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CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES Published June 2008
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AMERICAN SEGMENTAL BRIDGE INSTITUTE 9201 N. 25"' Avenue, Suite 150B. Phoenix. Arizona 85021-2721 Tel: (602) 997-9964 Fax: (602) 997-9965 e-mail:
[email protected] web: www.asbi-assoc.org
©Copyright 2008 by the American Segmental Bridge Institute. 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 publisher.
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Billinger Berger lngeniEurbau GmbH Bibliothek
MASTER TABLE OF CONTENTS
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CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTERS 1.0-17.0 FHWA Post-Tensioning Tendon Installation and Grouting Manual
CHAPTER 1.0 INTRODUCTION AND OVERVIEW OF SEGMENTAL CONSTRUCTION
)
1.0
Introduction and Overview of Segmental Construction
3
1.1
Purpose
3
1.2
Advantages of Segmental Construction
3
1.3
Structure Types
3
1.3.1
Precast Segmental Span-by-Span
3
1.3.2
Precast Segmental Balanced Cantilever Bridges
5
1.3.3
Precast Segmental Progressive Placement
6
1.3.4
Precast Segmental Arches
7
1.3.5
Cast-In-Place Segmental Balanced Cantilever Bridges
8
1.3.6
Cast-In-Place Segmental Arches
1.3.7
Cast-In-Place Segmental Incremental Launching
10
1.3.8
Precast and Cast-in-Place Segmental Cable-Stayed Bridges
11
1.3.9
Heavy Segmental
13
1.3.9.1
Confederation Bridge, New Brunswick- Prince Edward Island, Canada
1.3.9.2 San Francisco- Oakland East Bay Skyway Bridge 1.4
Documentation of Design Assumptions in Contract Documents
9
13 15 17
CHAPTER 2.0 TERMINOLOGY
2.0 Terminology
3
2.1 General Terminology
3
2.2 Post-Tensioning and Grouting Terminology
8
CHAPTER 3.0 CONSTRUCTION OF PRECAST SPAN-BY-SPAN BRIDGES
3.0
Construction of Precast Segmental Span-by-Span Bridges
3
3.1
3
3.2
Introduction Advantages of Segmental Span-by-Span Bridges
6
3.3
Typical Span-by-Span Erection Sequence
8
3.4
Special Considerations
3.5
Safety
18
3.6
Summary
20
17
) Table of Contents, Chapters 1.0- 17.0 and Post-Tensioning Tendon Installation & Grouting Manual
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CHAPTER 4.0 CONSTRUCTION OF PRECAST BALANCED CANTILEVER BRIDGES 4.0
Construction of Precast Segmental Balanced Cantilever Bridges
4.1
Overview
3
4.1.1
Basics of the Technique
3
4.1.2
Typical Segments Configurations
4
4.1.3
Segment Details
5
4.1.3.1
Cantilever Tendon Anchorages
6
4.1.3.2 Continuity Anchors
7
4.1.3.3 Temporary Post-Tensioning
7
4.1.3.4 Permanent Ducts
7
4.1.3.5 Web Keys
9
4.1.3.6 Flange Keys Casting Yard and Transportation 4.2
9
4.2.1
9
Forms
'
3
9
4.2.2
Detailing and Workmanship
10
4.2.3
Geometry Control
13
4.3.4
13
4.3
Lifting Details Typical Erection Cycle
4.3.1
Overview
14
14
4.3.2
Epoxy
15
4.3.3
Temporary PT
16
4.3.4
Tendon Installation and Jacking
17
4.3.5
Grouting
18
4.4
Erection Equipment and Methods
19
4.4.1
20
4.4.2
Crane Beam and Winch
4.4.3
Erection Gantry
22
4.4.4
Hauler
27
4.5
Special Topics Surveying and Deflections
27
4.5.1 4.5.2
Pier Segments
28
4.5.2.1
)
21
27
Cast-in-Place
28
4.5.2.2 Precast Pier Segment
