New York, 1976.

Equivalent Moment Factor C

sidesway in the plane of bending by diagonal bracing or attachment to an adjacent laterally braced structure, then

the value of equivalent moment factor, C, may be computed by the formula: C

=

0.6 + 0.4a, but not less than 0.4 (10-158)

where a is the ratio of the numerically smaller to the larger end moment. The ratio a is positive when the two end moments act in an opposing sense (i.e., one acts clockwise and the other acts counterclockwise) and negative when they act in the same sense. In all cases, factor C may be taken conservatively as unity.

10.55 10.55

DIVISION I—DESIGN SOLID RIB ARCHES

SPLICES, CONNECTIONS, AND DETAILS

10.56

See Article 3.2 for load factors and combinations. Use

Service Load Design Method for factored loads and the formulas changed as follows:

291

10.56.1

Connectors

10.56.1.1

General

Connectors and connections shall be proportioned so

10.55.1

Moment Amplification and Allowable Stresses I 18T I—

(10-159)

that their design resistance, 4*R, (maximum strength multiplied by a resistance factor) as given in this Article, as applicable, shall be at least equal to the effects of service loads multiplied by their respective load factors as specifled in Article 3.22.

—‘______

AFe

10.56.1.2 ___

1.18

L

(KL)2F

4&E

—

1

The ultimate strength of the weld metal in groove and fillet welds shall be equal to or greater than that of the base

JandFb= F:, (10-160)

Web Plates

10.55.2

=

6,750

(10- 161)

cations with strengths less than the base metal when detailing fillet welds for quenched and tempered steels. However, the welding procedure and weld metal shall be selected to ensure sound welds. The effective weld area

10.56.L3

Bolts and Rivets

10.56.1.3.1 In proportioning fasteners, the cross sectional area based upon nominal diameter shall be used.

One longitudinal stiffener, D/t~

10,150

(10-162)

13,500

(10-163)

Two longitudinal stiffeners,

D/t~

metal, except that the designer may use electrode classifi-

shall be taken as defined in ANSI/AASHTO/AWS DI.5 Bridge Welding Code, Article 2.3.

No longitudinal stiffener, D/t~

Welds

10.56.1.3.2 The design force, 4*R, in kips, for AASHTO M 164 (ASTM A 325) and AASHTO M 253 (ASTM A 490) high-strength bolts subject to applied axial tension or shear is given by: =

~FA5

(l0-166a)

where:

The b’/t, ratio for the stiffeners shall be: b’

——

2,200

b’ maximum —=12

-~

=

(10-164)

a

5,700

—

f-t-f

tf

b’

—

for width between webs (10-165)

a b 2,200 f±f a h

for overhang widths, maximumb’/t~ =12

=

The design bearing force, 4*R, on the connected material in standard, oversized, short-slotted holes loaded in any direction, or long-slotted holes parallel to the applied bearing force shall be taken as:

1055.3 Flange Plates b’

Ab

design strength per bolt area as given in Table l0.56A for appropriate kind of load, ksi; area of bolt corresponding to nominal diameter, sq in.

(10-166)

=

O9LtF

<

l.8dtF~

(l0-166b)

The design bearing force, ~R, on the connected material in long-slotted holes perpendicular to the applied bearing force shall be taken as:

292

10.56.1.3.2

HIGHWAY BRIDGES =

0.75L~tF ~ I 5dtF

(l0-166c)

ternal load and tension resulting from prying action produced by deformation of the connected parts. The total

The design bearing force for the connection is equal to the sum of the design bearing forces for the individual bolts in the connection.

tension should not exceed the values given in Table I 0.56A. The tension due to prying actions shall be computed as:

In the foregoing:

4R

= =

=

d

= =

design bearing force, kips. specified minimum tensile strength of the connected material, ksi. clear distance between the holes or between the hole and the edge of the material in the direction of the applied bearing force, in. nominal diameter of bolt, in. thickness of connected material, in.

10.56.1.3.3 High-strength bolts preferably shall be used for fasteners subject to tension or combined shear

and tension. For combined tension and shear, bolts and rivets shall be proportioned so that the tensile stress does not exceed:

for

f/F

Fm’ f

for

5/F5



(10-167) 0.33

F~’= FJI(f/F)2

=

F,

=

where:

Q

=

T

=

a b

prying tension per bolt (taken as zero when negative); direct tension per bolt due to external load; distance from center of bolt to edge of plate; distance from center of bolt to toe of fillet of connected part;

= =

thickness of thinnest part connected in inches.

=

10.56.3

10.56.3.2 The beam web shall equal or exceed the thickness given by: computed rivet or bolt stress in shear, ksi; design shear strength of rivet or bolt from Table l0.56A or Table l0.57A, ksi; design tensile strength of rivet or bolt from Table reduced design tensile strength of rivet or bolt due to the applied shear stress, ksi.

10.56.1.4

Slip-Critical Joints

Slip-critical joints shall be designed to prevent slip at the overload in accordance with Article 10.57.3, but as a

minimum the bolts shall be capable of developing the minimum strength requirements in bearing of Articles 10.18 and 10.19.

Potential slip of joints should be investigated at intermediate load stages especially those joints located in composite regions. 10.56.2

Rigid Connections

10.56.3.1 All rigid frame connections, the rigidity of which is essential to the continuity assumed as the basis of design, shall be capable of resisting the moments, shears, and axial loads to which they are subjected by maximum loads.

t~F>,dbdj

Bolts Subjected to Prying Action by Connected Parts

Bolts required to support applied load by means of direct tension shall be proportioned for the sum of the cx-

(10- 169)

where:

10.56A, ksi; =

(10-168)

(l0-167a)

where:

=

Q~Z[2~L]T

dh

=

column moment;

=

beam depth;

=

column depth.

When the thickness of the connection web is less than that given by the above formula, the web shall be strengthened by diagonal stiffeners or by a reinforcing

plate in contact with the web over the connection area. At joints where the flanges of one member are rigidly framed into one flange of another member, the thickness of the web, t~, supporting the latter flange and the thickness of the latter flange, k~ shall be checked by the formulas below. Stiffeners are required on the web of the second member opposite the compression flange of the first member when:

Af tb+Sk

(10-170)

293

DIVISION I—DESIGN

10.56.3.2

TABLE 10.S6A

Design Strength of Connectors

‘l~’pe of Fastener

Strength (~F)

Groove Weld’ Fillet Weld”

1.00 F~ 0.45 F~

Low-Carbon Steel Bolts ASTM A 307 Tension Shear on Bolt with Threads in Shear Plane Power-Driven Rivets ASTM A 502 Shear—Grade 1 Shear—Grade 2 High-Strength Bolts

30 ksi 18 ksi

25 ksi 30 ksi

AASHTO M 164

(ASTM A 325) Applied Static Tensionc Shear on Bolt with Threads in Shear Plane~~d~~ AASHTO M 253 (ASTM A 490) Applied Static Tension Shear on Bolt with Threads in Shear Planed,e = =

68 ksi 35 ksi 85 ksi 43 ksi

yield point of connected material. minimum strength of the welding rod metal but not greater than the tensile strength of

the connected parts.

UThe tensile strength of M 164 (A 325) bolts decreases for diameters greater than 1 inch. The design values listed are for bolts up to 1-inch diameter. The design values shall be multiplied by 0.875 for diameters greater than 1 inch. dTabulated values shall be reduced by 20 percent in hearing-type connections whose length between extreme fasteners in each ofthe spliced parts measured parallet to the line of axial foree exceeds 50 inches. tf material thickness or joint details preclude threads in the shear plane, multiply values by 1.25.

and opposite the tension flange of the first member when t< 0.4 Af

(10-171)

where: k

A1

tions, and F:,f is the specified minimum yield stress of the flange. For such beams and girders designed for Group IA loading, the maximum flange stress caused by D + 2.2(L + I) shall not exceed 0.8RF>,C. In the case of moment redistribution under the provisions of Article 10.48.1.3 the above limitation shall apply to the modified moments but

not to the original moments.

=

thickness of web to be stiffened;

=

distance from outer face of flange to toe of web

10.57.2

= =

fillet of member to be stiffened; thickness of flange delivering concentrated force; thickness of flange of member to be stiffened;

=

area of flange delivering concentrated load.

0.95RF:,~ where R is the hybrid girder reduction factor specified in Article 10.53.1.2, equal to 1.0 for nonhybrid

10.57 10.57.1

OVERLOAD

Noncomposite Beams and Girders

For noncomposite beams and girders, the maximum flange stress caused by D + 5(L + I)/3 shall not exceed 0.8RF:,~ where R is the hybrid girder reduction factor specified in Article 10.53.1.2, equal to 1 .0 for nonhybrid see-

Composite Beams and Girders

For composite beams and girders, the maximum flange stress caused by D + 5(L ±I)/3 shall not exceed

sections, and F:,f is the specified minimum yield stress of the flange. For such beams and girders designed for Group lA loading, the maximum flange stress caused by D + 2.2(L ± I) shall not exceed 0.9SRF:,f. In computing dead load stresses the presence or absence of temporary supports during the construction shall be considered.

10.57.2

HIGHWAY BRIDGES

294 TABLE l0.57A

Design Slip Resistance for Slip-Critical Connections = 4*Tbp., ksi)

(Slip Resistance per Unit ofBolt Area, 4*F,

Hole ‘I~pe and Direction of Load Application Any Direction Oversize and Short Slot

Standard AASHTO AASHTO M164 M253 Contact Surface of Bolted Parts

(ASTM A 325)

Class A (Slip Coefficient 0.33) Clean mill scale and blastcleaned surfaces with Class A coatings” Claus B (Slip Coefficient 0.50) Blast-cleaned surfaces and blast-cleaned surfaces with Class B coatings” Class C (Slip Coefficient 0.33) Hot-dip galvanized surfaces roughened by wire brushing after galvanizing

Transverse

(ASTM A 490)

Parallel

Long Slots

Long Slots

AASHTO M164

AASHTO M253

AASHTO M164

AASHTO M253

AASHTO M164

AASHTO M253

(ASTM A 325)

(ASTM A 490)

(ASTM A 325)

(ASTM A 490)

(ASTM A 325)

(ASTM A 490)

21

26

18

22

15

18

13

16

32

40

27

34

22

28

19

24

21

26

18

22

15

18

13

16

The tensile strength of M 164 (A 325) bolts decreases for diameters greater than 1 inch. The design values listed are for bolts up to Iinch diameter. The design values shall be multiplied by 0.875 for diameters greater than 1 inch. “Coatings classified as Class A or Class B include those coatings which provide a mean slip coefficient not less than 0.33 or 0.50, respectively, as determined by Testing Method to Determine the Slip Coefficient for Coatings Used in Bolted Joints. See Article 10.32.3.2.3.

10.57.3 Slip-Critical Joints

4*

10.57.3.1 In addition to the requirements of 10.56.1.3.1 and 10.56.1.3.2 for fasteners, the force caused by D 5(L + I)/3, for H or HS truck load only, on a slipcritical joint shall not exceed the design slip force (4*R,) given by:

=

1.0 for standard holes; 0.85 for oversized and short slotted holes;

=

0.70 for long slotted holes loaded transversely;

=

0.60 for long slotted holes loaded longitudinally.

=

-~-

Class A, B, or C surface conditions of the bolted parts as defined in Table l0.57A shall be used in joints designated as slip-critical except as permitted in Article 10.57.3.2.

=

4*F,A:,NhN,

(10-172)

=

4*T:,p, design slip resistance per unit of bolt area given in Table l0.57A, ksi; area corresponding to the nominal body area of the bolt, sq in.; number of bolts in the joint;

=

number of slip planes;

=

specified tension in the bolt;

=

slip coefficient;

10.57.3.2 Subject to the approval of the Engineer. coatings providing a slip coefficient less than 0.33 may be used provided the mean slip coefficient is established by test in accordance with the requirements of Article 10.57.3.3, and the slip resistance per unit area established. The slip resistance per unit area shall be taken as equal to the slip resistance per unit area from Table l0.57A for Class A coatings as appropriate for the hole type and bolt type times the slip coefficient determined by test divided by 0.33.

0.33 for clean mill scale and Class A coatings 0.50 for blast-cleatied surfaces and Class B coatings; 0.33 for hot-dip galvanized and roughened surfaces;

nections specified to be slip critical, shall be qualified by test in accordance with “Test Method to Determine the Slip Coefficient for Coatings Used in Bolted Joints” as

where: =

A:, N:, N,

p

=

= =

=

10.57.3.3

Paint, used on the faying surfaces of con-

10.57.3.3

DIVISION I—DESIGN

adopted by the Research Council on Structural Connections. See Appendix A of Allowable Stress Design Specification for Structural Joints Using ASTM A 325 or A 490 Bolts, published by the Research Council on Structural Connections. 10.57.3.4

For combined shear and tension in slip

critical joints where applied forces reduce the total clamping force on the friction plane, the design slip force shall not exceed the value ~R~’ obtained from the following equation: =

4*R~(l

—

l.88f!FU)

(10-173)

295

range of stress for fatigue shall conform to Article 10.3, except that the limitation imposed by the basic criteria

given in Article 10.3.1 shall not apply. 10.58.2

Composite Construction

10.58.2.1

Slab Reinforcement

When composite action is provided in the negative moment region, the range of stress in slab reinforcement shall be limited to 20,000 psi. 10.58.2.2

Shear Connectors

The shear connectors shall be designed fbr fatigue in

where: =

computed tensile stress in the bolt due to ap-

plied loads including any stress due to prying

accordance with Article 10.38.5.1. 10.58.3

Hybrid Beams and Girders

action. ksi; =

=

=

=

design slip force specified in Equation (10-172), kips; 120 ksi for M 164 (A 325) bolts up to I-inch diameter; 105 ksi for M 164 (A 325) bolts over I-inch diameter; 150 ksi for M 253 (A 490) bolts.

Hybrid girders shall be designed for fatigue in accordance with Article 10.3. 10.59

DEFLECTION

The control of deflection of steel or of composite steel

and concrete structures shall conform to the provision of Article 10.6.

10.58

FATIGUE

10.58.1

General

10.60

The analysis of the probability of fatigue of steel mem-

bers or connections under service loads and the allowable

ORTHOTROPIC SUPERSTRUCTURES

A rational analysis based on the Strength Design Method, in accordance with the specifications, will be considered as compliance with the specitications.

Section 11 ALUMINUM DESIGN 11.1

GENERAL

11.4

STRUCTURAL SUPPORTS FOR HIGHWAY

SIGNS, LUMINAIRES, AND TRAFFIC The purpose of this section is to provide a location for indexing aluminum design, material fabrication, and con-

SIGNALS

struction specifications. 11.2

The AASHTO Standard Specifications frr Structural Supports for Highway Signs, Luminaires and Traffic Signals shall be used for the design and preparation of plans and specifications, fabrication, and erection of aluminum

BRIDGES

sign supports, luminaires, and traffic signals. Welding shall conform to Section 10 of the current AWS DI.2

The Specifications for Alumi,mum Structures, Fifth Edition, December 1986, published by the Aluminum Association, Inc., as it applies to “Bridge and Similar Type Structures,” are intended to serve as a standard or guide for the preparation of plans and specifications and as a reference for designers, fabricators, and erectors of aluminum bridge and railing structures and their aluminum structural components. Welding shall conform to Section

Structural Welding Code—Aluminum, and workmanship

requirements for Class I structures. Special consideration may be given to certain support structures, which may be designed and fabricated according to the provisions ofArticle 11.2, Bridges.

10 of the current AWS Dl .2 Structural Welding Code— Aluminum, and workmanship requirements for Class II

11.5

structures. 11.3

BRIDGE RAILING

The design of aluminum bridge railing shall be governed by Article 2.7; the fabrication and erection shall conform to Section 6 of the Specifications for Aluminum

SOIL-METAL PLATE INTERACTION

SYSTEMS

Structures, Fifth Edition, 1986; and the welding shall conform to Section 10 of the current AWS Dl.2 Structural Welding Code—A luminuni, and workmanship requirements for Class II Structures. The AASI-ITO Roadside Design Guide should be consulted for guidance on the

The design of aluminum soil-metal plate interaction systems shall be in accordance with Section 12. Fabrication and installation shall be in accordance with Section 23—Division II.

safety considerations in the design of bridge rail.

297

12

SOIL-CORRUGATED METAL STRUCTURE INTERACTION SYSTEMS 12.1

GENERAL

12.1.1

k Mdl

Scope

The specifications of this Section are intended for the structural design of corrugated metal structures. It must be recognized that a buried flexible structure is a composite

=

crown

=

haunch

P

=

P

=

r

=

Notations =

AL C C 2 Cd

D

=

required wall area (Article 12.2.1)

=

area of pipe wall (Article 12.3.1)

=

=

=

FF

= =

= =

H

= =

rh

=

R

= =

total axle load on single axle or tandem axles (Articles 12.8.4.3.2 and 12.8.4.4)

capacity

(Article

plastic

moment

capacity

(Article

design load (Article 12.1.4) proportion of total moment carried by the crown. Limits for P are given in Table 12.7.4D (Article 12.8.4.3.3) radius of gyration of corrugation (Articles 12.2.2 and 12.3.2) radius of crown (Table 12.8.2A) radius of haunch (Table 12.8.2A) rise of box culvert (Articles 12.7.2 and 12.8.4.4) haunch moment reduction factor (Article

number of axles coefficient (Article 12.8.4.3.2)

S

=

12.8.4.3.3) diameter of span (Articles 12.1.4. 12.2.2. 12.8.2, and 12.8.4.4)

number of wheels per axle coefficient (Article

s

=

pipe diameteror span (Articles 12.2.4. 12.3.2. and

SF

=

12.3.4) safety factor (Article 12.2.3)

SS

=

required seam strength (Articles 12.2.3 and

12.8.4.3.2) = dead load adjustment coefficient 12.8.4.3.2) — live load adjustment coefficient 12.8.4.3.2) = straight leg of haunch (Article 12.8.2) =

moment

12.8.4.3.3)

Only Article 12.7 is applicable to structural plate box culverts.

A A

plastic

12.8.4.3.3) M~h

structure made up of the metal ring and the soil envelope, and that both materials play a vital part in the structural design of flexible metal structures.

12.1.2

= soil stiffness factor (Articles 12.2.2 and 12.3.2) = dead load factored moment (Article 12.8.4.3.3) = live load factored moment (Article 12.8.4.3.3)

(Article (Article

12.3.3) T Tm

modulus of elasticity of metal (Articles 12.2.2 and

=

=

12.3.2) modulus of elasticity of pipe material (Articles 12.2.4 and 12.3.4) flexibility factor (Articles 12.2.4 and 12.3.4)

=

V

= =

-y

allowable stress—specified minimum yield point divided by safety factor (Article 12.2.1) critical buckling stress (Articles 12.2.2 and 12.3.2)

=

=

specified minimum tensile strength (Articles 12.2.2 and 12.3.2) specified minimum yield point (Article 12.3. 1)

12.L3

height of cover above crown (Article 12.8.4.4) moment of inertia, per unit length, of cross section

thrust (Article 12.1.4) thrust, load factor (Articles 12.3.1 and 12.3.3) thrust, service load (Articles 12.2.1 and 12.2.3) length of stiffening rib on leg (Article 12.8.2) reaction acting in leg direction (Article 12.8.4.4) haunch radius included angle (Table 12.8. 2M unit weight of backfill (Articles 12.8.4.3,2 and 12.8.4.4) capacity modification factor (Articles 12.3.1 and 12.3.3)

Loads

Design load. P, shall be the pressure acting on the strtmc-

ture. For earth pressures, see Article 3.20. For live load, see Articles 3.4 to 3.7. 3.11, 3.12, and 6.4. except that the

of the pipe wall (Articles 12.2.4 and 12.3.4)

299

HIGHWAY BRIDGES

300

words “When the depth of fill is 2 feet or more” in Article 6.4.1 need not be considered. For loading combinations, see Article 3.22. 12.1.4

12.1.4.1 The thrust in the wall shall be checked by three criteria. Each considers the mutual function of the metal wall and the soil envelope surrounding it. The critena are: (a) Wall area; (b) Buckling stress;

(c) Seam strength (structures with longitudinal seams).

S —

2

12.1.6.2

T

= =

design load, in pounds per square foot;

diameteror span, in feet; thrust, in pounds per foot.

12.1.43 Handling and installation strength shall be sufficient to withstand impact forces when shipping and placing the pipe. 12.1.5

Materials

The materials shall conform to the AASHTO specifications referenced herein. 12.1.6

Soil Design

12.1.6.1

Pipe Arch Design

(12-I)

where: =

(1) Trench installations—2-feet minimum each side of culvert. This recommended limit should be modified as necessary to account for variables such as poor insitu soils. (2) Embankment installations—one diameter or span each side of culvert. (3) The minimum upper limit of the soil envelope is I foot above the culvert.

The thrust in the wall is: T=Px

P S

(3) The density of the embankment material above the pipe must be determined. See Article 6.2. (b) Dimensions of soil envelope. The general recommended criteria for lateral limits of the culvert soil envelope are as follows:

Design

12.1.4.2

12.1.3

Soil Parameters

The performance of a flexible culvert is dependent on soil structure interaction and soil stiffness. The following must be considered: (a) Soils: (I) The type and anticipated behavior of the foundation soil must be considered; i.e., stability for bedding and settlement under load. (2) The type, compacted density, and strength properties of the soil envelope immediately adjacent to the pipe must be established. Good side fill is obtamed from a granular material with little or no plas-

ticity and free of organic material, i.e., AASHT() classitication groups A-I, A-2. and A-3, compacted to a minimum 90 percent of standard density based on AASHTO Specifications T 99 (ASTM D 698).

The design of the corner backfill shall account for corner pressure which shall be considered to be approximately equal to thrust divided by the radius of the pipe arch corner. The soil envelope around the corners of pipe arches shall be capable of supporting this pressure. 12.1.6.3

Arch Design

12.1.6.3.1 Special design considerations may be applicable; a buried flexible structure may raise two important considerations. The first is that it is undesirable to make the metal arch relatively unyielding or fixed compared with the adjacent sidefill. The use of massive footings or piles to prevent any settlement of the arch is generally not recommended. Where poor materials are encountered, consideration should be given to removing some or all of this poor material and replacing it with acceptable material.

The footing should be designed to provide uniform longitudinal settlement, of acceptable magnitude from a functional aspect. Providing for the arch to settle will protect it from possible drag down forces caused by the consolidation of the adjacent sidefill. The second consideration is bearing pressure of soils under footings. Recognition must be given to the effect of depth of the base of footing and the direction of the footing reaction from the arch. Footing reactions for the metal arch are considered to act tangential to the metal plate at its point of connection

to the footing. The valtme of the reaction is the thrust in the metal arch plate at the footing. 12.1.6.3.2 Invert slabs and other appropriate incasures shall be provided to anticipate scour.

12.1.7

DIVISION I—DESIGN

12.1.7

12.2.2

Abrasive or Corrosive Conditions

Extra metal thickness, or coatings, may be required for to corrosion and abrasion. For highly abrasive conditions, a special design may be required. resistance

301

Buckling

Corrugations with the required wall area, A, shall be checked for possible buckling. If the allowable buckling stress, f0/SF, is 1e.s than f., the required area must be recalculated using fjSF in lieu of f,. Formulae for buckling

12.1.8

are:

Minimum Spacing

When multiple lines of pipes or pipe arches greater than 48 inches in diameter or span are used, they shall be spaced so that the sides of the pipe shall be no closer than one-half diameter or 3 feet, whichever is less, to permit

IfS

rj24E~

then ~cr=~u

r

lfS( 1172 configurations. (2) For installations 12.5.2.2:

0.383

0.524 0.373 6.080 0.883 0.355 9.260 Note: Effective section properties at full yield stress.

0.135

Section

for ¼X ¼X 772 configurations. 33 for ¼X I X 1172 configurations.

1033

FE = Note: I is the applicable moment of inertia value from Section 12.5.4.2.

I x 11½Configuration

X

3/4

I

A, (sq inift)

r (in.)

Ixl03 (in’/in.)

0.3t2 0.427

0.3% 0.391

4.080 5.450

0.697 1.009

0.380 0.369

8.390 11.480

Note: Effective section properties at full yield stress.

12.5.3.3 Minimum Cover 12.5.5 The minimum cover for design loads shall be measured from the top of rigid pavement or the bottom of flexible pavement such that:

(a) For steel conduits the minimum cover shall be span!4, but not less than 12 inches; (b) For aluminum conduits with spans of 48 inches or less, the minimum cover shall be span/2, but not less than 12 inches. For aluminum conduits with spans greater than 48 inches, the minimum cover shall be spanl2.75, but not less than 24 inches.

Chemical and Mechanical Requirements

12.5.5.1 Steel Spiral Rib Pipe and Pipe-Arch Requirements—AASHTO M 218 Mechanical Properties for Design Minimum Tensile Strength (psi)

Minimum (psi)

Modulus of Elasticity (psi)

45,000

33,000

29 x 106

12.5.5.2

For construction requirements, see Article 23.10— Division II.

Yield

Point

Aluminum Spiral Rib Pipe and Pipe-Arch Requirements—AASHTO M 197 Mechanical Properties for Design

Tensile Strength

Minimum Yield Point

Modulus of Elasticity

(psi)

(psi)

(psi

31,000

24,000

10 x l0~

Minimum

12.6

12.6 12.6.1

307

DIVISION I—DESIGN

STRUCTURAL PLATE PIPE STRUCTURES

12.6.2

Seam Strength Minimum Longitudinal Seam Strengths

General

12.6.1.1

Structural plate pipe, pipe-arches, and

arches shall be bolted with annular corrugations only. The specifications are: Aluminum AASHTO M 219

12.6.1.2

Steel AASHTOM 167

Service Load Design—safety factor, SF

Thickness (in.) 0.109 0.138 0.168 0.188 0.218 0.249 0.280

Seam strength = 3.0 Wall area = 2.0 Buckling = 2.0

12.6.1.3

Load Factor Design—Capacity Modification Factor, 4)

4) 12.6.1.4

=

Thickness (in.)

0.67

Flexibility Factor

(a) For steel conduits, FF should generally not exceed the following values: 6 in. 6 in.

X

6 in.

X

X

2 in. corrugation FF 2 in. corrugation FF arch) 2 in. corrugation FF

X

10-2 (pipe-

=

3.0

X

l0~ (arch)

(b) For aluminum conduits, FF should generally not exceed the following values: 9 in. 9 in. 9 in. 12.6.1.5

X 272

in. corrugation FF

X 272

in. corrugation FF arch) in. corrugation FF

>K

272

=

2.5 X 10~ (pipe) 3.6 X 102 (pipe-

=

7.2

=

X 102

3/4 3/4 3/4 3/4 3/4 3/4 3/4

43.0 62.0 81.0 93.0 112.0 132.0 144.0

180

194

9” x 2 ½” Aluminum Structural Plate Pipe Steel Bolts Aluminum Bolts 5½Bolts 5½Bolts Bolt Size Per ft Per ft (in.) (kips/ft) (kips/ft) 3/4 3/4 3/4 3/4 3/4 3/4 3/4

28.0 41.0 54.1 63.7 73.4 83.2 93.1

26.4 34.8 44.4 52.8 52.8 52.8 52.8

(pipe)

2.0 3.0

X 102

=

=

0.100 0.125 0.150 0.175 0.200 0.225 0.250

6” x 2” Steel Structural Plate Pipe Bolt Size 4 Bolts/ft 6 Bolts/ft 8 Bolts/ft (in.) (kips/ft) (kips/ft) (kips/ft)

(arch)

Minimum Cover

The minimum cover for design loads shall be SpanI8 but not less than 12 inches. (The minimum cover shall be measured from the top of a rigid pavement or the bottom of a flexible pavement.) For construction requirements, see Article 23.10—Division II.

12.6.3

Section Properties

12.6.3.1

Steel Conduits

Thickness (in.)

A~ (sq in./ft)

0.109 0.138 0.168 0.188 0.218 0.249 0.280

1.556 2.003 2.449 2.739 3.199 3.650 4.119

12.6.3.2

6” x 2” Corrugations r I x 4/in.) l0-~ (in.) (in. 0.682 0.684 0.686 0.688 0.690 0.692 0.695

60.411 78.175 96.163 108.000 126.922 146.172 165.836

Aluminum Conduits

Thickness (in.)

A~ (sq inift)

0.100 0.125 0.150 0.175 0.200 0.225 0.250

1.404 1 750 2 100 2449 2.799 3.149 3.501

9” x 2½”Corrugations r I x I0~ (in.) (in.4/in.) 0.8438 0 8444 0.8449 08454 08460 0.8468 0.8473

83.065 103.991 124.883 145.895 166.959 188.179 209.434

308

12.6.4

HIGHWAY BRIDGES

12.6.4

Chemical and Mechanical Properties

12.6.4.1

Aluminum Structural Plate Pipe, PipeArch, and Arch Material Requirements—AASHTO M 219, Alloy

12.7.2

Design

12.7.2.1

5052

Mechanical Properties for Design

Thickness

Minimum Tensile Strength

Minimum Yield Point

Mod. of Elast.

(in.)

(psi)

(psi)

(psi)

0. 100 to 0.175 0.176to0.250

35,000 34,000

24,000 24,000

10 X 106 lOx 106

12.6.4.2

construction and installation shall conform to Section 26—Division II.

Steel Structural Plate Pipe, Pipe-Arch, and Arch Material Requirements— AASHTO M 167

Mechanical Properties for Design Minimum Tensile

Minimum

Strength

Point (psi)

(psi) 45,000

Yield

33,000

Mod. of Elast.

(psi)

General

Long-span structures shall be designed in accordance with Articles 12.1 and 12.6, and 12.2 or 12.3 except that the requirements for buckling and flexibility factor shall not apply. The span in the formulae for thrust shall be re-

placed by twice the top arc radius. Long-span structures shall include acceptable special features. Minimum requirements are detailed in Table 12.7.IA.

TABLE 12.7.IA Minimum Requirements for Long-Span Structures with Acceptable Special Features I. TOP ARC MINIMUM THICKNESS

IS 6” x 2” Corrugated SteelPlates

15-17

Top Radius (ft) 17-20 20-23

23-25

0.lO9in. 0.138in. 0.168in. 0.218in. 0.249in.

29 x 106 II. MINIMUM COVER IN FEET

12.6.5

The design of structural plate arches should be based

on ratios of a rise to span of 0.3 minimum. 12.7

LONG-SPAN STRUCTURAL PLATE STRUCTURES

12.7.1

TOP RADIUS (Fl’)

Structural Plate Arches

General

Long-span structural plate structures are short-span bridges defined as follows. 12.7.1.1 Structural plate structures (pipe, pipe-arch, and arch) that exceed the maximum sizes imposed by Article 12.6. 12.7.1.2

Special shapes of any size that involve a rel-

atively large radius of curvature in crown or side plates. Vertical ellipses, horizontal ellipses, underpasses, low profile arches, high profile arches, and inverted pear shapes are the terms describing these special shapes. 12.71.3 Wall strength and chemical and mechanical properties shall be in accordance with Article 12.6. The

Steel 4 Thickness in inches

15

15-17

17-20

.109

2.5

.138

2.5 2.5

3.0 3.0

3.0

2.5 2.0 2.0 2.0

3.0

3.0

2.5

2.5 2.5 2.5

.168 .188 .218 .249 .280

2.0 2.0

20-23

23-25

3.0 3.0 3.0

4.0 4.0

Ill. GEOMETRIC LIMITS A. B. C. D.

MaximumPlate Radius—25 Ft. Maximum Central Angle of Top Arc 80” Minimum Ratio, Top Arc Radius to Side Arc Radius = 2 Maximum Ratio, Top Arc Radius to Side Arc Radius = 5* *Note: Sharp radii generate high soil bearing pressures. Avoid high ratios when significant heights of fill are involved.

IV. SPECIAL DESIGNS Structures not deseribed herein shall be regarded as special designs. “When reinforcing ribs are used the moment of inermia of the composite section shall be equal to or greater than the moment of inertia ofthe minimum plate thickness shown.

12.7.22

309

DIVISION I—DESIGN

12.7.2.2

Acceptable Special Features

(a) Continuous longitudinal structural stiffeners connected to the corrugated plates at each side of the top

(b) Uniform sand or gravel. (c) Approved stabilized soil shall be used only under direct supervision of a competent, experienced soils Engineer. Plastic soils shall not be used.

arc. Stiffeners may be metal or reinforced concrete either singly or in combination. (b) Reinforcing ribs formed from structural shapes curved to conform to the curvature of the plates, fastened to the structure as required to ensure integral action with the corrugated plates, and spaced at such intervals as necessary to increase the moment of inertia

of the section to that required by the design. 12.7.2.3 Design for Deflection Soil design and placement requirements for long-span

structures limit deflection satisfactorily. However, construction procedures must be such that severe deformations do not occur during construction. 12.7.2.4 Soil Design 12.7.2.4.1

12.7.2.4.2 The structure backfill material shall conform to one of the following soil classifications from AASHTO Specification M 145, Table 2: for height of fill less than 12 feet, A-I , A-3, A-2-4, and A-2-5; for height of fill of 12 feet and more, A-I, A-3. Structure backfill shall be placed and compacted to not less than 90-percent den-

sity per AASHTO T 180. 12.7.2.4.3

The extent of the select structural backfill

about the barrel is dependent on the quality of the adjacent embankment. For ordinary installations, with good quality, well-compacted embankment or in situ soil adjacent to the structure backfill, a width of structural backfill 6 feet beyond the structure is sufficient. The structure back-

fill shall also extend to an elevation 2 to 4 feet over the structure.

Granular type soils shall be used as struc-

ture backfill (the envelope next to the metal structure). The order of preference of acceptable structure backfill materials is as follows:

12.7.2.4.4 It shall not be necessary to excavate native soil at the sides if the quality of the native soil is as good

(a) Well-graded sand and gravel; sharp, rough, or an-

top shall also be select and shall be carefully and densely

gular if possible.

compacted.

as the proposed compacted side fill except to create the minimum width that can be compacted. The soil over the

310 12.7.3

HIGHWAY BRIDGES

12.7.3

Structural Plate Shapes

cii ROUND

VERTICAL

PIPE ARCH

ELLiPSE

ARcH

UNOERPASS

LOW

HORIZONTAL ELLIPSE

PROFILE ARCH

HIGH

INVERrEO

PROFILE ARCH

PEAR

FIGURE 12.7.lA. Standard Terminology of Structural Plate Shapes Including Long-Span Structures 12.7.4

End Treatment

When headwalls are not used, special attention may be necessary at the ends of the structure. Severe bevels and skews are not recommended. For hydraulic structures, additional reinforcement of the end is recommended to secure the metal edges at inlet and outlet against hydraulic forces. Reinforced concrete or structural steel collars, tension tiebacks or anchors in soil, partial headwalls and cut-off walls below invert eleva-

tion are some of the methods which can be used. Square ends may have side plates beveled up to a maximum 2:1 slope. Skew ends up to 150 with no bevel are permissible, but when this is done on spans over 20 feet the cut

edge must be reinforced with a reinforced concrete or structural steel collar. When full headwalls are used and they are skewed, the offset portion of the tnetal structure shall be supported by the headwall. A special headwall shall be designed for skews exceeding 150. The maximum skew shall be limited to 350

12.7.5

Multiple Structures

Care must be exercised on the design of multiple, closely spaced structures to control unbalanced loading.

Fills should be kept level over the series of structures when possible. Significant roadway grades across a series of structures require checking of the stability of the flexible structures under the resultant unbalanced loading. 12.8

12.8.1

STRUCTURAL PLATE BOX CULVERTS

General

Structural plate box culverts (hereafter “box culverts”) are composite reinforcing rib-plate structures of approximate rectangular shape. Box culverts are intended for shallow covers and low wide waterway openings. The shallow covers and extreme shapes of box culverts require special design procedures. Requirements of Articles 12.1

through 12.7 are not applicable to box culvert designs urmless included in Article 12.8 by specific reference.

12.8.1.1

DIVISION I—DESIGN

TABLE 12.8.2A Geometric Requirements for Box Culverts I. II. Ill. IV. V. VI. VII.

firmed by representative flexural test data. (Reference Artide 10.48.1).

Span, (5), may vary from 8 ft-9 in. to 25 ft-5 in. Rise, (R), may vary from 2 ft-6 in. to 10 ft -6 in. Radius of crown, (r 0) = 24 ft-9½ in. maximum Radius of haunch, (r,.J = 2 ft -6 in. minimum ~ may vary from 50” to 70” Length of leg, (D), may vary from 0.5 ft to 5.2 ft.

1%8.3 Structure Backfill 12.8.3.1

imum 95 percent of standard density based on AASHTO Specifications T-99 or 90 percent of standard density based on AASHTO Specifications T-180.

Scope

Article 12.8 presents structural capacity requirements for box culverts based on the load factor method. Standard shapes, soil requirements, and permissible product details for box culverts in compliance with this specification are defined. 12.8.2

Structure backfill material shall conform to

the requirements of Article 12.7.2.4, compacted to a min-

Minimum length of rib on leg, (in), is either 19 in. or the length of leg, (D), minus 3 in., whichever is less.

12.8.1.1

311

12.8.3.2 Specified structure backfill material shall be 3 feet wide, minimum, at the footing and shall extend upward to the road base elevation. 12.8.4

Design

12.8.4.1

Analytical Basis for Design

Structural requirements for box culverts have been developed from finite element analyses covering the range of structures allowed by Article 12.8.2.

Structural Standards

The design criteria presented in subsequent articles are

applicable only to structures in compliance with the standards described in Article 12.8.

12.8.4.1.1 Structural requirements are based on analyses using two dimensional live loads equivalent to

HS-20, 4-wheel, single-axle vehicles. Dead load of soil 12.8.2.1 Structural plate box culverts shall be bolted. The box culvert materials specitications are:

Alum i numn AASHTO M 219 12.8.2.2

Steel AASHTOM 167

Reinforcing ribs shall be an aluminum or

steel structural section curved to fit the structural plates. Ribs shall be bolted to the plates so as to develop the plastic moment capacity required. Spacing between ribs shall not exceed 2 feet on the crown and 4.5 feet on the haunch. Rib splices shall develop the plastic moment capacity required at the location of the splice. 12.8.2.3 Plastic moment capacities of ribbed sections may be computed using minimum yield strength values for both rib and corrugated shell. Such computed values may be used for design only after they have been con-

equals 120 pounds per cubic foot. Coefficients to adjust for other load conditions are contained in Article 12.8.4.3.2. 12.8.4.1.2 Backfill required in Article 12.8.3 is dense granular material. The analyses that provide the basis for this specification were based on conservative soil properties of low plasticity clay (CL) compacted to 90 percent of standard AASHTO Specifications T-99.

12.8.4.2

Actual moments from the analyses have been load factored to obtain the total plastic moment capacities required for box culverts. Load factors applied and included in Tables 12.8.4A and 12.8.4B are: Dead load, load factor = 1 .5 Live load, load factor = 2.0

Cro,.,~

12.8.4.3

•aunch

Load Factor Method

Plastic Moment Requirements

R t

Eod

of

Analyses covering the range of box culvert shapes described in Article 12.8.2 have shown moment requirements govern the design in all cases. Effects of thrust were

Rib

S

Standard Terminology of Structural Plate Box Culvert Shapes

FIGURE 12.8.2A

found to be negligible when combined with moment.

Metal box culverts act similar to rigid frames, distributing moment between the crown and haunch on the basis

HIGHWAY BRIDGES

312

of their relative stiffness. Within limits, increasing the stiffness of one component of the box (either crown or haunch) reduces the portion of the total moment carried

by the other. Article 12.8 provides for this moment distribution within the allowable limits of the moment proportioning factor (P). P represents the proportion of the total moment

C1

=

C1 C1 S C2

= =

12.8.4.3.1 The sum of the factored crown and haunch dead and live load moments are given in Tables 12.8.4A and 12.8.4B for standard dead and live load conditions.

Box culvert span in feet;

=

Adjustment coefficient for number of wheels

per axle. (Values for C2 are given in Table 12. 8.4C.)

TABLE 12.8.4B C~ M,.1 , Load Factored Live Load Moment for HS-20, 4-Wheel Single Axle, (C0 = 1.0), kip-ftlft Cover Depth, ft Span ft

1.40~

2.00

3.00

4.00

5.00

8 10

10.44 13.64

8.44 11.04

5.73 7.49

4.44 5.80

3.60 4.71

12

16.98

13.74

9.32

7.22

5.86

14 16 18

20.43 23.98 27.62

16.53 19.40 22.35

11.21 13.16 15.16

8.69 10.20 11.75

7.05 8.27 9.53

20

31.35

25.36

17.20

13.33

10.81

22

33.39

27.01

18.32

14.20

11.51

24 26

35.11 36.51

28.40 29.53

19.27 20.03

14.93 15.52

12.11 12.59

Moments for intermediate spans and covers may be linearly interpolated.

TABLE 12.8.4A Cd, Mdl, Load Factored Dead Load Moment for Soil Density of 120 lbfft3, (Cdl LO), kip-ftlft Cover Depth, ft

Span ft

1.40*

2.00

3.00

4.00

5.00

8 10

0.58

0.94 1.61

1.55

2.16

2.77

3.52

4.47

12 14

1.65 2.38 3.20

5.22 7.24

6.59 9.11

8.33

7.11 9.00 10.97 12.95

9.55 12.09 14.79 17.56

11.99 15.18 t8.60 22.18

9.32 10.01

14.81 16.46

20.31 22.91

25.80 29.35

*

1.04

16 18

7.16

5.56 6.02 6.14

22

24 26 *

4.67 5.91

4.05 4.87

20

2.57 3.85 5.37

2.47 3.50

Minimum cover depth from box culvert rise to top of pavement.

12.8.4.3.2 Dead and live load crown and haunch moments are adjusted for other loading conditions using the following adjustment coefficients: Cdl

=

y/120

(12-12)

C 0

=

CC.,(AL132)

Adjustment coefficient for number of axles; 1.0, forsingle axle; (0.5 + S/SO), for tandem axles, (C1 ~ 1.0);

=

that can be carried by the crown of the box culvert and varies with the relative moment capacities of the crown and haunch components. Limits for P are given in Table I 2.8.4D.

12.8.4.3

Minimum cover depth from box culvert rise to top of pavement.

C2, Adjustment coefficient Values for Number of Wheels per Axle

TABLE 12.8.4C Wheels per

Cover Depth, ft

Axle

1.4

2.0

3.0

2 4

1.18 1.00

1.21

1.24

1.00

1.00

8

0.63

0.70

0.82

5.0 1.02

1.00 0.93

12.8.4.3.3 Crown plastic moment capacity (Mpc), and haunch plastic moment capacity (Mph), must be equal to or greater than the proportioned sum of load adjusted dead and live load moments.

(12-13)

= P[(CdM~) + (C11M11)]

(12-14)

where: M~h = (1.0

Cd

y

=

Dead load adjustment coefficient; Backfill unit weight in pounds per cubic foot:

C,1

=

Live load adjustment coefficient for axle loads

where:

other than 32 kips, loads on tandem axles, and axles with other than 4 wheels; Total axle load on single axle or tandem axles in kips;

P

AL

=

=

=

—

P)[(CdiMd,)

+

(R5CIMJI)]

(12-15)

Proportion of total moment carried by the crown.

Limits for P are given in Table 12.8.4D; Rh

=

Haunch moment reduction factor from Table I 2.8.4E.

12.8.4.3.3

TABLE 12.8.4D

P, Crown Moment Proportioning Values Allowable Range of P

Span ft

Less Than 10 15—20 20—26

TABLE 12.8.4E

V

0.45 to 0.60

=

2/40,000)

y(HS/2,000 ± S + ALI[8 + 2(H + R)]

(12-16)

where:

Ri,, Haunch Moment Reduction Values

2

3

4to5

0.74

0.87

1.00

12.8.4.3.4 Article 12.8 can be used to check the adequacy of manufactured products for compliance with the requirements of this specification. Using the actual crown moment capacity (Mpc) provided by the box culvert under consideration and the loading requirements

of the application, Equation 12-14 is solved for the factor P. This factor should fall within the allowable range of Table 12.8.4D. Knowing the factor P, equation 12-15 is then solved for Mph, which should be less than or equal to the actual haunch moment capacity provided. If Equation 12-14 indicates a higher P factor than permitted by the ranges of Table 12.8.4D, the actual crown is over designed, which is acceptable. However, in this case only the maximum value of P allowed by the table

shall be used to calculate the required Mph from Equation 12-15.