30
4.5.2.3 Precast Shell Expansion Joints 4.5.3
31 33
4.5.4
Mid-Span Closure
37
4.5.6
Temporary Access Openings
38
4.6
Engineering
38
4.6.1
Built-in Loads
38
4.6.2
Erection Loads
39
4.6.3
Cambers and Deflections
39
4.6.4
Temporary Post-Tensioning
39
Table of Contents, Chapters 1.0- 17.0 and Post-Tensioning Tendon Installation & Grouting Manual
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CHAPTER 5.0 CONSTRUCTION OF CAST-IN-PLACE BALANCED CANTILEVER BRIDGES
5.0 5.1 5.2
Construction of Cast-in-Place Balanced Cantilever Bridges Introduction Construction Methods
3 3 6
CHAPTER 6.0 INCREMENTAL LAUNCHING SEGMENTAL BRIDGES
6.0 6.1 6.2 6.3 6.4 6.5 6.6 6.7
Construction of Incremental Launching Segmental Bridges
3
Introduction
3
Advantages of Incremental Launching Segmental Bridges Characteristics of Incremental Launching Segmental Bridges Typical Construction Sequence Launching System and Equipment Summary Reference
4 6 12 13 18 18
CHAPTER 7 Special Requirements for Construction of Concrete Segmental Cable-Stayed Bridges
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7.0 7.1 7.2 7.3 7.3.1 7.3.2 7.3.3 7.4 7.4.1 7.4.2 7.4.3 7.4.4 7.5. 7.5.1 7.5.2 7.5.3 7.5.4 7.6 7.7 7.8 7.8.1 7.8.2 7.9
Cable-Stayed Bridges Introduction Cable-Stayed Structure Critical Construction Phases Deck, Stay Cable Stresses Unbalanced Loads Other Critical Construction Loads Geometry Control Casting Curves Geometry Control for Prescast Box Girder Segments Geometry Control for Cast-in-Place Box Girders Geometry Control for Cast-in-Place Flexible Decks Stay-Cable System Quality Control Stay-Cable Types Bearing Plate, Recess Pipe Installation Stay-Cable Pipe Installation Installation of Other Stay-Cable Components Control of Stay-Cable Forces Fatigue Testing Extradosed Bridges Design Concept Construction of Extradosed Bridges
Conclusion References
Notable Concrete Cable-Stayed Bridges in the United States
3 3 3 5 5 11 13 14 14 15 20 20 20 20 20 22 23 24 26 26 26 28 29 29 29
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CHAPTER 8.0 SEGMENTAL SUBSTRUCTURES
8.0 8.1 8.2 8.3 8.4 8.5
Segmental Substructures Introduction Project Examples Precasting Operations
Erection Operations Summary
3 3
3 7 10 11
CHAPTER 9.0 PRODUCTION OF PRECAST SEGMENTS
9.0 9.1 9.1.1 9.1.2 9.1.2.1 9.1.2.2 9.1.2.3 9.1.2.4 9.1.3 9.1.3.1 9.1.3.2 9.1.3.3 9.1.3.4 9.1.3.5 9.1.4 9.1.4.1 9.1.4.2 9.1.5 9.1.5.1 9.1.5.2 9.1.5.3 9.1.5.4 9.1.6 9.1.9.1 9.1.9.2 9.1.9.3 9.1.9.4 9.1.9.5 9.1.7 9.1.7.1 9.1.7.2 9.1.7.3 9.1.7.4 9.1.7.5 9.1.7.6 9.1.7.7 9.1.7.8
Segment Production
Casting Yard Planning and Setup Introduction Location Acreage Utilities Existing Buildings Water Access Existing Site Conditions Soil Conditions
Drainage/Storm Water Plan Wetlands Issues
Security Slip or Dock Conditions Receiving/Delivery Delivery of Segments Material Deliveries Site Preparation Local Permits-Developer Fees Grubbing and/or Clearing Grading-Drainage, Runoff Foundations
Procurement Forms Batch Plant Steam Generator
Cranes (Gantry Cranes, Tower Cranes and Segment Haulers) Auxiliary Equipment
Facilities Office Trailer Locations Form Locations