Footing Reactions

The reaction at the box culvert footing may be computed using the following equation:

Cover Depth, ft

0.66

12.8.4.4

0.55 to 0.70 0.50 to 0.70 0.45 to 0.70

10—IS

1.4

313

DIVISION I—DESIGN

V

=

-y

=

H

=

S AL R

12.8.5

Reaction in kips per foot acting in the direction of the box culvert straight side; Backfill unit weight in pounds per cubic foot; Height of cover over the crown in feet;

=

Span of box culvert in feet; Axle load in kips;

=

Rise of box culvert in feet.

=

Manufacturing and Installation

12.8.5.1 Manufacture and assembly of structural plates shall be in accordance with Articles 23.2.1, and 23.3.1.4. Reinforcing ribs shall be attached as shown by the manufacturer. Bolts connecting plates, plates to ribs and rib splices shall be torqued to 150-foot pounds. 12.8.5.2

Sidefill and overfill per Article 12.8.3 shall

be placed in uniform layers not exceeding 8 inches in compacted thickness at near optimum moisture with equipment and methods which do not damage or distort the box culvert.

12.85.3 Following completion of roadway paving, crown deflection due to live load may be checked. After a minimum of 10 loading cycles with the design live load, the change in rise loaded with the design live load relative to the rise unloaded, should not exceed 72~ of the box

culvert span.

Section 13 WOOD STRUCTURES 13.1

GENERAL AND NOTATIONS =

13.1.1

Cb

=

Cf

=

loads applied perpendicular to the wide face of the laminations (Article 13.6.4.3) bearing area factor (Article 13.6.6.3) form factor (Article 13.6.4.5)

Cf~

=

fiat use factor for sawn lumber (footnotes to

Cr

=

General

The following information on wood design is generally based on the National Design Specification for Wood Construction (NDS®), 1991 Edition. See the 1991 Edition

Table 13.5.IA)

of the NDS® for additional information. 13.1.2

Net Section

d dmax

In determining the capacity of wood members, the net section of the member shall be used. Unless otherwise noted, the net section shall be determined by deducting from the gross section, the projected area of all material

=

repetitive member factor for sawn lumber (footnotes to Table 13.5.IA) depth of member (Article 13.6.4.2.2) maximum column face dimension (Article

=

minimum column face dimension (Article

=

representative dimension for a tapered column

=

13.7.3.4.2) 13.7.3.4.2)

removed by boring, grooving, dapping, notching or other means.

13.1.3

face (Article 13.7.3.4.2) E

=

Impact =

a

=

CF

CF CF

= = =

=

=

1

Cmi C,.

= = =

of

elasticity

(Article

allowable

modulus

of

elasticity

(Article

=

coefficient based on support conditions for ta-

=

adjusted tabulated bending stress for beam sta-

=

13.6.4.1) bility (Article 13.6.4.4.5) =

width of bending member (Article 13.6.4.3) load duration factor (Article 13.5.5.2) bending size factor for sawn lumber, structural composite lumber, and for glued laminated timber with loads applied parallel to the wide face of the laminations (Article 13.6.4.2) compression size factor for sawn lumber (footnotes to Table 13.5.IA) tension size factor for sawn lumber (footnotes to Table 13.5.IA) and structural composite lumber (footnotes to Tables 13.5.4A and

=

tabulated unit stress in compression parallel to grain (Article 13.7.3.2) allowable unit stress in compression parallel to

grain (Article 13.7.3.2) F~*

=adjusted tabulated stress in compression parallel to grain for column stability (Article 13 9) = actual unit stress in compression parallel to grain =

13.5.4B) C

modulus

Notations

Fb

pered columns (Article 13.7.3.4.2)

b C[)

tabulated 13.6.3)

13.6.3) tabulated unit stress in bending (Article 13.6.4.1) allowable unit stress in bending (Article

In calculating live load stresses in wood, impact shall be neglected unless otherwise noted. See Article 3.8.1. 13.1.4

volume factor for glued laminated timber with

beam stability factor (Article 13.6.4.4) wet service factor (Article 13 I) column stability factor (Article 13.7.3.3)

F.

=

Fg

=

(Article 13.7.3.1) tabulated unit stress in compression perpendicular to grain (Article 13.6.6.2) allowable unit stress in compression perpendicular to grain (Article 13.6.6.2) tabulated unit stress in bearing parallel to grain (Article 13.7.4.1)

=

allowable unit stress in bearing parallel to grain (Article 13.7.4.1)

315

316 F,

HIGHWAY BRIDGES =

=

F,

=

tabulated unit stress in tension parallel to grain (Article 13.8.1) allowable unit stress in tension parallel to grain (Article 13.8.1) tabulated unit stress in shear parallel to grain (Article 13.6.5.3)

F,’

=

=

F

0.

=

K

=

allowable unit stress in shear parallel to grain (Article 13.6.5.3) actual unit stress in shear parallel to grain (Article 13.6.5.2) allowable unit stress for bearing on an inclined surface (Article 13.6.7)

column

effective

length

factor

13.2.1.2 13.2.1.2.1

Dimensions Structural calculations for sawn lumber

shall be based on the net dimensions of the member for the anticipated use conditions. These net dimensions depend on the type of surfacing, whether dressed, roughsawn or full-sawn.

13.2.1.2.2 For dressed lumber, the net dry dimensions given in Table 13.2.IA shall be used for design, regardless of the moisture content at the time of manufacture or in use.

(Article

13.7.3.3.3) KbE

13.1.4

=

material factor for beam stability (Article

=

material factor for column stability (Article

13 .6.4.4.5)

13.2.1.2.3 Where the design is based on rough, fullsawn or special sizes, the applicable moisture content and dimensions used in design shall be noted in the plans and specifications.

13.7.3.3.5)

L

=

=

4, 4

= =

Net Dry Dimensions for Dressed Lumber

TABLE 13.2.lA

length of bending member between points of zero moment (Article 13.6.4.3) actual column length between points of lateral support (Article 13.7.3.3.3)

length of bearing (Article 13.6.6.3) effective bending member length (Article

Nominal Thickness

Dry Thickness

Dimension Lumber (inches): 2 1-1/2

Nominal Width

Dry Width

2

1-1/2

2-1/2

2

3

2-1/2

3 3-1/2

2-1/2 3

4

3-1/2

13.6.4.4.3)

4

3-1/2

=

bending member slenderness ratio (Article

4-1/2

4

V

=

vertical shear (Article 13.6.5.2)

5 6 8 10 12

4-1/2 5-1/2 7-1/4 9-1/4 11-1/4

VLt)

=

maximum vertical shear at

14

13-114

16

15-1/4

4

=

1,,

=

13.6.4.4.3) effective column length (Article 13.7.3.3.3) unsupported bending member length (Article

13.6.4.4.4)

3d

or L/4 due to

wheel loads distributed laterally as specified for

moment (Article 13.6.5.2) V1~

=

Vie

=

distributed live load vertical shear (Article 13.6.5.2) maximum vertical shear at 3d or L/4 due

x

=

to undistributed wheel loads (Article 13.6.5.2) species variable for computing the volume factor (Article 13.6.4.3)

angle between the direction of load and the rection of grain (Article 13.6.7)

8

=

13.2

MATERIALS

13.2.1

di-

Beams and Stringers and Posts and Timbers (inches): 5 and 1/2 less 5 and greater than greater

nominal 13.2.2

1/2 less than nominal

Glued Laminated Timber

132.2.1

General

Glued laminated timber shall comply with the requirements of AASHTO M 168 and shall be manufactured using wet-use adhesives.

Sawn Lumber 13.2.2.2

13.2.1.1

Dimensions

General

Sawn lumber shall comply with the requirements of AASHTOM 168.

13.2.2.2.1 Structural calculations for glued laminated timber shall be based on the net finished dimensmons.

13.2.2.2.2

DIVISION I—DESIGN

13.2.2.2.2 For Western Species and Southern Pine, the standard net finished widths shall be as given in Table 13.2.2A. Other, nonstandard finished widths may be used subject to design requirements.

TABLE 13.2.2A Standard Net Finished Widths of Glued Laminated Timber Manufactured from Western Species or Southern Pine Nominal Width (in.)

Western Species Net Finished Width (in.)

Southern Pine Net Finished Width (in.)

4 6 8

3-1/8 5-1/8 6-3/4 8-3/4

3 5 6-3/4 8-1/2

10-3/4 12-1/4 14-1/4

10-1/2

10 12 14 16

13.2.3

12

14

Structural Composite Lumiber

13.2.3.1

General

Structural composite lumber, including laminated veneer lumber and parallel strand lumber, shall comply with the requirements of ASTM D 5456 and shall be manufactured using wet-use adhesives which comply with requirements of ASTM D 2559. 13.2.3.2

Laminated Veneer Lumber

13.3 13.3.1

317

PRESERVATIVE TREATMENT Requirement for Treatment

All wood used for structural purposes in exposed permanent applications shall be pressure impregnated with wood preservative in accordance with the requirements of AASHTO M 133.

13.3.2

Treatment Chemicals

All structural members that are not subject to direct pedestrian contact shall preferably be treated with oil-type preservatives. Members that are subject to direct pedestrian contact, such as rails and footpaths, shall be treated with waterborne preservatives oroilborne preservatives in light petroleum solvent. Direct pedestrian contact is considered to be contact which may be made while the pedestrian is situated anywhere in the access route provided for pedestrian traffic. 13.3.3

Field Treating

Insofar as is practicable, all wood members shall be designed to be cut, drilled, and otherwise fabricated prior to pressure treatment with wood preservatives. When cutting, boring, or other fabrication is necessary after preservative treatment, exposed, untreated wood shall be specified to be field treated in accordance with the requirements ofAASHTOM 133.

Laminated veneer lumber shall consist of a composite

of wood veneer sheet elements with wood fibers oriented primarily along the length of the member. Veneer thickness shall not exceed 0.25 inches. 13.23.3

Parallel Strand Lumber

Parallel strand lumber shall consist of wood strand elements with wood fibers oriented primarily along the length of the member. The least dimension at the strands

shall not exceed 0.25 inches and the average length shall be a minimum of 150 times the least dimension. 132.3.4

Dimensions

Structural calculations for structural composite lumber

13.3.4

Fire Retardant Treatments

Fire-retardant chemicals shall not be used unless it is demonstrated that they are compatible with the preservative treatment. When fire retardants are used, design values shall be reduced by the strength and stiffness reduction factors specified by the fire retardant chemical manufacturer.

13.4

DEFLECTION

13.4.1 The term “deflection” as used herein shall be the deflection computed in accordance with the assumptions

shall be based on the net finished dimensions.

made for loading when computing stress in the members.

13.2.4

13.4.2 Flexural members of bridge structures shall be designed to have adequate stiffness to limit deflections or any deformations that may adversely affect the strength or serviceability of the structure.

Piles

Wood piles shall comply with the requirements of AASHTOM 168.

318

HIGHWAY BRIDGES

13.4.3

13.4.3 Members having simple or continuous spans preferably should be designed so that the deflection due to service live load does not exceed 7s~ of the span.

are graded to Beam and Stringer grade requirements, the

13.4.4 For timber deck structures with timber girders or stringers of equal stiffness, and cross-bracing or diaphragms sufficient in depth and strength to ensure lateral distribution of loads, the deflection may be computed by considering all girders or stringers as acting together and having equal deflection. When the cross-bracing or di-

13.5.2.2.4 Beam and Stringer grades are normally graded for use as a single, simple span. When used as a continuous beam, the grading provisions customarily applied to the middle third of the simple span length shall be applied to the middle two-thirds of the length for two-span beams, and to the entire length for beams continuous over three or more spans.

aphragms are not sufficient to laterally distribute loads,

tabulated unit bending stress for the applicable Beam and

Stringer grades may be used.

deflection shall be distributed as specified for moment. 13.5.3 134.5

For concrete decks on wood girders or stringers, the deflection shall be assumed to be resisted by all beams or stringers equally. 13.5

13.5.1

DESIGN VALUES General

Stress and modulus of elasticity values used for design,

referred to as allowable design values, shall be the tabulated values modified by all applicable adjustments required by this Section. The actual stress due to loading

shall not exceed the allowable stress. 13.5.2

Tabulated Values for Sawn Lumber

Tabulated Values for Glued Laminated Timber

13.5.3.1 Tabulated values for glued laminated timber of softwood species are given in Tables I 3.5.3A and

13.5.3B. Values for bearing parallel to grain are given in Table 13.5.2A. These values are taken from the 1987

Edition of the American Institute of Timber Construction, AITC 117-87 Design, “Standard Specifications for Structural

Glued Laminated Timber of Softwood

Species.” Refer to AITC 117-87 Design for a more complete listing.

13.5.3.2 Tabulated values for hardwood species shall be as given in the 1985 Edition of American Institute of Timber Construction,AITC 119, “Standard Specifications for Hardwood Glued Laminated Timber.”

13.5.2.1 Tabulated values for sawn lumber are given in Table 13.5.IA for visually graded lumber and Table 13.5.1 B for mechanically graded lumber. Values forbearing parallel to grain are given in Table I 3.5.2A. These val-

13.5.3.3 Species other than those specifically included orreferenced in this Section may be used, provided that tabulated values are established for each species in accordance with AASHTO M 168.

ues are taken from the 1991 Edition of the NDS® and represent a partial listing of available species and grades. Refer to the 1991 Edition of the NDS® for a more complete listing.

13.5.4

13.5.2.2

Stress Grades in Flexure

13.5.2.2.1 The tabulated unit bending stress for Dimension (2 to 4 inches thick) and Post and Timber grades applies to material with the load applied either to the narrow or wide face.

Tabulated Values for Structural Composite Lumber

135.4A Representative tabulated design values for structural composite lumber are given in Table 13.5.4A for laminated veneer lumber and Table I 3.5.4B for parallel strand lumber. 13.5.5

Adjustments to Tabulated Design Values

13.5.5.1 13.5.2.2.2 The tabulated unit bending stress for Decking grades applies only when the load is applied to the wide face.

13.5.5.1.1

Wet Service Factor, CM Tabulated values for sawn lumber assume

that the material is installed and used under continuously

The tabulated unit bending stress for

dry conditions where the moisture content of the wood does not exceed 19 percent. When the moisture content at

Beam and Stringer grades applies only when the load is applied to the narrow face. When Post and Timber sizes

tabulated values shall be reduced by the wet service fac-

13.5.2.2.3

installation or tn service is expected to exceed 19 percent,

13.5.5.1.1

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HIGHWAY BRIDGES

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13.5.5.1.1

HIGHWAY BRIDGES

326

TABLE 13.5.IB Tabulated Design Values for Mechanically Graded Dimension Lumber Design Values in Pounds per Square Inch (psi)

Species and Commercial Grade

Size Classification

Tension Compression Modulus Parallel Parallel of Bending to Grain to Grain Elasticity Fb F, FA E

Grading Rules Agency

MACHINE STRESS RATED (MSR) LUMBER 900f-1.OE 1200f-1.2E 1350f-1.3E 1450f-1.3E 1500f-1.3E 1500f-l.4E 1650f-1.4E 1650f-1.5E 1800f-1.6E 1950f-1.SE 1950f-1.7E 2100f-1.8E 2250f-1.6E 2250f-1.9E 2400f-1.7E 2400f-2.OE 2550f-2.1E 2700f-2.2E 2850f-2.3E 3000f-2.4E 3150f-2.SE 3300f-2.6E 900f-1 .2E 1200f-1.SE 1350f-1.8E 1500f-1.8E 1800f-2.1E

2” & less in thickness 2” & wider

2~I & less in thickness 6” & wider

900 1200 1350 1450 1500 1500 1650 1650 1800 1950 1950 2100 2250 2250 2400 2400 2550 2700 2850 3000 3150 3300

350 600 750 800 900 900 1020 1020 1175 1375 1375 1575 1750 1750 1925 1925 2060 2150 2300 2400 2500 2650

1050 14(10 1600 1625 1650 1650 1700 1700 1750 1800 1800 1875 1925 1925 1975 1975 2025 2100 2150 2200 2250 2325

1,000,000 1,200,000 1,300,000 1,300,000 1,300,000 1,400,000 1,400,000 1,500,000 1,600,000 1,500,000 1,700,000 1,800,000 1,600,000 1,900,000 1,700,000 2,000,000 2,100,000 2,200,000 2,300,000 2,400,000 2,500,000 2,600,000

WCLIB, WWPA NLGA, SPIB, WCLIB, WWPA SPIB, WCLIB, WWPA NLGA, WCLIB, WWPA SPIB NLGA,SPIB,WCLIB,WWPA SPIB NLGA, SPIB, WCLIB, WWPA NLGA, SPIB, WCLIB, WWPA SPIB NLGA, SPIB, WWPA NLGA, SPIB, WCLIB, WWPA SPIB NLGA, SPIB, WWPA SPIB NLGA, SPIB, WCLIB, WWPA NLGA, SPIB, WWPA NLGA, SPIB, WCLIB, WWPA SPIB, WWPA NLGA, SPIB SPIB SPIB

900 1200 1350 1500 1800

350 600 750 900 1175

1050 1400 1600 1650 1750

1,200,000 1,500,000 1,800,000 1,800,000 2,100,000

NLGA, WCLIB NLGA, WCLIB NLGA WCLIB NLGA, WCLIB

1. Design values are taken from the 1991 Edition of the NDS and are for a 10-year load duration and dry service conditions. Refer to the 1991 NDS for additional grades and for a summary of grading rules agencies. 2. Design values for shear parallel to grain and compression perpendicular to grain shall be as specified in Table 13.5.1A forNo.2 visually graded dimension lumber of the appropriate species. 3. Use of the wet service factor, shear stress factor, repetitive member factor, and flat use factor shall be as specified in Table 13.5. lA

for visually graded dimension lumber.

tors. CM, given in footnotes to Tables 13.5.IA and 13.5.lB.

bles I 3.5.4A and I 3.5.4B for structural composite lumber.

13.5.5.1.2 Tabulated values for glued laminated timher and structural composite lumber assume that the material is used under continuously dry conditions where the moisture content in service does not exceed 16 percent.

13.5.5.1.3 The moisture content of wood used in cxposed bridge applications will normally exceed 19 percent and tabulated values shall be reduced by the wet service factor unless an analysis of regional, geographic, and climatological conditions that affect moisture content indi-

When the moisture content in service is expected to exceed 16 percent, tabulated values shall be reduced by the wet service factors, C~

1, given in the footnotes to Tables 13.5.3A and 13.5.3B for glued laminated timber and Ta-

cate that the in-service moisture content will not exceed 19 percent for sawn lumber and 16 percent for glued laminated timber and structural composite lumber over the life of the structure.

13.5.5.2

327

DIVISION I—DESIGN TABLE 13.5.2A

Tabulated Design Values for Bearing Parallel to Grain

Dry Service Conditions Sawn Lumber Species Combination

Wet Service Conditions

5” x 5” & Larger

2” and 4” Thick

Glued Laminated Timber

1570 1350 880 1110 1270 1150 1100 1010 1320 1540 940 810 890

1730 1480 — 1220 1390 1270 1210 1110 1450 1690 1040 900 —

2360 2020 1340 1670 1900 1730 1650 1520 1970 2310 1410 1220 1340

2750 2360

Douglas Fir-Larch (Dense) Douglas Fir-Larch Eastern Softwoods Hem-Fir Mixed Southern Pine Northern Red Oak Red Maple Red Oak Southern Pine Southern Pine (Dense) Spruce-Pine-Fir Spruce-Pine-Fir (South) Yellow Poplar

1940 2010 1930 1770 2300 2690 1650 1430 1560

1. Design values are taken from the 1991 Edition of the NDS. Refer to the 1991 NDS for additional species. 2. Wet and dry service conditions are as defined in Article 13.5.4.1. The wet service factor has been applied to values tabulated for wet service conditions and further adjustment by this factor is not required.

13.5.5.2

Load Duration Factor, Cm)

13.5.5.2. 1 Wood can sustain substantially greater maximum loads for short load durations than for long load durations. Tabulated stresses for sawn lumber, glued lainmated timber, and structural composite lumber are based on a normal load duration which contemplates that the member is stressed to the maximum stress level, either continuously or cumulatively, for a period of approximately 10 years, andlor stressed to 90 percent of the maximum design level continuously for the remainder of the member life. 13.5.5.2.2 When the full maximum load is applied either cumulatively or continuously for periods other than 10 years, tabulated stresses shall be multiplied by the load duration factor, C1), given in Table I 3.5.5A. 13.5.5.2.3 The provisions of this article do not apply to modulus of elasticity or to compression perpendicular to grain, but do apply to mechanical fastenings, except as otherwise noted. The load duration factor for impact does

not apply to members pressure-impregnated with preservative salts to the heavy retentions required for marine exposure. 13.5.5.2.4 from

Increases in tabulated stresses resulting

various load duration factors are not cumulative and

the load duration factor tor the shortest duration load in a

combination of loads shall apply for that load combination. The resulting structural members shall not be smaller than required for a longer duration of loading (refer to the 1991 Edition of the NDS~ for additional commentary). 13.5.5.2.5 Modification of design stresses for load combinations, as specified in Section 3, are cumulative with load duration adjustments.

13.5.5.3

Adjustment for Preservative Treatment

Tabulated values apply to untreated wood and to wood that is preservatively treated in accordance with the requirements ofAASHTO M 133. Unless otherwise noted, no adjustment of tabulated values is required for preservative treatment. 13.6 13.6.1

BENDING MEMBERS

General

13.6.1.1

The provisions of this article are applicable

to straight members and to slightly curved bending members where the radius of curvature exceed the span in inches divided by 800. Additional design requirements for

HIGHWAY BRIDGES

328

13.6.1.1

00

0.

Eo.a~‘-~.u -~~a

~

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.00.

‘0 0 0

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~

~

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+

, for total load

h~ ) ~c.t.L , for live load

Fsr

thickness shall be increased by a factor: 2 x gross width

GS/f~i — 2.0LOT,

1+

l.5(h~, >

where F~r is the allowable stress range based on fatigue loading. F,, shall be taken from Table 10.3.1 A of Division I of this specification using category A for a Nonredundant Load Path Structure. If holes exist, the minimum

~1c.TL <

net width

4A~

where 0Tr. is the total rotation about the transverse axis of the bearing, including the effects of initial lack of parallelism, creep, shrinkage, and temperature. Reduced stress levels for rotations about the longitudinal axis of the bearing shall be computed by a rational method.

Stability

The bearings shall be proportioned to prevent stability failure. The average compressive stress due to total dead and live load on rectangular bearings shall satisfy:

Rotation and Combined Compression and Rotation

The rotational deformations about each axis shall be taken as the maximum possible rotation between the top and bottom of the bearing caused by initial lack of parallelism and girder end rotation. They shall be limited

and

347

14.5

ANCHORAGE

If the design shear force, I-I, due to bearing deformation exceeds one-fifth of the compressive force P due to dead load alone, the bearing shall be secured against horizontal movement. The bearing shall not be permitted to sustain uplift forces.

14.6

HIGHWAY BRIDGES

348 14.6

DESIGN FORCES FOR SUPPORTING

14.7

STRUCTURE The forces imposed by the bearing on the substructure are a function of the stiffness of the bearing and the flexibility of the substructure. Maximum forces to be applied by the bearing (for a rigid substructure) may be computed in accordance with Article 14.6.1 for shear and in accordance with Article 14.6.2 for moment.

STIFFENERS FOR STEEL BEAMS AND GIRDERS

The flanges of steel members seated on elastomeric bearings must be flexurally stiff enough not to risk damage to the bearing. Any necessary stiffening may be accomplished by means of a sole plate or vertical stiffeners. The stiffening requirements of this section do not replace

any others in this specification, but should be read in conjunction with them.

Single-webbed beams and girders symmetric about 14.6.1

Shear Force

their minor (vertical) axis and placed symmetrically on

the bearing need no additional stiffening if: If a positive slip apparatus is installed, H shall be taken

as the largest force which can be transmitted by the apparatus. If no positive slip apparatus is installed, the design shear force shall be taken as not less than H = G A ~h/hfl, where ~,, is the horizontal movement of the bridge superstructure relative to conditions when the bearing is undeformed and G is the shear modulus of the elastomer at 0F. In bearings in which the elastomer is specified by its 73

hardness, the value of G used shall be the highest value of the range given in Table 14.3.1.

bf< 2tf

Moment

The moment induced by bending of a rectangular bearing about an axis parallel to its long side shall be taken as not less than M = (0.5 E~) I OTL.X/h~, where

I

=

WLV12.

G~

where b 1 = total flange width, t~ = thickness of flange or combined flange and sole plate, and F,g = yield stress of the girder steel. 14.8

14.6.2

Fyg 3.4

PROVISIONS FOR INSTALLATION EFFECTS

Allowance shall be made during design for misalignment in bridge girders due to fabrication and erection tolerance, camber, and other sources. The bearings shall be located and installed in such a way as to permit subsequent replacement.

Section 15 TFE BEARING SURFACE 151

GENERAL

Unfilled or filled TFE

15.1.1 Proprietary makes of polytetrafluoroethylene (TFE) fixed and expansion bearings may be used if in the opinion of the Engineer’. and substantiated either by tests or experience, they meet design requirements.

Fabric containing TFE fibers

¼~in. minimum to 12 in. maximum

V~, in. minimum to

1,, in.

maximum

15.1.2 Bearings having sliding surfaces of TFE shall be subject to the requirements of this Section and to Sections applicable to the particular types of construction with which they are used.

Interlocked Bronze and Filled TFE Structures

15.1.3

TFE-Perforated Metal Composite

The TFE material consisting of filled or unfilled sheet, fabric containing TFE fibers, interlocked bronze and filled TFE structures, TFE-perforated metal composites together with adhesive materials, stainless steel mating surface and manufacturing processes shall conform to the requirements given in Article 18.8—

/2

in. minimum to 1,, in. maximum

1,, in. minimum to 1, in. maximum

15.2.4 The TFE sliding surface must be either bonded under factory controlled conditions or mechanically con-

Division II.

nected to a rigid back-up material capable of resisting any bending stresses to which the sliding surfaces may be subjected. Alternatively, TFE material of twice the thickness specified above may be recessed for half its thickness in the back-up material and shall not be less than i~ in. thick. Ifthe other side of the back-up material is to be bonded to an elastomeric pad, the back-up material must have suffi-

15.2 DESIGN 15.2.1 TFE sliding surfaces are designed to translate or rotate by sliding of a self-lubricating polytetrafluoroethylene surface across a smooth hard mating surface prefer-

cient tensile strength to restrain the elastomeric pad. The elastomeric pad must be sufficiently hard to allow sliding of the contact surfaces, preferably at least 70 durometer hardness.

ably of stainless steel or other equally corrosion resistant material. 15.2.2 Expansion hearings having sliding surfaces of TFE shall not be used without provision for rotation,

15.2.5 The mating surface to the TFE should be an accurate flat, cylindrical, or spherical surface as required

which shall be not less than 0.015 radians, to prevent excessive local stresses on the TFE sliding surface. Rotation shall be considered the sum of live load rotation, changes

by the design and shall have minimum Brinell hard-

ness of 125 and a surface finish of less than 20-microinches

in camber during construction, and misalignment of the

root mean square (rms). The mating surface shall completely cover the TFE surface in all operating positions of

bearing seats due to construction tolerances. The design shall include compensating provision for grade. Provision

the bearing. Wherever possible, the mating surface shall be

for rotation may be accomplished with a hinge, radiused

oriented so that sliding movements will cause dirt and dust

sliding surfaces, elastomeric pads, pre-formed fabric pads, or other means.

accumulation to fall from the mating surface.

15.2.3

15.2.6 The minimum coefficient of friction used fbr design shall he as specified by the bearing manufacturer or as shown on the next page.

TFF sliding surfaces shall have the following

minimum and maximum thickness: 349

HIGHWAY BRIDGES

350 Material

Bearing Pressure 500 psi

2,000 psi 3,500 psi

Unfilled TFE, Fabric containing TFE fibers, TFE-Perforated Metal Composite

.08

.06

.04

Filled TUE

.12

.10

.08

Interlocked Bronze and Filled TFE Structures

.10

.07

.05

Interlocked Bronze and Filled TUE Structures TFE-Perforated Metal Composite

3,500 psi 3,500 psi 2,000 psi 3,500

Unfilled and Filled TFE Fabric containing TFE fibers Interlocked Bronze and Filled

10,000 psi

5,000 psi

TFE Structures TFE-Perforated Metal Composite

10,000 psi 5,000 psi

152.9 Holes or slots shall not be used in the sliding surfaces.

15.2.7 The average bearing pressure on the TUE sliding surface due to all loads shall not exceed: Filled TFE Unfilled TFE (Recessed) Unfilled TUE (Not Recessed) Fabric containing TFE fibers

15.2.6

psi

6,000 psi 5,000 ~

15.2.10 Welding to steel plate that has a bonded TFE surface may be permitted providing welding procedures are established which restrict the maximum temperature

reached by the bond area to less than 3000F (I 500C) as determined by temperature indicating wax pencils or other suitable means.

15.2.11 Means shall be provided in the design to locate positively all elements of the bearing. Where a thin noncorrosive smooth facing material is used as a mating sliding surface, it shall be structurally bonded by an approved adhesive system and may also be mechanically fastened by means of either screws or rivets to the back-up mater-

15.2.8

The edge load pressure due to all loads and rota-

tion shall not exceed:

ial, or if the materials permit, seal-welded around the entire perimeter of the facing material.

Section 16 STEEL TUNNEL LINER PLATES 16.1

16.1.1

GENERAL AND NOTATIONS

critical pipe diameter (Article 16.3.4) modulus of elasticity (Article 16.3.3) factor of safety for buckling (Article 16.3.4) buckling stress (Article 16.3.4) minimum specified tensile strength (Article

=

E FS

General

= = =

16.1.1.1

These criteria cover the design of coldformed panel steel tunnel liner plates. The minimum thickness shall be as determined by design in accordance with Articles 16.2, 3, 4, 5, and 6 and the construction shall

=

H

16.3.4) height of soil over the top of the tunnel (Article 16.2.4)

=

conform to Section 26—Division II. The supporting capacity of a nonrigid tunnel lining such as a steel liner plate results from its ability to deflect under load, so that side

I k

restraint developed by the lateral resistance of the soil constrains further deflection. Deflection thus tends to

P

=

Pd

=

moment of inertia (Article 16.3.3) parameter dependent on the value of the friction angle (Article 16.3.4) external load on tunnel liner (Article 16.2.1) vertical load at the level of the top of the tunnel liner due to dead load (Article 16.2. I)

= =

equalize radial pressures and to load the tunnel liner as a compression ring.

16J.1.2

vertical load at the level of the top of the tunnel

=

The load to be carried by the tunnel liner is

a function of the type of soil. In a granular soil, with little or no cohesion, the load is a function of the angle of internal friction of the soil and the diameter of the tunnel being constructed. In cohesive soils such as clays and silty clays the load to be carried by the tunnel liner is dependent on the shearing strength of the soil above the roof of

r T W

=

liner due to live load (Article 16.2.1) radius of gyration (Article 16.3.4) thrust per unit length (Article 16.3.4) total (moist) unit weight of soil (Article

0

=

friction angle of soil (Article 16.3.4.1)

= =

16.2.4)

16.1

the tunnel.

LOADS

162.1 External load on a circular tunnel liner made up of tunnel liner plates may be predicted by various methods including actual tests. In cases where more precise

16.1.1.3 A subsurface exploration program and appropriate soil tests should be performed at each installation before undertaking a design.

methods of analysis are not employed, the external load P

can be predicted by the following:

16.1.1.4 Nothing included in this section shall be interpreted as prohibiting the use of new developments

(a) If the grouting pressure is greater than the computed external load, the external load P on the tunnel

where usefulness can be substantiated.

liner shall be the grouting pressure.

16.1.2

(b) In general the external load can be computed by the formula:

Notations

A

=

Cd

=

D

=

D

=

cross-sectional area of liner plates (Article 16.3.4) coefficient for tunnel liner, used in Marston’s

P

=

P +

Pd

(16-I)

where:

formula (Article 16.2.4) horizontal diameteror span of the tunnel (Article 16.2.4) pipe diameter (Article 16.3.3) 351

P

=

P,

=

the external load on the tunnel liner; the vertical load at the level of the top of the tunnel liner due to live loads;

HIGHWAY BRIDGES

352 =

the vertical load at the level of the top of the tunnel liner due to dead load.

16.3

DESIGN

16.3.1 16.2.2 For an H 20 load, values of P, are approximately the following: H(ft) P,(lbpersqft)

4 375

5 6 7 260 190 140

8 9 110 90

10 75

16.2.3 Values of Pd may be calculated using Marston’s formula for load or any other suitable method. 16.2.4 In the absence of adequate borings and soil tests, the full overburden height should be the basis for ~d in the tunnel liner plate design. The following is one form of Marston’s formula: =

(16-2)

CdWD

16.2.1

Criteria

The following criteria must be considered in the design of liner plates: (a) (b) (c) (d)

Joint strength. Minimum stiffness for installation. Critical buckling of liner plate wall. Deflection or flattening of tunnel section.

16.3.2

Joint Strength

16.3.2.1 The seam strength of liner plates must be sufficient to withstand the thrust developed from the total load supported by the liner plate. This thrust, T, in pounds

per linear foot is:

where: Cd

W D H

= = = =

coefficient for tunnel liner, Figure 16.2.3A; total (moist) unit weight of soil; horizontal diameter or span of the tunnel; height of soil over the top of the tunnel.

T where P

=

=

PD/2

load as defined in Article 16.2, and D

diameter or span in feet.

12

C Cs 0. CO

0 C 0)

n

.0 ‘I) 0

0 0 Cs

0 I 0 (I)

‘I) Cs

Values of coefficient Cd

FIGURE 16.2.3A.

(16-3)

Diagram for Coefficient Cd for Tunnels in Soil (~

Friction Angle)

=

16.3.2.2

353

DIVISION I—DESIGN

16.3.2.2 The ultimate design longitudinal seam strengths are:

For diameters less than D~, the ring compression stress at which buckling becomes critical is:

TABLE 16.3.2.2 Ultimate Seam Strength of Liner Plates Plate Thickness Ultimate Strength, (in.) (kips/fi) 2 Flange 4 Flange 0.075 0.105 0.135 0.164 0.179

20.0 30.0 47.0 55.0 62.0

26.0 43.0 50.0 54.0

0.209

87.0

67.0

0.239 0.313

92.0

81.0 115.0

0.375

119.0

1 2E =

(kD/r)2

=

(r/k) 24E/f, = critical pipe (16-7) diameters in inches; minimum specified tensile strength in pounds per

square inch; f~= buckling stress in pounds per square inch, not to

exceed minimum specified yield strength; D

=

r

=

E

=

pipe diameter in inches; radius of gyration of section in inches per foot; modulus of elasticity in pounds per square inch.

k will vary from 0.22 for soils with ~> K 15.

16.33.1 The liner plate ring shall have enough rigidity to resist the unbalanced loads of normal construction: grouting pressure, local slough-ins, and miscellaneous concentrated loads. The minimum stiffness required for these loads can be

soils 4

expressed for convenience by the formula below. It must

plate divided by the factor of safety.

T= f~A FS

require higher values (greater effective stiffness). Final de-

Minimum stiffness

=

EI/D2

15 to 0.44 for

16.3.4.2 Design for buckling is accomplished by limiting the ring compression thrust T to the buckling stress multiplied by the effective cross-sectional area of the liner

be recognized, however, that the limiting values given here are only recommended minima. Actual job conditions may

16.3.3.2 The minimum stiffness for installation is determined by the formula:

(16-6)

inpsi

where:

Minimum Stiffness for Installation

termination on this factor should be based on intimate knowledge of the project and practical experience.

(16-5) psi

For diameters greater than D~:

=

16.3.2.3 The thrust, T, multiplied by the safety factor, should not exceed the ultimate seam strength. 16.3.3

—

L4~E x~+2~2j in

(16-8)

where:

T A FS

=

thrust per linear foot from Article 16.3.2; effective cross-sectional area of liner plate in

=

square inches per foot; factor of safety for buckling.

=

(16-4) 16.3.5

Deflection or Flattening

where: D F

=

diameter in inches;

modulus of elasticity, psi (29 X lOb); moment of inertia, inches to the fourth power per inch; For 2-Flange (FIID2) 50 minimum; For 4-Flange (EI/D2) = Ill minimum; = =

16.3.4

Critical Buckling of Liner Plate Wall

16.3.4.1

\Vall buckling stresses are determined from

the following forminilac:

16.3.5.1 Deflection of a tunnel depends significantly on the amount of over-excavation of the bore and is affected by delay in backpacking or inadequate backpacking. The magnitude of deflection is not primarily a func-

tion of soil modulus or the liner plate properties, so cannot be computed with usual deflection formulae.

it

16.3.5.2 Where the tunnel clearances are important. the designer should oversize the structure to provide for a normal deflection. Good construction methods should resuIt in deilections of not more than 3 percent of the nor— mnal diameter.

354

16.4

HIGHWAY BRIDGES TABLE 16.5b Section Properties for Two-Flange Liner Plate

164 CHEMICAL AND MECHANICAL REQUIREMENTS

16.4.1

Chemical Composition

Base metal shall conform to ASTM A 569.

16.4.1

Minimum Mechanical Properties of Flat Plate Before Cold Forming

Tensile strength

—

Yield strength

—

Elongation, 2 inches

Thickness (in.)

Effective Area (in3/in.)

Moment of Inertia (in.4/in.)

0.075

0.096

0.034

0.105 0.135 0.164

0.135 0.174 0.213

0.049 0.064 0.079

0.179

0.233

0.087

0.209 0.239

0.272 0.312

0.103 0.118

42,000 psi

28,000 psi 30 percent

16.6

COATINGS

Steel tunnel liner plates shall be of heavier gage or

164.3 Dimensions and Tolerances

thickness or protected by coatings or other means when required for resistance to abrasion or corrosion.

Nominal plate dimensions shall provide the section properties shown in Article 16.5. Thickness tolerances shall conform to Paragraph 14 of AASHTO M 167. 16.5 SECTION PROPERTIES The section properties per inch of plate width, based on the average of one ring of linear plates, shall conform to the following: TABLE 16.5a Section Properties for Four-Flange Liner Plate Effective Area (in.2/in.)

Moment of Inertia (in.4/in.)

0.042 0.049 0.055 0.070 0.075 0.087 0.120

Thickness (in.)

Area 2/in.) (in.

12

0.105

0.133

II 10

0.1196 0.135

0.152

8 7 5 3

0.164 0.179 0.209 0.239

0.170 0.209 0.227 0.264 0.300

0.067 0.076 0.085 0.105 0.114 0.132 0.150

1/4

0.250

0.309

0.155

0.101

5/16 3/8

0.3125 0.375

0.386 0.460

0.193 0.230

0.123 0.143

Gage

16.7

BOLTS

16.7.1 Bolts and nuts used with lapped seams shall be not less than Y~ inch in diameter. The bolts shall conform to the specifications of ASTM A 449 for plate thickness equal to or greater than 0.209 inches and A 307 for plate thickness less than 0.209 inches. The nut shall conform to ASTM A 307, Grade A. 16.7.2 Circumferential seam bolts shall be A 307 or better for all plate thicknesses. 16.73 Bolts and nuts used with four flanged plates shall be not less than Y2 inch in diameter for plate thicknesses to and including 0.179 inches and not less than Y~ inch in diameter for plates of greater thickness. The bolts and nuts shall be quick acting coarse thread and shall conform to ASTM A 307, Grade A. 16.8

SAFETY FACTORS

Longitudinal test seam strength

Pipe wall buckling

—3 —2

Section 17 SOIL-REINFORCED CONCRETE STRUCTURE INTERACTION SYSTEMS 17.1

Bf,,

GENERAL

17.1.1

B,

Scope

Specifications in this Section govern the design of buried reinforced concrete structures. A buried reinforced concrete element becomes part of a composite system comprising the reinforced concrete section and the soil envelope, both of which contribute to the structural behavior of the system.

B,’ C. Cd

CA 17.1.2

Notations

A

effective tension area of concrete surrounding the flexural tension reinforcement and having the same centroid as that reinforcement, divided by the number of bars or wires, sq in.; when the flexural reinforcement consists of several bar sizes or wire the number of bars or wires shall be computed as the total area of reinforcement divided by the area of the largest bar or wire used (Articles 17.6.4 and 17.7.4) total active lateral pressure acting on pipe, lbs/ft (Article 17.4.5 and Figure 17.4C) 2/ft tension reinforcement area on width b, in.

=

A,,

=

A,

=

A,,

=

CN

=

earth load bedding factor

=

live load bedding factor

=

crack

b

=

=

=

Bd

=

Bf

=

coefficient

for

effect

of

of the vertical load and the vertical reaction (Artide 17.4.5)

C,

=

d

=

=

D

=

crack control coefficient for type of reinforcement (Article 17.4.6) distance from compression face to centroid of tension reinforcement, in. (Article 17.4.6) thickness of concrete cover measured from extreme tension fiber to center of bar or wire located closest thereto (Articles 17.6.4 and

17.7.4) D-load of pipe, three-edge bearing test load expressed in pounds per linear foot per foot of span

(Article 17.4.6) stirrup reinforcement area to resist radial ten-

= =

sion forces on width b, in.2/ft in each line of stirrups at circumferential spacing s (Article A,,

control

cover and spacing of reinforcement (Article 17.4.6) =out-to-out vertical rise of pipe, ft (Figure 17.4C) =1oad coefticient for embankment installations (Article 17.4.5) = load coefficient for trench installations (Article 17.4.4) = constant corresponding to the shape of pipe (Artide 17.4.5) = parameter which is a function of the distribution

to produce a 0.01-inch crack (Article 17.4.5) inside diameter of pipe, in. maximum service load stress in the reinforcing steel for crack control (Articles 17.6.4 and 17.7.4)

17.4.6) required area of stirrups for shear reinforcement,

=

maximum allowable strength of stirrup material. lbs/in.2 (Article 17.4.6.4.6)

in.- (Article 17.4.6.4.6.2) width of section which resists M, N, V—Usually b = 12 inches (Article 17.4.6)

f~

=specified yield strength of reinforcement, lbs/in.2 =

out-to-out horizontal span of pipe or box, ft (Artides 17.4.4. 17.4.5, 17.6.4, and 17.7.4.) horizontal width of trench at top of pipe or box, ft (Articles 17.4.4, 17.6.4, and 17.7.4.) bedding factor (Article 17.4.5)

F,,

355

=

(Article 17.4.6) factor for effect of curvature on diagonal tension (shear) strength in curved components (Article 17.4.6.4.5) factor for adjusting crack control relative to average maximum crack width of 0.01 inch when F< = 1.0 (Article 17.4.6.4.4)

356 F,,

F,,

HIGHWAY BRIDGES =

factor for crack depth effect resulting in increase

=

in diagonal tension (shear) strength with decreasing d (Article 17.4.6.4.5) soil-structure interaction factor (Articles 17.4.4,

=

17.6.4, and 17.7.4) soil structure interaction factor for embank-

=

Frp

=

F,,,

=

FN

=

=

h

=

H

=

HAF

= =

j

=

K

M

=

ment installations (Articles 17.4.4, 17.6.4, and 17.7.4) soil-structure interaction factor for trench installations (Articles 17.4.4, 17.6.4, and 17.7.4) factor for process and local materials that affect the radial tension strength of pipe (Article 17.4.6) the shear strength of pipe (Article 17.4.6.4.5) coefficient for effect of thrust on shear strength (Article 17.4.6.4.5) design compressive strength of concrete, lbs/in.(Articles 17.4.6, 17.6.2, and 17.7.2) overall thickness of member (wall thickness), in. (Article 17.4.6.4.4) height of fill above top of pipe or box, ft (Articles 17.4.4, 17.4.5, 17.6.4, and 17.7.4)

horizontal arching factor (Figure 17.4A) coefficient for effect of axial force at service load stress, f, (Article 17.4.6.4.4) coefficient for moment arm at service load stress, f, (Article 17.4.6.4.4) ratio of the active unit lateral soil pressure to unit vertical soil pressure-Rankine’s coefficient of active earth pressure (Figures I 7.4B-D) moment acting on cross section of width, b, service load conditions, in-lbs/ft (Taken as absolute 17.4.6.4.4) service load bending moment, in-lbs/ft (Article

n

=

r,,j

=

S.