Rebar Jig Locations Warehouse, Material Storage Location
Steam Generator Location, Piping Requirements Portable Toilet Locations Temporary Fuel Storage Trash, Scrap, Recyclables
3 3 3 6 6 6 6 7 7 7 8 8 8 8 8 8 9 10 10 10 10 10 12 12 15 15 16 17 20 20 21 23 24 24 24 24 25
Table of Contents, Chapters 1.0 - 17.0 and Post-Tensioning Tendon Installation & Grouting Manual
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CHAPTER 9.0 PRODUCTION OF PRECAST SEGMENTS Continued
9.1.8 9.1.9 9.2 9.2.1 9.2.2 9.3 9.4 9.5 9.6 9.7 9.8 9.9 9.10 9.11 9.12 9.13 9.14 9.14.1 9.14.2 9.14.3 9.14.4 9.14.5
Post Casting Summary- Casting Yard Planning and Setup Long Line and Short Line Forms Long Line Casting Bed Short Line Casting Bed Match Casting Casting Curve Fabrication of Rebar Cage with Post-Tensioning Ducts and Hardware Installation of Post-Tensioning Ducts Handling the Prefabricated Rebar Cage Rebar Cage in Casting Cell Setting the Match Cast Segment Placing Concrete Finishing the Top Surface Curing
Forms
~ ~')\A. "'-~
J fri ~.s
Special Situations- Elevated Light Rail Construction Rail Construction LRT Electrification
Crossover Construction Grounding Requirements LRT Conclusion
25 26 27 27 33 37 38 39 41 41 42 42 43 45 46 47 50 50 52 52 53 55
CHAPTER 10.0 PROCEDURES FOR HANDLING TRANSPORTING AND ERECTING PRECAST SEGMENTS
10.0 10.1 10.1.1 10.1.2 10.1.3 10.2 10.2.1 10.2.2
Procedures for Handling, Transporting and Erecting Precast Segments
3 Methods of Lifting Precast Segments 3 Lifting Holes Cast in the Top Slab of Segments 3 Inserts Embedded in the Segment Webs and Protruding Above the Top Slab 4 Lifting Slings or C Hook Frame 5 Handling and Transporting of Precast Segments in Precast Yard 6 Handling precast segment from the new-cast position to the match-cast position 6 Handling and Transporting of Precast Segments from the Casting Area to the Storage Area
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 10.3.3 10.4 10.4.1
Transporting Precast Segments from the Precast Yard to the Erection Site Transporting Precast Segments via Water Using Barges Loading Transport
Unloading Transporting Precast Segments Off-site via Land Loading Transport Unloading Transporting Precast Segments On-site via Land Erection of Precast Segmental Bridges Factors for the Selection of Precast Segmental Bridge Erection Methods
6 11 11 11 12 12 14 14 14 15 15 19 19
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CHAPTER 10.0 PROCEDURES FOR HANDLING TRANSPORTING AND ERECTING PRECAST SEGMENTS Continued
10.4.2 10.4.2.1 10.4.2.1.1 10.4.2.1.2 10.4.2.1.3 10.4.2.1.4 10.4.2.1.5 10.4.2.1.6 10.4.2.2 10.4.2.2.1 10.4.2.2.2 10.4.2.2.3 10.4.2.2.4 10.4.2.3
Erection Methods for Precast Segmental Bridges Erection Methods for Span-by-Span Type Bridges Underslung Trusses with Crane on Ground or Barge Mounted on Water Erection on Underslung Trusses with Crane or Derrick/Lifter on Deck Erection with an Overhead Gantry Full Span Erection wtlh Winches I Strand Jacks Full Span Carrier I Erector Full Span Erection on Shoring Falsework Erection Methods for Balanced Cantilever Bridges Balanced Cantilever Erection by Crane on Ground or on Water Balanced Cantilever Erection by Overhead Gantries Balanced Cantilever Erection with Beam and Winch/Strand Jacks Balanced Cantilever Erection with Special Erectors Erection Methods Conclusion