=

etreumferential spacing of stirrups, in. (Article

=

5,

N,

=

N, p

=

= =

=

=

axial thrust acting on cross section of width b, service load condition (-~- when compressive, when tensile), lbs/ft (Article 17.4.6.4.4) factored axial thrust acting on cross section of

17.4.5 and 17.4.6) clear cover over reinforcement, in. (Article 17.4.6)

=

=

width b, lbs/ft (Article 17.4.6.4.6) factored shear force at critical section, lbs/ft

=

VAF w

17.4.6.4.6.1) spacing of circumferential reinforcement, in. (Article 17.4.6) internal horizontal span of pipe, in. (Articles

basic shear strength of critical section, lbs/ft where M/(V,~d) = 3.0 (Article 17.4.6) nominal shear strength provided by width b of concrete cross section, lbs/ft (Article 17.4.6) factored shear force acting on cross section of

=

= =

where M/(V~~d) = 3.0 (Article 17.4.6.4.6.2) vertical arching factor (Article 17.4.4.2.1.1) unit weight of soil, lbs per cubic foot (Article

=

17.4.4) total earth load on pipe or box, lbs/ft (Articles 17.4.4, 17.4.5, 17.6.4, and 17.7.4) fluid load in the pipe as determined according to

WL

=

Article 17.4.4.2.2, lbs/ft total live load on pipe or box, lbs/ft (Articles

WT

=

total load, earth and live, on pipe or box, lbs/ft

x

=

p

=

p

=

WE

=

17.4.4 and 17.4.5) (Articles 17.4.4 and 17.4.5)

parameter which is a function of the area of the vertical projection of the pipe over which lateral pressure is effective (Article 17.4.5) coefficient of internal friction of the soil (Figure 17.4B)

=

factored moment acting on cross section of width b, in.-lbs/ft (Article 17.4.6.4.6.1)

number of layers of reinforcement in a cage—i or2 (Article 17.4.6)

ratio of the total lateral pressure to the total vertical load (Article 17.4.5)

radius of the inside reinforcement, in. (Article 17.4.6.4.3.1) settlement ratio (Article 17.4.5.2.1)

=

17.4.6.4.4) =

=

factor for process and local materials that affect

value in design equations, always +) (Article =

q

17.1.2

p

=

=

=

coefficient of friction between backfill and trench walls (Figure 17.4B) central angle of pipe subtended by assumed distribution of external reactive force (Figure 17.4F) ratio of reinforcement area to concrete area (Artide 17.4.6) strength reduction factor for flexure (Article 17.4.6.4.1) strength reduction factors for shear and radial ten-

sion (Article 17.4.6.4.5)

width b, lbs/ft (Article 17.4.6)

17.1.3

projection ratio (Article 17.4.5.2.1) negative projection ratio (Figure 1 7.4A and Table 17.4A)

on the structure. For earth loads, see Article 3.20. For live

Loads

Design loads shall be determined by the forces acting

DIVISION I—DESIGN

17.1.3

357

loads see Articles 3.4 through 3.8 and Articles 3.11 and 3.12. For loading combinations see Article 3.22.

rials specifications may be used in lieu of service load

17.1.4

173 LOAD FACTOR DESIGN

Design

design.

Design may be based on working stress or ultimate strength principles. The design criteria shall include structural aspects (e.g. flexure, thrust, shear), handling and installation, and crack control. Footing design for cast-in-place boxes and arches shall be in conformity with Article 4.4.

systems shall be designed to have design strengths of all sections at least equal to the required strengths calculated for the factored loads as stipulated in Article 3.22, except as modified herein.

17.L5

liptical pipe, and arch pipe, the results of three edge-bear-

173.1 Soil-reinforced concrete structure interaction

17.3.2

Materials

For precast reinforced concrete circular pipe, el-

ing tests made in accordance with AASHTO materials

The materials shall conform to the AASHTO materials specifications referenced herein. 17.1.6

Soil

Structural performance is dependent on soil structure interaction. The type and anticipated behavior of the material beneath the structure, adjacent to the structure, and over the structure must be considered. 17.1.7

Abrasive or Corrosive Conditions

specifications may be used in lieu of load factor design. 17.4 17.4.1

REINFORCED CONCRETE PIPE Application

This Specification is intended for use in design for precast reinforced concrete circular pipe, elliptical pipe, and arch pipe. Standard dimensions are shown in AASHTO Material Specifications M 170, M 206, M 207, and M 242. Design wall thicknesses other than the standard wall di-

mensions may be used, provided the design complies with Where abrasive or corrosive conditions exist, suitable

all applicable requirements of Section 17.

protective measures shall be considered. 17.4.2 17.1.8

End Structures

Structures may require special consideration where erosion may occur. Skewed alignment may require special end wall designs. 17.1.9

Construction and Installation

The construction and installation shall conform to SecII.

tion 27—Division

17.2 SERVICE LOAD DESIGN 17.2.1 For soil-reinforced concrete structure interaction systems designed with reference to service loads and allowable stresses, the service load stresses shall not exceed the values shown in Article 8.15 except as modified

Materials

17.4.2.1

Concrete

Concrete shall conform to Article 8.2 except that evaluation of f may be based on cores. 17.4.2.2

Reinforcement

Reinforcement shall meet the requirements of Articles 8.3.1 through 8.3.3 only, and shall conform to one of the following AASHTO Material Specifications: M 31, M 32, M 55, M 221, or M 255. For smooth wire and smooth welded wire fabric, a yield stress of 65,000 psi and for deformed welded wire fabric, a yield stress of 70,000 psi may be used. 17.4.2.3

Concrete Cover for Reinforcement

herein.

The minimum concrete cover for the reinforcement in 17.2.2 For precast reinforced concrete circular pipe, elliptical pipe, and arch pipe, the results of three edgebearing tests made in accordance with AASHTO mate-

precast concrete pipe shall be 1 inch in pipe having a wall thickness of 2/2 inches or greater and /4 inch in pipe having a wall thickness of less than 2/2 inches.

HIGHWAY BRIDGES

358

17.4.3

Installations

17.4.3

in the Standard Installations are presented in Table

17.4C. 17.4.3.1

Standard Installations 17.4.4

presented in Figure 17.4B and Standard Trench Installations are presented in Figure 17.4C; these figures define soil areas and

Design

Standard Embankment Installations are

critical dimensions. Generic soil types, minimum compaction requirements, and minimum bedding thicknesses are listed in Table 17.4A for four Standard Embankment Installation Types and in Table 17.4B for four Standard

Trench Installation Types. 17.4.3.2

The AASHTO Soil Classifications and the USCS Soil Classifications equivalent to the generic soil types

Installation Type Type I

Type 2 (See Note 3.)

Type 3 (See Note 3.)

Type 4

General Requirements

Design shall conform to applicable sections of these specifications except as provided otherwise in this Section. For design loads, see Article 17.1.3; for standard installation, see Article 17.4.3.1; and for bedding conditions, see

Section 27, Division Il—Construction and the Soil-Structure Interaction Modifications that follow. Live loads, WL, shall be included as part of the total load, WT, and shall be

Soils

TABLE 17.4A

17.4.4.1

distributed through the earth cover as specified in Article 6.4, except that the 2-foot minimum in the first paragraph of Article 6.4 does not apply. Other methods for determmn-

Standard Embankment Installation Soils and Minimum Compaction Requirements Bedding Thickness

Haunch and Outer Bedding

Lower Side

B,/24” (600 mm) minimum, not less than 3” (75 mm). If rock foundation, use B,/12” (300 mm) minimum, not less than 6” (150 mm). B,/24” (600 mm) minimum, not less than 3” (75 mm). If rock foundation, use B /12” (300 mm) minimum, not less than 6” (150 mm).

95% SW

90% SW, 95% ML, or 100% CL

90% SW or 95% ML

85% SW, 90% ML, or 95% CL

B,/24” (600 mm) minimum, not less than 3” (75 mm). If rock foundation, use B,/12”

85% SW, 90% ML, or 95% CL

85% SW, 90% ML, or

(300 mm) minimum, not less than 6” (150 mm). No bedding required, except if rock foundation, use B,/ 12” (300 mm) minimum, not less than 6” (150 mm).

95% CL No compaction required,

No compaction required,

except if CL, use 85% CL

except if CL, use 85% CL

NOTES:

I. 2. 3. 4. 4.1 4.2 4.3

Compaciion and soil symbols -i.e. “95% SW’ refer to SW soil material with a minimum siandard proctor compaction of 95%. Sec Table 17.4C for equivalent modified proctor values. Soil in the outer bedding, haunch, and lower side zones, except within B,/3 from the pipe springline. shall be compacted to at least the same compaction as the majority of soil in the overfill zone. Only Type 2 and 3 installations are available for horizontal elliptical, vertical elliptical and arch pipe. SUBTRENCHES A subtreneh is defined as a trench with its top below finished grade by more tItan 0.1 H or. for roadways, ii~ top is at an elevation lower than 1(0.3 m) below the bottom of the pavement base material. The minimum width of a subtrench shall be 1.33 B~, or wider if requircd for adequate space to attain the specified compaction in the haunch and bedding zones. For subtrcnches with walls of natural soil, any portion of the lower side zone in the subtrench wall shall be am least as firm as an equivalent soil placed to the compaction requirements specified for the lower side zone and as firm as the majorimy of soil in the overfill lotte, or shall be removed and replaced with soil compacted to the specified level.

17.4.4.1

DIVISION I—DESIGN TABLE 17.4B

Installation Type

Standard Trench Installation Soils and Minimum Compaction Requirements Haunch and Bedding Thickness

Type I

B,/24” (600 mm) minimum, not less than 3” (75 mm). If rock foundation, use B,/ 12” (300 mm) minimum, not less than 6” (150 mm). Bj24” (600 mm) minimum, not less than 3” (75 mm). If rock foundation, use B,/12” (300 mm) minimum, not less than 6” (150 mm). B~/24” (600 mm) minimum, not less than 3” (75 mm). If rock foundation, use B.] 12”

Type 2 (See Note 3.)

Type 3 (See Note 3.)

359

Outer Bedding

Lower Side

95% SW

90% SW, 95% ML, 100% CL, or natural soils of equal firmness 85% SW, 90% ML, 95% CL, or natural soils of equal firmness 85% SW, 90% ML, 95% CL, or natural

90% SW or 95% ML 85% SW, 90% ML, or 95% CL

(300mm) minimum, not less than 6” (150 mm). Type 4

No bedding required, except if rock foundation, use B.] 12” (300mm) minimum, not less than 6” (150 mm).

soils of equal firmness No cotnpaction required, except if CL, use 85% CL

85% SW, 90% ML 95% CL, or natural soils of equal firmness

NOTES: I. 2. 3. 4. 5. 6.

Compaction and soil symbols -i.e. .95% SW-refers to SW soil material wiih minimum standard Proctor compaction of 95%. See Table 17.4C for equivalent modified Proctor values. The trench top elevation shall be no lower than 0.1 1-1 below finished grade or. for roadways, its mop shall be no lower than an elevation of I tt).3 m) below the bottom of the pavement base material. Only Type 2 and 3 installations are available for horizontal elliptical, vertical elliptical and arch pipe. Soil in bedding and haunch zones shall be compacted to at leasi the same compaction as specified for the majority ofsoil in the backfill zone. The trench width shall be wider than shown if required for adequate space to attain the specified compaction in the haunch and bedding zones. For trench walls that are within Iti degrees of vertical. the compaction or firmness of the soil in the trench walls and lower side tone need

not be considered. 7.

For trench walls with greater than 10-degree slopes that consist of embankment, the lower side shall be compacted to at least the same compaction as specified for the soil in the backfill zone.

ing total load and pressure distribution maybe used, if they are based on successful design practice or tests that reflect the appropriate design conditions.

17.4.4.2 Loads 17.4.4.2.1

Earth Loads and Pressure Distribution

The effects of soil-structure interaction shall be taken into account and shall be based on the design earth cover. sidefill compaction, and bedding characteristics of the pipe-soil installations. 17.4.4.2.1. 1

Staimdard Installations

=

F,wB,H

(17-I)

Standard Installations for both embankments and trenches shall be designed for positive projection, embankment loading conditions where F~ = VAF given, in Figure 17.4A for each Type of Standard Installation. For Standard Installations the earth pressure distribution shall be the Heger pressure distribution shown in Figure I 7.4A for each type of Standard Installation. The unit weight of soil used to calculate earth load shall be the estimated unit weight for the soils specified

for the pipe-soil installation and shall not be less than 110 lbs/cu ft.

For the Standard Installations given in 17.4.3.1. the earth load, Wi., may be determined by multiplying the prism load (weight of the column of earth) over the pipes outside diameter by the soil-structure interaction factor.

and pressure distribution shall he determined by an ap-

F,, for the specified installation type.

propriate soil-structure interaction analysis.

17.4.4.2. 1.2

Nonstandard Installations

When nonstandard installations are used, the earth load

360

17.4.4.2.2

HIGHWAY BRIDGES

TABLE 17.4C Equivalent USCS and AASHTO Soil Classifications For SIDD Soil Designations Representative Soil Types SIDD Soil GravellySand

(SW)

USCS

AASHTO

Standard Proctor

Modified Proctor

SW,SP

AI,A3

100

95

95 90

90

GW, GP

Sandy Silt (ML)

85

85 80

80 61

75 59

100

95

Also GC, SC

95

90

with less than 20% passing No. 200 sieve

90

85

85

80

80

75

49

46

100 95 90

90 85 80

85 80

75 70

45

40

100 95

90 85

90 45

80 40

GM, SM, ML

Silty Clay (CL)

GL, MH, GC, SC

CH

17.4.4.2.2

Percent Compaction

Pipe Fluid Weight

The weight of fluid, W

5 in the pipe shall be considered 3, unless

in design based on aFor fluidStandard weight Installations, of 62.4 lbs/ft the fluid otherwise specified. weight shall be supported by vertical earth pressure that

is assumed to have the same distribution over the lower part of the pipe as given in Figure 17.4A for earth load.

A2, A4

A5, A6

A7

shall be 1 foot or ~ of the diameter or rise, whichever is greater. Under rigid pavements, the distance between the top of the pipe and the bottom of the pavement slab shall be a minimum of 9 inches of compacted granular fill.

17.4.4.4 Design Methods The structural design requirements of installed precast

17.4.4.2.3

Live Loads

Live loads shall be either the AASHTO HS-Series or the AASHTO Interstate Design truck loads. Live loads shall be distributed through the earth cover as specified in Article 6.4, except that the 2-foot minimum in the first paragraph of Article 6.4 does not apply. For Standard Installations the live load on the pipe shall be assumed to

have a uniform vertical distribution across the top of the pipe and the same distribution across the bottom of the pipe as given in Figure 17.4A for earth load.

reinforced concrete pipe may be determined by either the

Indirect or Direct Method.

17.4.5

Indirect Design Method Based on Pipe Strength and Load-Carrying Capacity

17.4.5.1

Loads

The design load-carrying capacity of a reinforced concrete pipe must equal the design load determined for the

pipe as installed, or 17.4.4.3 Minimum Fill For unpaved areas and under flexible pavements, the minimum fill over precast reinforced concrete pipe

~~l21~WF

+ W~ WL ______ +

(17-2)

DIVISION I—DESIGN

17.4.5.1

361

I VAFg 4

HAF ~ — —

V

Iauaflada.T~e

A

VA?

HAP

L~ 2 3 4 ———

—————

Al

P.2

GAS

W

2.40

GAG

UG 1.45

—

—————

P.3

A4

AS

A6

a

b

C

6

0.73

LII

0.19

GAS

0.3

1.40

GAG

0.3

0.05

0.5

0.55

1.40

0.15

O.K

0.17

1.45

0.40

0.19

0.37

1.0

0.15

lAO

0.10

0.10

0.17

1.45

0.36

0.3

0.3

1.450001.450.130.110.191.450.30 — ———— ————

OZ

f

U

V

0.0

GAO

GAG

0.10

0.0

0.82

0.~

0.12

0.0

G.M

GAG

0.00— ———

0.90—

NOTES: I. VAF and HAF are vertical and horizontal arching factors. These coefficients represent nondimensional total vertical and horizontal loads on the pipe. respectively. The actual total vertical and horizontal loads are (VAF) X (PL) and (HAF) X (PL). respectively, where PL is the prism load. 2. Coefficients Al through A6 represent the integration of nondimensional vertical and horizontal components of soil pressure under the indicated portions of the component pressure diagrams (i.e., the area under the component pressure diagrams). The pressures are assumed to vary either parabolically or linearly, as shown, with the nondimensional magnitudes am goveming points represented by h, h~, oh,, vh 1, a and b. Nondimensional horizontal and vertical dimensions of component pressure regions are defined bye, d, e, uc, vd, and fcocfficients. 3. d is calculated as (0.5 c-c) his calculated as(l.5A1)/(e) (I ± u) h~ is calculated as (1.5 A2) / [(d) (I + v) + (2e)l.

FIGURE 17.4A Fleger Pressure Distribution and Arching Factors

HIGHWAY BRIDGES

362

17.4.5.1

STANDARD EMBANKMENT INSTALLATIONS

I OveriW

-

SW. ML. or CL

16 IM” )

Bc

—

Haunch — See Table 17.4A Lower Side

—

See Table 1 7.4A

U Bedd.nq —

See Table 17.4A

Ouler Bedding mater.al

and

‘~

canipac ion each side, same

~oundatsan

Mid~e Bedding loosely placed uncampacted bedding except for T~pe 4

‘e~jWenients

as haunch

FIGURE 17.4B

STANDARD TRENCH INSTALLATIONS

.uvwli

- SW. ML or Ci.

Escavatman line as requwed

Haunch — See Table 17.4B

Side — See Table 17.4B

Sed~q-See Oulw Seding metwl~ and ceinpctian each eel~ —

Faundation

reQ.n1t3

as ham~ch

FIGURE 17.4C

DIVISION I—DESIGN

17.4.5.1

363

where: D

5, B, BF.

Bfe =

=

=

expressed in pounds per linear foot per foot of diameter) to produce a 0.01-inch crack. For Type 1 installations, D-load as calculated above shall be modified by multiplying by an installation factor of I . 10; internal diameteror horizontal span of the pipe in tnches; bedding factor, see Article 17.4.5.2;

=

earth load bedding factor; live load bedding factor; WE ±WL;

=

total load on the pipe as determined according

=

BELL =

WT

D-load of the pipe (three edge-bearing test load

to Article 17.4.4; WE

=

earth load on the pipe as determined according to Article 17.4.4;

=

fluid load in the pipe as determined according

=

to 17.4.4.2.2; live load on the pipe as determined according to Article 17.4.4.

17.4.5.1.1

Ultimate D-load

The required D-load at which the pipe develops its ul-

=

CA

CN — xq

(17-3)

Values for CA and CN are listed in Table 17.4D. CA

=

CN

=

x

=

a constant corresponding to the shape of the

pipe; a parameter which is a function of the distribution of the vertical load and vertical reaction; a parameter which is a function of the area of the vertical projection of the pipe over which lateral

q

=

pressure is effective; the ratio of the total lateral pressure to the total vertical fill load.

17.4.5.2.3

Live Load Bedding Factor

The bedding factors for live load, WL, for both Circular pipe and Arch and Elliptical pipe are given in Table I 7.5F. If B,~ is less than Bfl L’ use B,, instead of B,, L for the

live load bedding factor. Design values for CA, CN, and x are found in Table 17.4D. The value of q is determined by the following equations: Arch and Horizontal Elliptical Pipe:

timate strength in a three-edge-bearing test is the design D-load (at 0.01-inch crack) multiplied by a strength factor that is specified in AASHTO materials specifications

q

=

.232.j1

+

.35pi~4~;~

(17-4)

M 170 or M 242 (ASTM C 76 or C 655) for Circular pipe, M 206 (ASTM C 506) for Arch Pipe and M 207 (ASTM C 507) for Elliptical Pipe.

17.4.5.2

Vertical Elliptical Pipe: (17-5)

Bedding Factor

The bedding factor, B,, is the ratio of the supporting strength of buried pipe to the strength of the pipe deter-

where: p

=

mnined in the three-edge-bearing test. The supporting

strength of buried pipe depends on the type of Standard Installation. See figures 17.4B and 17.4C for circular pipe and figures 17.4D and 17.4E for other arch and elliptical shapes. The tables I 7.4A and I 7.4B apply to circular, arch and elliptical shapes.

projection ratio, ratio of the vertical distance

between the outside top of the pipe and the ground or bedding surface to the outside vertical height of the pipe; 17.4.5.2.4

Intermediate Tre,mch Widths

For intermediate trench widths, the bedding factor may 17.4.5.2.1

Earth Load Bedding Factor for Circular Pipe

Earth load bedding factors, B,,, for circular pipe are presented in Table 17.4E. 17.4.5.2.2

Earth Load Bedding Factorfrr Arch and Elliptical Pipe

The bedding factor for installations of arch and elliptical pipe, Figures 17.4D and 17.4E, is:

be estimated by interpolation between the narrow trench

and transition width bedding factors. 17.4.6

Direct Design Method Based on Pressure Distribution

17.4.6.1

Loads

The total load on the pipe shall be determined according to Article 17.4.4 and Table 3.22.1 A.

364

17.4.6.1

HIGHWAY BRIDGES

—

Onerln

Sw.

O~erliIl

—

SW. ML. or Ed

Sp~ng

Bedding

—

ZI

Line

See

Table

lT4B-.j

Outer Bedding

II

llouflCh

—

See Table 1748 Lower Side — See Table 17 48

Spring Line

‘—Middle Bedding loosely placed uncompacied bedding

II

materials and

See Table 17.48—’ 0.4cr Bedding materials and compaction each side, same

Bedding

compaction each

side, some requirements as haunch

LEGEND: Ac Outside Diameter H — Backlill rooer above top of pipe

—

LEGEND: Bc = Outside Diameter H = Backfill couer ooo~e

roundatan

0ncr

top

of pipe

VERTiCAL ELLIPliCAL PIPE

HORIZONTAL ELLIPTiCAL PIPE

-

‘—Middle Bedding loosely placed uncOmpadted beading

requirements as na

roundaton

Overfill

II

SW. ML.

17.48 ~ wer Side

—

Table 1748 Bedding

LEGEND;

roundalion

Bc = Outside Diameter H — Backfill rouer abOuC

top at ppe

ARCH PIPE FIGURE 17.4D Trench Beddings, Miscellaneous Shapes The pressure distribution on the pipe from ap-

17.4.6.3

Process and Material Factors

plied loads and bedding reaction shall be determined

from a soil-structure analysis, or shall be a rational approximation. For possible pressure diagrams, see Figure

17.4F. 17.4.6.2

Strength-Reduction Factors

Strength-reduction factors for load factor design of plant made reinforced concrete pipe may be taken as 1 .0 for flexure and 0.9 for shear and radial tension. For Type I installations, the strength-reduction factor shall be 0.9 for flexure and 0.82 for shear and radial tension.

Process and material factors F~ for radial tension and

~ for shear strength for load factor design of plant made reinforced concrete pipe are conservatively taken as 1.0. Higher values may be used if substantiated by appropriate test data approved by the Engineer. 17.4.6.4 17.4.6.4.1

Reinforcement Reinforcement for Flexural Strength

A~f) sg~fd—N0 2—N~(2tt~d—h)—2MU] —

g[g(t~fd)

(17-6)

.

17.4.6.4.1

365

DIVISION I—DESIGN .s,”in~

Overfill

—

Overfill

SW. ML. or CL

Bc/B(Min.

—

SW. ML. or CL

in

1

H Ac

Bc,’B(Min.)

Bc(Mn.) Haunch

Spring Lire —~

Bc

Bc

l.lin.

Haunch — See Table 17.4A

—

See LoserTable Side t7.4A —

Spring

L,ne ~

Laser Side 1 —7.4A See Table

See Table 1 7.4A

Middle Bedding loosely placed

See Table 174A~J Bedding materials and compaction each Bc/3 side, same requirements Foundation as haunch

Bedding

—

Outer

uncompocted

LEGEND: Bc = Outside Diameter H — Backlill caoer abdue top

at

— See Table t7.4A.J “—Middle Bedding Outer Bedding loosely placed materials and Bc uncampacted bedding compaction each side. so me requireme nrs Foundation LEGEND: as haunch Bc = Outside Diameter H = Backfill caoer abouc top ot pipe Bedding

bedding

pipe

HORIZONTAL ELLIPTiCAL PIPE

Overfill

—

SW.

ML.

VERTiCAL ELUPTiCAL PIPE

or CL

Bc/6 Mm.

Bc

H Haunch — bOle I? 4A Loser Side —

~n Spi nq ii2Z\u,

See Table 17.4A Outer Bedding materials and compaction each side, same requirements as haunch

Bedding

—

See Table 17 AA

Jl Bc/3

~~Middte Bedding loosely placed uncompacted bedding ____ LEGEND: Bc = Outside Diameter H = Backfill caner abone tap of pipe

Foundation

ARCH PIPE FIGURE 17.4E Embankment Beddings, Miscellaneous Shapes

where g

=

where:

0.85 bf,~

17.4.6.4.2

h S

Minimum Rei,4~rcement

For inside face of pipe: A, = (5, -I- h)2165,000 For outside face of pipe:

(17-7)

= =

wall thickness in inches; internal diameter or horizontal span of pipe in inches.

In no case shall the minimum reinforcement be less than 0.07 square inches per linear foot. 17.4.6.4.3

A,

=

0.65 (5,

+

h)2165,000

(17-8)

For elliptical reinforcement in circular pipe and for

17.4.6.4.3.1

Maximum Flexural Reinforcement Without Stirrups Limited b-y Radial Tension

pipe 33-inch diameter and smaller with a single cage of reinforcement in the middle third of the pipe wall:

Inside A, A,

=

2 (5,

+

h)2/65,000

(17-9)

max

~

=

~

(17-10)

HIGHWAY BRIDGES

366

17.4.6.4.3.1

17.4.6.4.4

TABLE 17.4D Design Values of Parameters in

Crack Width Control

___________ Bedding Factor Equation Pipe Shape

Values

Type of

ofCA

Bedding

Values Projection ofCN

Ratio

Values of x

30,00OdA,~~ [M.

Horizontal Ellipti1.337

Type 2

0.630

—

0

C,bh2

—

fj

Type 3

0.763

0.9 0.7 0.5 0.3

0.421 0.369 0.268 0.148

where:

0.9

0.718 0.639 t).457 0.238

pressive (this may occur in pipes subject to intermittent hydrostatic pressure), use the quantity (l.IM,—0.6N,d)

Fcr

= =

N,

=

crack control factor, see Note c;

bending moment, service load; thrust (positive when compressive), service load.

If the service load thrust, N, is tensile rather than com-

Vertical Elliptical

Type 2

0.516

Type 3

0.615

0.7 1.021

0.5 0.3

(with tensile N, taken negative) in place of the quantity ([M, + N,(d h12)]Iji) in Equation (17-12). —

where:

j =

F,,,

N.jd

(17-12)

cal and

Arch

+

=

=

maximum flexural reinforcement area without stirrups in in.2/ft;

1.0 unless a higher value substantiated by test data is approved by the Engineer; radius of inches.

17.4.6.4.3.2

the

inside

reinforcement

e

—

5.5xl0~g’~fd] —0.75N

0

L (87,000+ f~) 7 =

C

in

Limited hv Concrete Compression

A max. f

where:

~0.74+0.leld; = 0.9;

(17- II)

=

0.85bf,~ and ~

1,000 =

=

tb

=

h

=

B~ and C,

=

h

N

2

1.15; clear cover over reinforcement in inches wall thickness of pipe in inches; crack control coefficients dependent on type of reinforcement used as follows:

Type Reinforcement:

bf’FO 85 —0.05 (f: —4,000)7

CL.-

eldmi.

M

C,

0.5t~s1

7

1.0

n

0.65 bf~’

TABLE 17.4E

B,

Equation (17—12) (Y)ttrifljfes on page 367.

Bedding Factors For Circular Pipe Standard Installations

Pipe Diameter, in.

Type I

Type 2

Type 3

Type 4

12

4.4

3.2

2.5

1.7

24

4.2

3.0

2.4

1.7

36

4.0

2.9

2.3

1.7

72

3.8

2.8

2.2

1.7

144

3.6

2.8

2.2

1.7

/~inQ7f.>

For pipe diameters other than listed, embankment condition bedding factors, B,. can be obtained by interpolation. Bedding factor, are based on soils being placed with the minilttulll erlolpaction specified in Tables I 7.4A and I 7.4B for each Standard lostal lation

DIVISION I—DESIGN

17.4.6.4.4 I. Smooth wire or plain bars 2. Welded smooth wire fabric, 8

1.0, the probability of a crack greater than 0.01 inch is increased.

inches maximum spacing of longitudinals 3. Welded deformed wire fabric, deformed wire, deformed bars or any reinforcement with stirrups anchored thereto.

d. Higher values for C, may be used if substantiated 1.0

by test data and approved by the Engineer.

1.5

17.4.6.4.5

1.9

=

spacing of circumferential reinforcement in inches.

section located where MIVu~,d

Notes:

Vh

a. Use n = I when the inner and the outer cages are each a single layer. Use n = 2 when the inner and the outer cages are each made up from multiple layers. b. For type 2 reinforcement having (t~sO/n > 3, also check F., using coefficients B, and C, for type 3 reinforcement, and use larger value for F0~. = 1.0, the reinforcement area, A,, will produce an average crack maximum width of 0.01 inch. For F0, values less than 1.0, the probability of a 0.01-inch crack is reduced. For F0, values greater than

=

~

Vh

=

+

3.0. 63p)

[

Fd

1

[FCF~

J

I (17-13)

=

shear strength of section where M5/V0~,d = 3.0; 1.0 unless a higher value substantiated by test

data is approved by the Engineer; p

— =

A 4,bd 0.02;

Bedding Factors, BLI, For 11S20 Live Loadings

12

24

36

48

Pipe Diameter, in. 60 72 84

0.5

2.2

1.7

1.4

1.3

1.3

1.1

1.1

1.0

2.2

2.2

1.7

1.5

1.4

1.3

1.5

2.2

2.2

2.1

1.8

1.5

2.0

2.2

2.2

2.2

2.0

2.5

2.2

2.2

2.2

3.0

2.2

2.2

3.5

2.2

4.0

FillHeight,Ft

\/i~(l.l

=

where:

c. When For

TABLE 17.4F

Shear Strength

The area of reinforcement, A,, determined in Article 17.4.6.4.1 or 17.4.6.4.4 must be checked for shear strength adequacy, so that the basic shear strength, V5, is greater than the factored shear force, V00, at the critical

where: 5,

367

96

108

120

144

1.3

1.1 1.3

1.1 1.1

1.1 1.1

1.1 1.1

1.4

1.4

1.3

1.3

1.3

1.1

1.8

1.5

1.5

1.4

1.4

1.3

1.3

2.2

2.0

1.8

1.7

1.5

1.4

1.4

1.3

2.2

2.2

2.2

2.2

1.8

1.7

1.5

1.5

1.4

2.2

2.2

2.2

2.2

2.2

1.9

1.8

1.7

1.5

1.4

2.2

2.2

2.2

2.2

2.2

2.2

2.1

1.9

1.8

1.7

1.5

4.5

2.2

2.2

2.2

2.2

2.2

2.2

2.2

2.0

1.9

1.8

1.7

5.0

2.2

2.2

2.2

2.2

2.2

2.2

2.2

2.2

2.0

1.9

1.8

5.5

2.2

2.2

2.2

2.2

2.2

2.2

2.2

2.2

2.2

2.0

1.9

6.()

2.2

2.2

2.2

2.2

2.2

2.2

2.2

2.2

2.2

2.1

2.0

6.5

2.2

2.2

2.2

2.2

2.2

2.2

2.2

2.2

2.2

2.2

2.2

NOTE:

For pipe diameters (liher than listed, B1 values can be obtained by interpolation.

HIGHWAY BRIDGES

368

17.4.6.4.4

FIGURE 17.4F Suggested Design Pressure Distribution Around a Buried Concrete Pipe for Analysis by Direct Design

ES~NTl~ F~ATtAS

~ PIPES U fl6T~LAflWi

nT-?

N / in<

N /

/

N /

/ 9e

/

5 .5

Tl)f*E.LED

TOP LW LIIBAWIfENT

IfoArivE Ptto.EcTtfJO DEAWJENT

FIGURE 17.4G Essential Features of Types of Installation.

369

DIVISION I—DESIGN

17.6.4.5

TOP OF EMBANKMENT

\~7K7KI7K77KyK~Z777\~Y77KR~77 It

a

ii I

I

:1 I~

I

Ig

I ~

‘

I

‘

H

I W,=F,,wB,H

I I. IV

I, Ii ‘IV

V

pB~

FIGURE 17.4H General Relationship of Vertical Earth Load and Lateral Pressure .~ =

F 1

=

7,000 psi; 1.6 0.8

+

17.4.6.4.6 Ed ax

=

1.25;

~xd

F.

EN

=

17.4.6.4.6.1

2r ~(+) tension tension on on the theoutside inside of of the the pipe; pipe

__ ____

=0.5—

( ) N5

6V.

+

0.25

Radial Tension Stirrups l.lS,(M5

—

0.45 N~k,d

f,r.A~d

(N5)2 ±

If V5 is less than V~, radial stirrups must be provided. See Article 17.4.6.4.6.

Radial Stirrup.s

(17-14)

where: A5,

=

required area of stirrup reinforcement for radial tension;

17.4.6.4.6

HIGHWAY BRIDGES

370

S

=

circumferential spacing of stirrups

(Sx

=

17.5

0.75f~xd); =

maximum allowable strength of stirrup material (fman = f5, or anchorage strength, whichever is less).

17.4.6.4.6.2

17.5.1

REINFORCED CONCRETE ARCH, CASTIN-PLACE Application

This specification is intended for use in the design of cast-in-place reinforced concrete arches with the arch barrel monolithic with each footing. A separate reinforced

Shear Stirrups

concrete invert may be required where the structure is sub-

1.1S5 [VaFc~4~sVci+Axr

ject to scour. (17-15)

fx,ttls.d

17.5.2

Materials

where: =

Va

=

required area of stirrups for shear reinforcement; factored shear force at section;

Mu

+1

Va~xd roan =

2(~)xbd

17.4.6.4.6.3 17.4.6.4.6.3.1

\/‘i~

Stirrup Reinft.rcement Anchorage Radial Tension Stirrup Anchorage

When stirrups are used to resist radial tension, they shall be anchored around each circumferential of the inside cage to develop the design strength of the stirrup, and

they shall also be anchored around the outside cage, or embedded sufficiently in the compression side to develop the design strength of the stirrup.72 17.4.6.4.6.3.2

Shear Stirrup Anchorage

Concrete

Concrete shall conform to Article 8.2. 17.5.2.2

4V8 =

17.5.2.1

Reinforcement

Reinforcement shall meet the requirements of Article 8.3. 17.5.3

Design

17.5.3.1

General Requirements

Design shall conform to these specifications except as provided otherwise in this Section. For design loads and loading conditions, see Article 3.2. For reinforced concrete design requirements see Section 8. 17.5.3.2

Minimum Cover

The minimum fill over reinforced concrete arches shall be 12 inches or SpanI8.

When stirrups are not required for radial tension but re-

quired for shear, their longitudinal spacing shall be such that they are anchored around each or every other tension circumferential. Such spacings shall not exceed 6 inches

(ISO mm). 17.4.6.4.6.3.3

Stirrup Enmbeddment

Other Provisions

Section 8.27. Development of Shear Reinforcement, does not apply to pipe designed according to provisions of Section 17.4.5.

Strength-Reduction Factors

Strength-reduction factors for load factor design of

cast-in-place arches may be taken as 0.90 for flexure and

Stirrups intended to resist forces in the invert and crown regions shall be anchored sufficiently in the opposite side of the pipe wall to develop the design strength of the stirrup. 17.4.6.4.6.3.4

17.5.3.3

0.85 for shear.

17.5.3.4

Splices of Reinforcement

Reinforcement shall be in conformity with Artide 8.33.1.1. If lap splicing is used, laps shall be staggered with a minimum of 1 foot measured along the circumference of the arch. Ties shall be provided connecting the intrados and extrados reinforcement. Ties shall be at 12-inch maximum spacing, in both longitudinal and circumferential directions, except as modified by shear.

17.5.3.5

Footing Design

Design shall include consideration of differential horizontal and vertical movements and footing rotations. Footing design shall conform to Article 4.4.

17.6

17.6.1

371

DIVISION I—DESIGN

17.5.3.5

REINFORCED CONCRETE BOX, CAST-IN-PLACE Application

17.6.4.2

Modification of Earth Loads for Soil Structure Interaction

The effects of soil structure interaction shall be taken into account and shall be based on the design earth cover, sidefill compaction, and bedding characteristics.. These

parameters may be determined by a soil-structure interaction analysis of the system. The loads given in Article 6.2 may be used, if they are multiplied by a soil-structure interaction factor, F0, that accounts for the type and conditions of installation as defined in Figure 17.6A, so that the total earth load, W~ on the box section is:

This specitication is intended for use in the design of cast-in-place reinforced concrete box culverts.

F0wB~H

=

(17-16)

F0 may be determined by the Marston-Spangler Theory of earth loads, as follows: 17.6.2

Materials 17.6.4.2.1

17.6.2.1

Embankment Installations

Concrete F0

Concrete shall conform to Article 8.2 except that evaluation of f may be based on test beams.

17.6.2.2

Reinforcement

=

1

-t

0.20

H B0

(17-17)

F,, need not be greater than 1.15 for installations with compacted fill at the sides of the box section, and need not be greater than 1.4 for installations with Lmncompacted till

at the sides of the box seetton. Reinforcement shall meet the requirements of Article 8.3 except that for welded wire fabric a yield strength of

17.6.4.2.2

Trench Installatiotts

65,000 psi may be used. For wire fabric, the spacing of longitudinal wires shall be a maximtmmn of 8 inches.

17.6.3

Concrete Cover for Reinforcement

The minimum concrete cover for reinforcement shall conform to Article 8.22. The top slab shall be considered

a bridge slab for concrete cover considerations.

17.6.4

Design

17.6.4.1

General Requirements

Designs shall conform to applicable sections of these specifications except as provided otherwise in this See-

F02

=

CdB3

HB,

(17-18)

Values of C~ can be obtained from Figure 17.4B for normally encountered soils. The maximum value of F6” froni weld Grade 100 or 100W .~

I

0) V

U ~

U C

6)

-

-J

L6J

~

6) ~V V 6)—

—

,~m 0.

6)=E~ :2 o

C 0

U U

C

C

6 •0 C C

V

S

0

L..

N 0l

0

0

m N (N 6) In

6)

0

5

0 ••:‘~

6)

6) 0

o

In~

0

~ .:

4

~

.,

E

~

‘3 0~

—

•~W’ ~ Orerlill

—

615

DIVISION IT—CONSTRUCTION

27.5.2.1

I

SW. ML. or CL Bc/6

U

Overl,li

-

liii ~4Haunch l....—~L......lE.z’l See Table

SW ML or Bc/6(Uin

—

Spring Line

Bedding

27.58 Side See bOle 27.58

~

See Table 27 5B~~ Outer Bedding ‘i~2ter als ~ compaction each side, same requirements at haunch —

/—

II II

27 58 Spring Line

‘~U,ddle Bedding loosely placed uncornpacted bedding

Bedding

272~~I

Table Bedding materials and compaction each side, same requwernents as haunch

LEGS NO: Bc — Outside Diameter H = Backfill corer obove 109 of pipe

Foundamion

—

—Outer See

II

— Onerl

58

“—Middle Bedd.ng loosely placed uncampocied bedding

Foundat,on

HORIZONTAL ELLIPliCAL PIPE

~Cr5dC—

LLG~NO: Be — Outside Diameter H = Backlill corer abone lop 01 pipe

VERTiCAL ELUPilCAL PIPE

~-~---~~-‘-

SW ML a

Spr ng

A

BcfMin.)

~

— — — Bedding

Haunch — See Table 27 SB Laser Side — See Table 2758

See Table 2758] ““—Middle Bedding Outer Beddielg II loosely placed materials a~ ,fls.L4...4 uncanipacted bedd.ng compaction each side, same tIGEND: requirements Bc = Outside Diameter as haunch roundalion H = Backlill caner abore -

top at pipe

ARCH PIPE FIGURE 27.5C

Trench Beddings, Miscellaneous Shapes

(peat, muck, etc.) is encountered at or below invert elevation during excavation, the necessary subsurface exploration and analysis shall be made and corrective treatment shall be as directed by the Engineer. 27.5.2.2

Precast Reinforced Concrete Circular Arch and Elliptical Pipe

A bedding shall be provided for the type of installation specified conforming to Figures 27.5A, 27.5B, 27.5C, and 27.5D which define soil areas and critical dimensions, and Tables 27.SA and 27.5B, which list generic soil types and minimum compaction requirements, and minimum bedding thicknesses for the four Standard Installation Types.

27.5.2.3

Precast Reinforced Concrete Box Sections

A bedding shall be provided for the type of installation specified conforming to Figure 27.5E unless in the opinion of the Engineer, the natural soil provides a suitable bedding. 27.5.3

Placing Culvert Sections

Unless otherwise authorized by the Engineer, the laying of culvert sections on the prepared foundation shall be started at the outlet and with the spigot or tongue end pointing downstream and shall proceed toward the inlet

27.5.3

HIGHWAY BRIDGES

616

Overfill OcrIll

—

Bc/6 Mm.)

Bc

SW. ML or CL.

Bc Mm.

Haunch — See Table 27.5A

Haunch — See Table 27 SA Laser Side — See Table 275A

Spring

Bedding

—

SW. ML. or CL

Spring L~ne~~\

See Table 27 5A.—/~ ““Middle Bedding Outer Bedding loosely placed materials and uncompacted bedding campa~tian each Bc/3 sidp, same requrements Foundation LIGENO: an haunch Bc = Outside Diameter H = Backfill cover above top at pipe

Lower Side — See Table 27.5A

—

Bedding

See Table 27.5A—

-

Outer Bedd~n~ can1paO,~n each r*quwente~li as hounch

—

—

LfGEND: Bc — Outside Diameter H — BarkIll caner above top at pipe

SW. ML. or CL Bc/

Bedding

Fow,dOton

VE~1CAL EWPTICAL PIPE

HORIZONTAL ELUPliCAL PIPE

Overfill

““—Ididdle Bedding loosely placed uncompacted bedding

~

Mm.

Bc H

See Table 27.SA

materials and compaction each side, same requirements as haunch

M.ddle Bedding Bc/3

/

Bc Mm.

,.—

uncompacted bedding LEGEND: Bc — Outside Dameter H — Backfill corer above top at pipe

Foundation

ARCH PIPE FIGURE 27.5D

Embankment Beddings, Miscellaneous Shapes

end with the abutting sections properly matched, true to the established lines and grades.. Where pipe with bells is installed, bell holes shall be excavated in the bedding to such dimensions that the entire length of the barrrel of the pipe will be supported by the bedding when properly installed. Proper facilities shall be provided for hoisting and lowering the sections of culvert into the trench without disturbing the prepared foundation and the sides of the trench. The ends of the section shall be carefully cleaned before the section is jointed. The section shall be fitted and matched so that when laid in the bed it shall form a smooth. uniform conduit. When elliptical pipe with circular reinforcing or circular pipe with elliptical reinforcing is used, the pipe shall be laid in the trench in such position that the markings “Top” or “Bottom.” shall not be more than 50 from the vertical plane through the longitudinal axis of the pipe.

Multiple installations of reinforced concrete culverts shall be laid with the center lines of individual barrels parallel at the spacing shown on the plans. Pipe and box sections used in parallel installations require positive lateral bearing between the sides of adjacent pipe or box sections. Compacted earth fill, granular backfill, or grouting between the units are considered means of providing positive bearing. 27.5.4

Haunch, Lower Side and Backfill or Overfill

27,5.4.1

27.5.4.1.1

Precast Reinforced Concrete Circular Arch and Elliptical Pipe Haunch Material

Haunch material shall be installed to the limits shown on Figure 27.5A, 27.5B, 27.5C, and 27.51).

:

DIVISION LI—CONSTRUCTION

27.5.4.1.1

617

TABLE 27.5A Standard Embankment Installation Soils and Minimum Compaction Requirements Haunch and Outer Bedding

Installation Type

Bedding Thickness

Type I

B~/24” minimum, not less than 3”. Ifrock foundation, use B~/t 2” minimum, not less than 6”

95% SW

Type 2

Bj24” minimum, not less than 3”. If rock foundation, use B~/l2” minimum, not less than 6”

90% SW or 95% ML

B~/24” minimum, not less than 3”. Ifrock foundation, use B~/l2” minimum, not less than 6”

85% SW, 90% ML, or 95% CL

85% SW, 90% ML or 95% CL

No bedding required, except if rock foundation, use Bjt2” minimum, not less than 6”

No compaction required, except if CL, use 85% CL

No compaction required, except if CL, use 85% CL

(See Note 3.)

Type 3 (See Note 3.)

Type 4

Lower Side 90% SW, 95% ML or 100% CL

85% SW,

90% ML

or 95% CL

NOTES t. Compaction and soil symbols—ic. “95% SW’ refers to SW soil material with a minimum standard proctor compaction of 95%. See Tabte 27.5C for equivaleni modified procior values. 2. Soit in the outer bedding, haunch, and lower side zones, except within Bj3 from the pipe springtine, shalt be compacted to at least the same compaction as the majority ofsoit in the overfill zone. 3. Only Type 2 and 3 instaltalions are available for horizontal ettipticat, vertical ellipticat and arch pipe. 4. SUBTRENCHES 4. t A subirench is defined as a trench with its mop below finished grade by more than 0.1 H or. for roadways. its top is at an elevation lower than 1’ below the bottom of the pavement base material. 4.2 The minimutn width of a sublrench shall be 1.33 B,., or wider if required for adequate space in atmain mIsc specified compaction in the haunch and bedding zones. 4.3 For subtrenches with watts of natural soil, any portion of the tower side zone in the subsrench wall should be at least as firm as an equivatent soil placed to the compaction requirements specitied for the lower side zone and as firm as the majority of soil in the overfill zone, or shalt be rensosed and replaced with soil compacted mo the specilied level.

:

27.5.4.1.1

HIGHWAY BRIDGES

618

TABLE 27.5B Standard Trench Installation Soils and Minimum Compaction Requirements Haunch and Outer Bedding

Installation Type

Bedding Thickness

Type I

Bj24” minimum, not less than 3’’. If rock foundation, use B~/l2” minimum, not less than 6”

95% SW

90% SW, 95% ML 100% CL, or natural soils of equal firmness

Type 2

B~/24” minimum, not less than 3”. tf rock foundation, use BJ12” minimum, not less than 6’’

90% SW or 95% ML

85% SW, 90% ML

B,I24” minimum, not less than 3’’. If rock foundation, use B~/l 2” minimum, not less than 6”

85% SW, 90% ML, or 95% CL

85% SW, 90% ML 95% CL, or natural soils of equal firmness

No bedding required, except if rock foundation, use B~/l2” minimum, not less than 6”

No compaction required, except if CL, use 85% CL

85% SW, 90% ML 95% CL, or natural soils of equal firmness

(see Note 3)

Type 3 (see Note 3)

Type 4

Lower Side

95% CL, or natural soils of equal firmness

NOTES I. Compaction and soil symbols—i.e. ..95~3f SW~ refers to SW soil material with a minimum standard proctor compaction of 95%. See Table 27.5C for equivalent modified proctor values. 2. The trench top elevation shall be no lower than .0.1 H below finished grade or, for roadways, its top shall be no lower than an elevation of I’ below the bottom of the pavement base material. 3. Only Type 2 and 3 installations are available for horizontal elliptical, vertical elliptical and arch pipe. 4. Soil in bedding and haunch zones shall be compacted to at least the same compaction as specified for the majority of soil in the backfill zone. 5. The trench width shalt be wider than shown if required for adequate space to attain the specified compaction in the hauneh and bedding zones. 6. For trench walls that are within tO degrees of vertical, the compaction or firmness of the soil in the trench walls and lower side zone need not be considered. 7. For trench walls with greater than 10-degree slopes that consist of embankment, the tower side shall be compacted to at least the same compaction as specified for the soil in the backfill zone.

27.5.4.1.2

DIVISION 11—CONSTRUCTION TABLE 27.5C

619

Equivalent USCS and AASHTO Soil Classifications for SIDD Soil Designations Representative Soil Types

Percent Compaction Standard Proctor

Modified Proctor

AI,A3

100 95 90 85 80 61

95 90 85 80 75 59

GM, SM, ML Also GC, SC with less than 20% passing No. 200 sieve

A2, A4

100 95 90 85 80 49

95 90 85 80 75 46

GL, MH GC, SC

AS, A6

100 95 90 85 80 45

90 85 80 75 70 40

CH

A7

100 95 90 45

90 85 80 40

SIDD Soil

USCS

AASHTO

Gravelly Sand (SW)

SW, SP GW, GP

Sandy Silt (ML)

Silty Clay (CL)

27.5.4.1.2

Lower Side Material

Lower side material shall be installed to the limits shown on Figures 27.5A, 27.5B, 27.5C, and 27.5D. 27.5.4.1.3

Overfill

Overfill material shall be installed to the limits shown on Figures 27.5A. 27.5B. 27.5C, and 27.5D.

27.5.4.2

27.5.4.2.1

Precast Reinforced Concrete Box Sections

Backfill

Backfill material shall be installed to the limits shown on Figure 27.5E for the embankment or trench condition. Trenches shall have vertical walls and no over-excavating or sloping sidewalls shall be permitted.

27.5.4.3

Placing of Haunch, Lower Side and Backfill or Overfill

Generally, compaction of fill material to the required density is dependent on the thickness of the layer of fill being compacted, soil type, soil moisture content, type of compaction equipment, and amount of compactive force and the length of time the force is applied. Fill material shall be placed in layers with a maximum thickness of 8 inches and compacted to obtain the required density. The fill material shall be placed and compacted with care under the haunches of the culvert and shall be brought tip evenly and simultaneously on both sides of the culvert. For the lower haunch areas of Type 1, 2, and 3 Standard Installations, soils requiring 90 percent or greater Standard Proctor densities shall be placed in layers with a maximtimn thickness of 4 inches and compacted to obtain the required density. The width of trench shall be kept to the minimum required for installation of the culvert. Ponding or jetting will be only by the permission of the Engineer.

27.5.4.4

HIGHWAY BRIDGES

620 Backfill

Ex,gting ground or fill

BOX SECTIONS EMBANKMENT BEDDING

Compacted Granular Material

Bedding

BOX SECTIONS TRENCH BEDDING FIGURE 27.5E

27.5.4.4

Cover Over Culvert During Construction

Culverts shall be protected by a minimum of 3 feet of cover to prevent damage before permitting heavy construction equipment to pass over them during construction. 27.6

MEASUREMENT

Culverts shall be measured in linear feet installed in place, completed, and accepted. The number of feet shall be the average of the top and bottom center line lengths for pipe and box seettons.

27.7

PAYMENT

The length determined as herein given shall be paid for at the contract unit prices per linear foot bid for culverts of the several sizes and shapes, as the case may be, which prices and payments shall constitute full compensation for furnishing, handling, and installing the culvert and for all materials, labor, equipment, tools, and incidentals necessary to complete this item. Such price and payment shall also include excavation, bedding material, backfill, reinforced concrete headwalls and endwalls, and any required foundations.

Section 28 WEARING SURFACES 28.1

If not otherwise shown on the plans, the minimum thickness of latex modified concrete wearing surfaces shall be 11/4 inches.

DESCRIPTION

This work shall consist of placing a wearing surface of durable and impervious material on the roadway surface of bridge decks. It also includes the preparation of the surfaces of either existing or new decks to receive such an overlay of surfacing material. The type and thickness of the wearing surface shall be as designated on the plans. The materials and installation requirements for wearing surfaces of types other than latex modified concrete shall be as specified in the special provisions~. Latex modified concrete wearing surfaces shall be furnished and installed in accordance with these specifications. 28.2

28.2.1

28.2.2

Materials

28.2.2.1

Portland Cement

Portland cement shall conform to the requirement of Article 8.3.1 of Section 8, “Concrete Structures,” except that only Types I or II shall be used. 28.2.2.2

Aggregate

Aggregate shall ct)nfortTi to the requirements of AASHTO M 6 for fine aggregate and to AASHTO M 80 for coarse aggregate. Coarse aggregate shall be graded ‘/2 inch to No. 4 per AASHTO M 43.

LATEX MODIFIED CONCRETE TYPE WEARING SURFACE General

28.2,2.3

All equipment used to prepare the surface and to proportion, mix, place and finish the latex concrete shall be subject to approval by the Engineer prior to use. This approval will be contingent on satisfactory perfortnance and will be rescinded in the event such performance is not being achieved. Eqtiipment shall be on hand sufficiently ahead of the start of construction operations to be examined and approved. Any equipment leaking oil or any other containment onto the deck shall be immediately removed from the job site until repaired. A technician who is well experienced in the proportioning. mixing. placing and finishing of latex modified concrete shall be employed by the Contractor and shall be present and in technical control of the work whenever these operations are underway. The qualifications of this technician which includes a list of projects on which the technician was employed and the technician’s level of responsibility on each shall be submitted to and approved by the Engineer prior to the start of these operations. Approval by the Engineer of equipment or technicians shall not relieve the Contractor of any responsibility under the contract for the successful completion of the work.

Water

Water for mixing concrete shall conforni to the requirements of Article 8.3.2. 28.2.2.4

Latex Emulsion

Formulated latex emulsion admixture shall be a nonhazardous, film forming. polymeric emulsion in water to which all stabilizers have been added at the point of manufacture and shall be homogeneous and uniform in coFnpoSition. Physical Properties—The latex modifier shall conform to the following requirements: Polymer Type Stabilizers Styrene Butadiene (a) Latex Nonionic Surfactants (b) Portland Cement Composition Polydimethyl Siloxane Percent Solids 46.0—49.() 0C) 8.4 Weight per Gallon (lbs at 25 Color White 621

622

HIGHWAY BRIDGES

A Certificate of Compliance signed by the manufacture of the latex emulsion certifying that the material conforms to the above specifications shall be furnished for each shipment used in the work. Latex admixture to be stored shall be kept in suitable enclosures which will protect it from freezing and from 0F. prolonged exposure to temperatures in excess of 85 Containers of latex admixture may be stored at the bridge site for a period not to exceed 10 days. Such stored containers shall be covered completely with suitable insulating blanket material to avoid excessive temperatures. 28.2.2.5

Latex Modified Concrete

The latex modified concrete for use on this project shall be a workable mixture and meet the following requirements. Material or Property Cement (Parts by weight) (Note 3) Fine Aggregate (Parts by weight) (Note 3) Coarse Aggregate (Parts by weight) (Note 3) Latex Emulsion Admixture(GaIs/Bag Cement) Air Content of Plastic Mix, % (AASHTO T 152) Slump, Inches (Notes 1 and 2)

Concrete

28.2.2.4

walls, etc., up to a height of 1 inch above the top elevation of the overlay shall be blast cleaned to a bright, clean appearance which is free from laitance. curing compound, dust, dirt, oil. grease. bituminous material, paint, and all foreign matter. The blast cleaning of an area of the deck shall normally be performed within the 24-hour period preceding placement of the overlay on the area. The blast cleaning may be performed by either wet sandblasting. high pressure water blasting, blasting grits, shrouded dry sandblasting with dust collectors, or other method approved by the Engineer. Water blasting equipment shall operate with a minimum pressure of 3,500 psi. The method used shall be performed so as to conform to applicable air and water pollution regulations and to applicable safety and health regulations. All debris, ineltiding dirty water, resulting from the blast cleaning operations shall be immediately and thoroughly cleaned from the blast-cleaned surfaces and from other areas where debris

2.5 2.0

may have accumulated. The blast cleaned areas shall be protected, as necessary, against contamination prior to 1placement of the overlay. Contaminated areas and areas exposed more than 36 hours after cleaning shall be blast cleaned again as directed by the Engineer at the Contrac-

3-6 3-6

tors expense. Just prior to placement of the overlay, all dust and other debris shall be removed by flushing with water or blowing with compressed air. The prepared surface shall then be soaked with clean water for not less than 1 hour prior

________

the placement of the latex overlay. Before the overlay is applied, all free water shall be blown out anLI off, and this procedure shall continue until the surface appears LIrY or barely damp. The air supply system for blast cleaning and blow immg shall be equipped with an oil trap in the air line, amid provisions shall be made to prevent oil or grease contamimla— tion of the surface by any equipment prior to placement of the overlay. tt)

NOTES: Following sampling of the discharged. normally mixed material, the commencement of the slump test shall be delayed from 4 to 5 mintites. 2. Water may be added to obtain slLimp within the prescribed limits. 3. The dry weight ratios are approximate and should produce good workability, but due to oradation changes may be adjusted within litnits by the Engineer. The parts by weight of sand may be increased by as much as 0.2 if the coarse aggregate is reduced by an equivalent volume. 28.2.3

Surface Preparation

28.2.3.1

New l)ecks

The surfaces of new decks Lt~Ot1 which a wearirmgsurface overlay is to be placed shall be finished to a rotigh texture by coarse brooming or other approved tnethods. After etiring tsf the deck concrete is complete and belore placing the overlay, the entire area of the deck surface and the vertical faces of ctmrbs. concrete parapets, barrier

28.2.3.2

Existing Decks

The surface of existirmg decks that have become contaminated by traffic usage or by deicing salts shall be scarified to the depth shown on the plaits or specified. If no depth is shown or specified, a mninimtmm of - inch of material shall be removed by scarification. Prior to beginning scarification and until operations are ct)mpleted. all deck drains, expansion joints and other openings where damage could result. as determined by the Engineer, shall be temporarily covered or plugged to prevent entry of debris. Scarifying shall be done with power-operated mnecharmmeal scarifiers, or other approved devices, capable of urmifonmnly removing the existing surface to the depths re-

DIVISION 11—CONSTRUCTION

281.3.2

quired without damaging the underlying concrete. Machine scarifiers shall not be operated so as to damage hardware such as drain grates and expansion joint armor. In areas where machine scarifying cannot reach and in areas t)f spalling and where steel reinforcement is exposed, scarifying and the removal of deteriorated or unsound concrete shall be acconiplished with hamid tools. Pnuematic hammers heavier than nominal 45 pounds shall not be used. No scarifying or chipping will be allowed within 6 feet of a new overlay until 48 hotirs after its placement. In areas where deteriorated or unsound concrete is encourmtered. as determined by the Engimieem. the concrete shall be removed to a depth of 4-inch below the top mat of reinforcimig steel. A minimum oh 4—inch clearance shall be required around the reinforcing steel except where lower bar mats make this impractical. Care shall be exercised to prevent damaging the exposed reinforcing steel. All reinforcing steel shall be blast-cleaned. The repair areas am-c to be filled during the overlay operation. After scarificatiomi and removal of tmnsound concrete has been completed. the deck surface shall be blast cleaned and prepared as specified for rmew (leeks. 28.2.4

Proportioning and Mixing

The Conlractor shall submit to the Engimicer for approval. 14 calendar (lays prior to date of placement. the propose(l mix design in writing and samples of all mix materials in sufficient quantity to produce a minimum of 3 cubic feet of concrete for laboratory mix (Iesign testing. Proptirtioning and mixing equipment shall be of a self— contained. mobile. comitinLmous—miximic. volumetric pro— portimning type mixer. Continuous—type mnixers shall be eqttippe(l so that the proportions of the cement, natural sand, and coarse aggregate can be fixed by calibration of the mnixer and cannot be changed without (lestroving a seal or other indicatinc device affixed to the mixer. In additiomi to being equipped with a flow meter for calibratimig the water sup— ply portion of the miii xer. the mu ixer shall also be equipped with a cummulatix c—type water tneter which can be reai.f to the nearest t). 1 gallon. The water miieters shall be readily accessible, accurate to with imi 1 percent. and easy to read. l3oth water meters shall be subject to checking by the En— eiiieer each time the miiixer is calibrated. A 1i1iroved methods for adding the admi xttire shall be provided. The ad— mixtures shall be added so as to be kept separated as far as i pract icahile. The conti iiuous type milixer shall be calibrated to the satisfactiomi of the F.ncimi ccr ~ or to starting the xx ork. Yield checks norniallv will be nmade for each 51) cubic yards of mu ix. Recalibratiomi will be riecessars when imiLhicated bx ttie yield checks, amid at ~mvut her times

623

the Engineer deems necessary to ensure proper proportioning of the ingredients. Continuous type mixers which entrap unacceptable volumes of air in the mixture shall not be used. The mixer shall be kept cleati and free of partially dried orhardened materials at all titnes. It shall consistently prssduce a uniform. thoroughly blended mixture withiii the specified air content amid slump limits. Malfunctionitig mixers shall be imniediately repaired or replaced with acceptable units. Aggregate stockpiles being used shommld be of unifortii moisture content. Mixing capability shall be sLich that fimiishinc operations can pr(iceed at a steady pace with final finishimic completed before the forniation of the plastic surface film. 28.2.5

Installation

28.2.5.1

Weather Restrictions

The placernemit of latex niodified comicrete shall not be started when is expected to rain fall 0F orthe risetemperature above 800F. is, or or when high xvitids, below 45 or low humidity conditions are expected prior to tinal set the comicrete. If any of these comiditiomis (icctlr dLmrimic placenient. the placenient shall be terinirmated and a straight comistruictiomi joitit fornied. Placemiiemit at miiglit iiiay be miecessary xvliemi daytimiie comiditions are not favorable. If placement is performed am miiglit. adeqtmate lighting shall be pr(ivided by the Contractor. tif

28.2.5.2

Equipment

Placi mig amid timlishiimig eqLmifuiiicmit shall imiel tide humid t(i(il s for placenietit amid brLmshimig—imi freslil v mixed latex modified comicrete amid for distributimig it to approx match the correct level for striking—off xuitli the screed. Vlamid—o 1ierate(l vibrators. screeds amid floats shall be Lised for comi— ssihidati tic and finishing smiiall areas. Ami approved titiishi in c iiiaehi tie comuplvimig xx ith the folloxx imic reqtsiremiierits shall be used for timii sliimic all large areas of work:

The tiiiishiimi c miiaehine shah be sel f—prohiel led amid ca— 1uahle of forward amid reverse iioxemiiemit under pLisilixe control. The lertethi (if the screed shall be suiffic emit t(i extemid at least 6 inches bevomid the eLlce (if both emi(ls (if the seetiomi beimig placed. The finishing miiachimie shall also be capable of consol dati tic the cotierete by v ibratioti and of rai simig all screeds to clear the comicrete for travelituc iii reverse. The machi tie shall be either a rotatimig ref IL’r Ivhuc or arm (iscillatitic screed type.

28.2.5.2

HIGHWAY BRIDGES

624

Rotating roller-type niachines shall have one or more rollers, augers, and 1,500 to 2,500 vpm vibratory pans. Oscillating screed-type machines shall have vibrators on the screeds whose frequency of vibration can be varied between 3,000 and 15,000 vpm. The bottom face of the screeds shall be not less than 4 inches wide and shall be metal. Rails will be required for the finishing machine to travel on. Rails shall be sufficiently rigid to support the weight of the machine without appreciable deflection and shall be placed outside of the overlay area. Rail anchorages shall provide horizontal and vertical stability and shall not be ballistically shot into concrete that will not be overlaid. A suitable portable lightweight or wheeled work bridge shall be furnished for use behind the finishing operation. 28.2.5.3 28.2.5.3.1

Placing and Finishing Construction Joints

Planned construction joints shall be formed by bulkheads set to grade. Before placing concrete against previously placed overlay material, the construction joint shall be sawed to a straight vertical edge. Sawing ofjoints may be omitted if the bulkhead produces a straight, smooth, vertical surface. The face of the joint shall be sand or water blasted to remove loose material. Longitudinal construction joints will be permitted only at the center line of roadway or at lane lines unless otherwise shown on the plans or permitted by the Engineer. In case of delay in the placement operatmon exceeding I hour in duration. an approved construction joint shall be formed by removing all niaterial not up to finish grade and sawing the edge in a straight line. During minor delays of 1 hour or less, the end of the placement may be protected from drying with several layers of clean, wet burlap. 28. 2. 5.3.2

Placing

The finishing niachine shall be test run over the entire area to be tiverlayed each day before placement is started to ensure that the required overlay thickness will be achieved. Imniediately ahead of placimig the overlay niixture, a thin coating (if the polymer modified concrete mixture to be used for the overlay shall be thoroughly brushed and scrubbed onto the surface as a grout-bond coat for the overlay. Coarser particles of the niixture which cannot be scrubbed into contact with the surface shall be renioved amid disposed of in a tiianner approved by the Engineer. Care shall be taken to insure that all vertical as well as horizontal sLirfaces receive a thorough. even c(iating and that

the rate of progress is limited so that the material brushed on does not become dry before it is covered with the full depth of latex modified concrete. The latex modified concrete shall be placed on the prepared and grout-coated surface immediately after being mixed. The mixture shall be placed and struck off approximately 1/4 inch above final grade then consolidated by vibration and finished to final grade with the appr(ived finishing machine. Spud x’ibrators will be required in deep pockets, along edges, and adjacent to joint bulkheads. Supplemental vibration shall be provided along the meet lines where adjacent pours come together and along curb lines. Hand finishing with a float may be required along the edge of the pour or on small areas of repair. Screed rails and construction bulkheads shall be separated from the newly placed material by passing a pointing trowel along their inside face. Expansion dams shall not be separated from the overlay. Care shall be exercised to ensure that this trowel cut is made for the entire depth and length of rails after the mixture has stiffened sufficiently. 28.2.5.3.3

Finishing

The finishing equipment shall be operated so as to produce a uniform, smooth, and even-textured surface. The final surface shall not vary more than /~ inch from a 10-foot straightedge placed longitudinally thereon. Before the plastic film forms, the surface shall be textured by tining in accordance with the requirements of Article 8.10.2.3. 28.2.6

Curing

The surface shall be promptly covered with a single layer of clean, wet burlap as soon as the surface will support it without deformation. Within 1 hour of covering with wet burlap. the burlap shall be rewet if necessary and a layer of 4-mil polyethylene film, or wet burlap-polyethylene sheets, shall be placed on the wet burlap, and the surface cured for 24 hours. The curing niaterial shall then be removed for an additional 72 hours of air cure. If the temperature falls below 450 during curing, the duration of the wet cure shall be extended as directed by the Engineer. The overlay shall be protected frotii freezing during the cure period. Traffic will not be permitted on the overlay while it is curing. 28.2.7

Acceptance Testing

After curiiig is conipleted, the (iverlay will be x’isually imispected f(ir crackimig or other damage. and imispected for Lielamimiatitins and bond failuires by the use of a chain drag ~irother suitable (levice.

DIVISION 11—CONSTRUCTION

28.2.7

Surface cracks not exceeding ~/8 inch in depth shall be sealed with an epoxy penetrating sealer followed by an application of approved sand. Any cracks exceeding Vs inch in depth shall be repaired by methods approved by the Engineer, or the affected portions of the wearing surface shall be removed and replaced. Any delaminated or unbonded portions of the wearing surface or portions damaged by rain or freezing shall be removed and replaced. After completion of the wet cure, the surface shall be tested for flatness and corrected, if necessary, as provided in Article 8.10.2.4. All corrective work will be at the Contractor’s expense. 28.2.8

Measurement and Payment

Wearing surfaces and areas requiring scarification will be measured by the square foot based on dimensions of the completed work.

625

Wearing surfaces will be paid for at the contract price per square foot. Except as otherwise provided, the payment per square foot for wearing surfaces shall be considered to be full compensation for the cost of furnishing all labor, materials, equipment, incidentals, and for doing all work involved in preparing the surface and constructing the wearing surface as shown on the plans and specified. When a separate item is included in the bid schedule for scarifying bridge decks, scarifying will be paid for by the contract price per square foot. Such payment shall be considered to be full compensation for all costs involved with the scarifying work including removal and disposal of debris. The removal of unsound concrete which is encountered below the depth specified for scarifying will be paid for as extra work.

Section 29 EMBEDMENT ANCHORS

29.1

29.4

DESCRIPTION

This specification covers installation and field testing cast-in-place, grouted. adhesive-bonded, expansion and undercut steel anchors.

Provide adequate edge distance, embedment depth and spacimig to develop the required strength of the enibedment anchors. Use the correct drill hole diameter as per manufacturer’s instructions. Use rotary impact drilling equipment unless diamond core drilling has been specified and tested. If reinforcing bar is encountered during the drilling operation, move to a different location, or drill through the reinforcing steel using a diamond core bit as directed by the Engineer. Patch abandoned holes with ami approved bonding material. Clean holes thoroughly as recomniended by the nianufacttinrer. Remove all loose dust and concrete particles froni hole. Prepare bonding material and install anchors according to instructions provided by the manufacturer tir approved by the Emigineer. Embedded anchors which are iniproperly imistalled uir which do not have the reqtired strength shall be remiioved and replaced to the satisfactiomi of the Emucineer at the Contractor’s expense.

(if

29.2

PREQUALIFICATION

PreqLlahify all concrete anchors, includimig cast-inplace. all bonded ammehior systems (including grtiut, chemnteal compounds, and adhesives), and mndercut by universal test stamidards designed to allow approved anchor systenis to be employed for amiy construction attachnient use. Comiduct test for a(hhiesive-b(inded aiid tither bonding c(inip(iunds iii accordance with ASTM F 15 12 (Standard Test Methods for Testimic Bond Performance (if AdhesiveBonded Anchors). Test expamisiomi types to ASTM E 488 standards (Standard Test Methods for Stremigtli (if Anchors iii Concrete and Masonry Fleniemits). Comply with ACI 349-85 (Code Requiremnemits for Nuclear Safety Related Concrete Structures—Appendix B. Steel Embedmiiermts). Provide certified test reliorts prepared byan indepemidetit laboratory LI(icumiiemi titig that the systemii (except mug— chanical expansiomi amichiors 1 is capable (if achievimic the mimii tiititii tetisi he stremigth tif the embedmimerit steel. 29.3

CONSTRUCTION METHODS

29.5

INSPECTION AND TESTING

Where specified. condtmct sacrificial tests of the anchor system on the .Iob site to umhtimimate loads to h(icumiiemit the capability of the system to achieve puhhomt loads equahimug the full miiimiimumm temisile value of the amichor eniploved. Test the amichor (iii ftthhx cured etimierete samiiples. h/miless specified titlierwise. test rio fewer thati three 3) anchors by ASTM E 488 methods. The Comitractor may use an~ p~—

MATERIALS

qualified amichior systemiis miueetmmig the above reqLiireniemits. Provide, without delax in progress. for an alternate sx s— temii that will reach the uhesi gmiated pull—ri nt red~Li i remiiemit it the ob site proofloadirig proves incapable of achuievi tie miiimiirnuni temisile xaltmes or the desi giier~s required load if too little comucrete exists in xvhichi to develop tLlh I uhiict he loads~. After imustalhimuc the curi tic of bomuding material. torqume each anchor svstemii t(i values specified. If t(iruhue values are riot sped tied. use vahLmes rccouiitiiemided by the mann— facturer dir provided by the Etugmneer.

Provide mull test reports cert i k imig ~~hiysicah properties. chemiiistrv. and stremigths. The chiemii cal coumpoumids acceptable for adhesi ye ami— chiors may iii cltmde epoxies. 1iohyesters. or vimivhesters Ad— liesi ye comiipotmmids su hiichm are muioisture—miisemismtm ye. high— timoLlulus. hi i ghi—stremiethi. amid how—shrinkage should be ii~t’d. The use of aduf it ix es to g rout. amiul bomid i ng ni ateri aIs which will be corrosive t steel or ~inc/cadmiiiittii coatmmigs is prohibited. 627

HIGHWAY BRIDGES

628 29.6

MEASUREMENT

Count and summarize each embedment anchor type satisfactorily installed for the Contract, according to anchor system, orientation (vertical, diagonal, and horizontal). and size (diameter).

29.7

296

PAYMENT

Payment for the quantity of embedment anchors determined under measurement for each embedment anchor type, shall include full compensation for furnishing all labor, materials, tools, equipment, testing, and incidentals necessary to place each anchor type.

APPENDIX A LOADING—H 15-44 (Ml3.5) TABLE OF MAXIMUM MOMENTS, SHEARS, AND REACTIONS— SIMPLE SPANS, ONE LANE Spans in feet; moments in thousands of foot-pounds; shears and reactions in thousands of pounds. These values are subject to specification reduction for loading of multiple lanes. Impact not included. Moment

End shear and end reaction (a)

Span

2 3 4 5 6 7 8

6.0(b) 12.0(b) 18.0(b) 24.0(b) 30.0(b) 36.0(b) 42.0(b) 48.0(b)

24.0(b) 24.0(b) 24.0(b) 24.0(b) 24.0(b) 24.0(b) 24.0(b) 24.0(b)

42 44 46 48 50 52 54 56

Span

Moment

End shear and end reaction (a)

9

54.0(b)

24.0(b)

58

10

60.0(b)

24.0(b)

60

274.4(b) 289.3(b) 304.3(b) 319.2(b) 334.2(b) 349.1(b) 364.t(b) 379.1(b) 397.6 418.5

II 12 13 14 15

66.0(b) 72.0(b) 78.0(b) 84.0(b) 90.0(b)

24.0(b) 24.0(b) 24.0(b) 24.0(b) 24.0(b)

62 64 66 68 70

439.9 461.8 484.1 506.9 530.3

34.4 34.9 35.3 35.8 36.3

16 17 t8 19 20

96.0(b) 102.0(b) 108.0(b) 114.0(b) 120.0(b)

24.8(b) 25.1(b) 25.3(b) 25.6(b) 25.8(b)

75 80 85 90 95

590.6 654.0 720.4 789.8 862.1

37.5 38.7 39.9 41.1 42.3

21 22 23 24 25

126.0(b) 132.0(b) 138.0(b) 150.0(b)

26.0(b) 26.2(b) 26.3(b) 26.5(b) 26.6(b)

100 110 120 130 140

937.5 1,097.3 1,269.0 1,452.8 1,648.5

43.5 45.9 48.3 50.7 53.1

26 27 28 29 30

156.0(b) 162.7(b) 170.1(b) 177.5(b) 185.0(b)

26.8(b) 26.9(b) 27.0(b) 27.1(b) 27.2(b)

150 160 170 180 190

1,856.3 2,076.0 2,307.8 2,551.5 2,807.3

55.5 57.9 60.3 62.7 65.1

31 32 33 34 35 36 37 38 39

192.4(b) 199.8(b) 207.3(b) 214.7(b) 222.2(b) 229.6(b) 237.1(b) 244.5(b) 252.0(b)

200 220 240 260 280 300

3,075.0 3,646.5 4,266.0 4,933.5 5,649.0 6,412.5

67.5 72.3 77.1 81.9 86.7 91.5

40

259.5(b)

27.3(b) 27.4(b) 27.5 27.7 27.9 28.1 28.4 28.6 28.9 29.1

144.0(b)

29.6 30.1 30.5 31.0 31.5 32.0 32.5 32.9 33.4 33.9

(a) Concentrated load is consideredplaced at the support. Loads used are those stipulated for shear. (b) Maximum value determined by Standard Truck Loading. Otherwise the Standard Lane Loading governs. 629

App. A

HIGHWAY BRIDGES

630

LOADING—HS 15-44 (M13.5) TABLE OF MAXIMUM MOMENTS, SHEARS, AND REACTIONS— SIMPLE SPANS, ONE LANE Spans in feet; moments in thousands of foot-pounds; shears and reactions in thousands ofpounds. These values are subject to specification reduction for loading of multiple lanes. Impact not included. Span

Moment

End shear and end reaction (a)

Span

Moment

End shear and end reaction (a)

1 2 3 4 5

6.0(b) 12.0(b) 18.0(b) 24.0(b) 30.0(b)

24.0(b) 24.0(b) 24.0(b) 24.0(b) 24.0(b)

42 44 46 48 50

364.0(b) 390.7(b) 417.4(b) 4.44.1(b) 470.9(b)

42.0(b) 42.5(b) 43.0(b) 43.5(b) 43.9(b)

6 7 8 9 10

36.0(b) 42.0(b) 48.0(b) 54.0(b) 60.0(b)

24.0(b) 24.0(b) 24.0(b) 24.0(b) 24.0(b)

52 54 56 58 60

497.7(b) 524.5(b) 551.3(b) 578.1(b) 604.9(b)

44.3(b) 44.7(b) 45.0(b) 45.3(b) 45.6(b)

II 12 13 14 15

66.0(b) 72.0(b) 78.0(b) 84.0(b) 90.0(b)

24.0(b) 24.0(b) 24.0(b) 24.0(b) 25.6(b)

62 64 66 68 70

631.8(b) 658.6(b) 685.5(b) 712.3(b) 739.2(b)

45.9(b) 46.1(b) 46.4(b) 46.6(b) 46.8(b)

16 17 18 19 20

96.0(b) 102.0(b) 108.0(b) 114.0(b) 120.0(b)

27.0(b) 28.2(b) 29.3(b) 30.3(b) 31.2(b)

75 80 85 90 95

806.3(b) 873.7(b) 941.0(b) 1,008.3(b) 1,074.9(b)

47.3(b) 47.7(b) 48.1(b) 48.4(b) 48.7(b)

21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

126.0(b) t32.0(b) 138.0(b) 144.5(b) 155.5(b) 166.6(b) 177.8(b) 189.0(b) 200.3(b) 211.6(b) 223.0(b) 234.4(b) 245.8(b) 257.7(b) 270.9(b) 284.2(b) 297.5(b) 310.7(b) 324.0(b) 337.4(b)

32.0(b) 32.7(b) 33.4(b) 34.0(b) 34.6(b) 35.1(b) 35.6(b) 36.0(b) 36.6(b) 37.2(b) 37.7(b) 38.3(b) 38.7(b) 39.2(b) 39.6(b) 40.0(b) 40.4(b) 40.7(b) 41.1(b) 41.4(b)

100 110 120 130 140 150 160 170 180 190 200 220 240 260 280 300

1,143.0(b) 1,277.7(b) 1,412.5(b) 1,547.3(b) 1,682.1(b) 1,856.3 2,076.0 2,307.8 2,551.5 2,807.3 3,075.0 3,646.5 4,266.0 4,933.5 5,649.0 6,412.5

49.0(b) 49.4(b) 49.8(b) 50.7 53.1 55.5 57.9 60.3 62.7 65.1 67.5 72.3 77.1 81.9 86.7 91.5

(a) Concentrated load is considered placed at the support. Loads used are those stipulated for shear. (b) Maximum value determined by Standard Truck Loading. Otherwise the Standard Lane Loading governs.

App. A

HIGHWAY BRIDGES

631

LOADING—H 20-44 (M 18) TABLE OF MAXIMUM MOMENTS, SHEARS, AND REACTIONS— SIMPLE SPANS, ONE LANE Spans in feet; moments in thousands of foot-pounds; shears and reactions in thousands of pounds. These values are subject to specification reduction for loading of multiple lanes. Impact not included. Span

Moment

8.0(b)

End shear and end reaction (a)

Span

32.0(b) 32.0(b) 32.0(b) 32.0(b) 32.0(b)

42 44 46 48 50

405.7(b) 425.6(b) 445 .6(b)

39.4 40.1 40.7 41.4 42.0

32.0(b) 32.0(b) 32.0(b) 32.0(b) 32.0(b)

52 54 56 58 60

465.5(b) 485.5(b) 505.4(b) 530.1 558.0

42.6 43.3 43.9 44.6 45.2

586.5 615.7 645.5 675.9 707.0 787.5 872.0 960.5 t,053.0 1,149.5 1,250.0 1,463.0 1,692.0 1,937.0 2,198.0

45.8 46.5 47.1 47.8 48.4 50.0 51.6 53.2 54.8 56.4 58.0 61.2 64.4 67.6 70.8

Moment 365.9(b) 385.8(b)

End shear and end reaction (a)

2 3

16.0(b) 24.0(b)

4

32.0(b)

5

40.0(b)

6 7

48.0(b) 56.0(b)

8

64.0(b)

9 10

72.0(b) 80.0(b)

11 12 13 14 15 t6 17 18 t9 20 21 22 23 24 25

88.0(b) 96.0(b) 104.0(b) 112.0(b) 120.0(b) 128.0(b) 136.0(b) 144.0(b) 152.0(b) 160.0(b) t68.0(b) 176.0(b) 184.0(b) 192.0(b) 200.0(b)

32.0(b) 32.0(b) 32.0(b) 32.0(b) 33.0(b) 33.4(b) 33.8(b) 34.1(b) 34.4(b) 34.7(b) 34.9(b) 35.1(b) 35.3(b) 35.5(b)

62 64 66 68 70 75 80 85 90 95 100 110 120 130 140

26 27 28 29 30

208.0(b) 216.9(b) 226.8(b) 236.7(b) 246.6(b)

35.7(b) 35.9(b) 36.0(b) 36.1(b) 36.3(b)

150 160 170 180 190

2,475.0 2,768.0 3,077.0 3,402.0 3,743.0

74.0 77.2 80.4 83.6 86.8

31 32 33 34 35 36 37 38 39 40

256.5(b) 266.5(b) 276.4(b) 286.3(b) 296.2(b) 306.2(b) 316.1(b) 326.1(b) 336.0(b) 346.0(b)

36.4(b)

200 220 240 260 280 300

4,100.0 4,862.0 5,688.0 6,578.0 7,532.0 8,550.0

90.0 96.4 102.8 109.2 115.6 122.0

32.5(b)

36.5(b)

36.6(b) 36.9 37.2 37.5 37.8 38.2 38.5 38.8

(a) Concentrated load is considered placed at the support. Loads used are those stipulated for sheat (b) Maximum value determined by Standard Truck Loading. Otherwise the Standard Lane Loading governs.

App. A

HIGHWAY BRIDGES

632

LOADING—HS 20-44 (MS18) TABLE OF MAXIMUM MOMENTS, SHEARS, AND REACTIONS—

SIMPLE SPANS, ONE LANE Spans in feet; moments in thousands offoot-pounds; shears and reactions in thousands ofpounds. These values are subject to specification reduction for loading of multiple lanes. Impact not included.

2 3 4 5

Moment 8.0(b) 16.0(b) 24.0(b) 32.0(b) 40.0(b)

End shear and end reaction (a) 32.0(b) 32.0(b) 32.0(b) 32.0(b) 32.0(b)

Span 42 44 46 48 50

Moment 485.3(b) 520.9(b) 556.5(b) 592.1(b) 627.9(b)

End shear and end reaction (a) 56.0(b) 56.7(b) 57.3(b) 58.0(b) 58.5(b)

6 7 8 9 10 II 12 13 t4 15

48.0(b) 56.0(b) 64.0(b) 72.0(b) 80.0(b) 88.0(b) 96.0(b) 104.0(b) 112.0(b) 120.0(b)

32.0(b) 32.0(b) 32.0(b) 32.0(b) 32.0(b) 32.0(b) 32.0(b) 32.0(b) 32.0(b) 34.t(b)

52 54 56 58 60 62 64 66 68 70

663.6(b) 699.3(b) 735.1(b) 770.8(b) 806.5(b) 842.4(b) 878.1(b) 914.0(b) 949.7(b) 985.6(b)

59.t(b) 59.6(b) 60.0(b) 60.4(b) 60.8(b) 61.2(b) 61.5(b) 61.9(b) 62.1(b) 62.4(b)

16 17 18 19 20

128.0(b) 136.0(b) 144.0(b) 152.0(b) 160.0(b)

36.0(b) 37.7(b) 39.1(b) 40.4(b) 41.6(b)

75 80 85 90 95

1,075.1(b) 1,164.9(b) 1,254.7(b) 1,344.4(b) 1,434.1(b)

63.1(b) 63.6(b) 64.1(b) 64.5(b) 64.9(b)

21 22 23 24 25

168.0(b) 176.0(b) 184.0(b) 192.7(b) 207.4(b)

42.7(b) 43.6(b) 44.5(b) 45.3(b) 46.1(b)

100 110 120 130 140

1,524.0(b) 1,703.6(b) 1,883.3(b) 2,063.1(b) 2.242.8(b)

65.3(b) 65.9(b) 66.4(b) 67.6 70.8

26 27 28 29 30

222.2(b) 237.0(b) 252.0(b) 267.0(b) 282.1(b)

46.8(b) 47.4(b) 48.0(b) 48.8(b) 49.6(b)

150 160 170 180 190

2,475.1 2,768.0 3,077.1 3,402.1 3,743.1

74.0 77.2 80.4 83.6 86.8

31 32 33 34 35 36 37 38 39 40

297.3(b) 3t2.5(b) 327.8(b) 343.5(b) 361.2(b) 378.9(b) 396.6(b) 414.3(b) 432.1(b) 449.8(b)

50.3(b) 51.0(b) 51.6(b) 52.2(b) 52.8(b) 53.3(b) 53.8(b) 54.3(b) 54.8(b) 55.2(b)

200 220 240 260 280 300

4,100.0 4,862.0 5,688.0 6,578.0 7,532.0 8,550.0

90.0 96.4 t02.8 109.2 115.6 122.0

Span

(a) Concentrated load is considered placed at the support. Loads used are those stipulated for shear. (b) Maximum value determined by Standard Truck Loading. Otherwise the Standard Lane Loading governs.

APPENDIX B

TRUCK TRAIN AND EQUIVALENT LOADINGS 1935 SPECIFICATIONS AMERICAN ASSOCIATION OF STATE HIGHWAY OFFICIALS —

81 OH

a

Cr)

‘ii

I

N

tsTON~tJCK

I

I

2OTONTRUGK

I

jjTR~c~J

iSTON TRUCK p

30’

14’

30’

14’

14’

30’

0~ —~ ~Q

4.14’4 —

30’

H-20-35 LOADING 0

oj ~ mlv.rONTRL)cK I C) 30’j

30’

I

L2~I2~Tn~J p C)

14’

30’

f

mlTONTRtJCK

14’ 30’ 141 H-15-35 LOADING

TRUCK

TRAIN

j 1l~TONTRUCK j 30

14’

LOADING

CONCENTRATED LOADI18,OOO 126,000 LBS. LBS. FOR FOR MOMENT SHEAR 1’~’UNlFORM LOAD 640 LBS. PER LINEAR FOOT OF LANE H-20-35 LOADING CONCENTRATED LOAD

4

13,500 LBS. FOR MOMENT 9500 LBS. FOR SHEAR fr’ UNIFORM L OAD 480 LBS. PER LINEAR FOOT OF LANE

U—’

H-15-35 LOADING

EQUIVALENT LOADING LANE WIDTH 10 FEET 633

30’

APPENDIX C

0 (0

c\J

C’)

z

Z—J

tl~

~3O> C

o-Q~

0~ Q-Jc~~ LL