21 22 22 24 25 27
28 29 30 30 32 34 36 37
CHAPTER 11.0 ERECTION DETAILS
11.0 11.1 11.1.1 11.1.1 11.1.2 11.1.2 11.1.3 11.1.3 11.1.4 11.1.4 11.1.5 11.1.5 11.1.6 11.1.6 11.1.7 11.1.7 11.1.8 11.1.8 11.2 11.3 11.4 11.5 11.6 11.7
Erection Details Permanent Post-Tensioning Anderson Technology Corporation- Transparent Sheathing Anderson Technology Corporation- Super Corrosion Protective (Supra Strand) AVAR Post-Tensioning Systems for Segmental Bridge Construction Single Plane/Multi Plane AVAR Post-Tensioning Systems for Segmental Bridge Construction Single Plane/Flat Anchorage DYWIDAG-Systems International- DYWIDAG Post-Tensioning Systems for Segmental Construction DYWIDAG-Systems International- DYWIDAG Post-Tensioning Systems for Segmental and CIP Construction Freyssinet Post-Tensioning Systems- Freyssinet Post-Tensioning Hardware for Segmental Bridges/G-Range Post-Tensioning Systems Freyssinet Post-Tensioning Systems- Freyssinet F-Range Post-
3 3 4
Tensioning Systems
11 12 13 14
Mexpressa -Jacks and Pumping Units Mexpressa -Anchorages and Couplers SDI Post-Tensioning Systems and Services SDI Type C Multistrand Anchorage/Type C4.6 Multistrand Anchorage/ Type D Multistrand Anchorage VSL Segmental Bridge Post-Tensioning Systems- Anchorage VSL Type ECI/Type ES/Type E/PT-Pius Duct System VSL Segmental Bridge Post-Tensioning Systems- Anchorage VSL Type SAIVSLAB+® System Williams Form Engineering Corporation- The Williams System Williams Form Engineering Corporation-150 KSI All-Thread Bar Temporary Post-Tensioning Post-Tensioning Safety Issues Lifting Segments for Erection Temporary Supports Midspan Closure Construction Schedule and Sequence
Table of Contents, Chapters 1.0 - 17.0 and Post-Tensioning Tendon Installation & Grouting Manual
5 6 7
8 9 10
15 16 17 18 19 20 23 30 31 32 33
6 of9
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CHAPTER 12.0 EPOXY JOINTING, DUCT COUPLER DEVICES, AND PREPACKAGED GROUT 12.0 Epoxy Jointing, Duct Coupler Devices, and Prepackaged Grout
Purposes of Epoxy Types and Application of Epoxy
12.3 12.3.1
FREYSSINET Post-Tensioning Systems
6 7
12.3.2 12.3.3 12.4 12.4.1
VSL Segmental Duct Coupler
8
12.4.1
BASF Construction Chemicals- Building Systems Epoxy and Prepackaged Grout for Segmental Bridge Construction
12.4.2 12.4.3
SIKA Corporation Epoxy Resin for Segmental Bridge Construction
14 15
SIKA Corporation Prepackaged Grouts for Segmental Bridge Construction
16
Duct and Duct Coupler Devices
General Technologies, Inc. Precast Segmental Duct and Duct Coupler Prepackaged Grout
CHAPTER 13.0 GEOMETRY CONTROL 13.0 Geometry Control
13.1 13.2 13.3 13.4 13.5 13.6 13.7 13.8 13.9 13.9.1 13.9.2
General Casting Cell Geometry Control System Tools Used for Geometry Control Geometry Control of the First Pier Segment Field Survey Checking During Erection Systematic Error Achieved Profiles Pier Shaft Segments Temperature Effects Temperature Expansion and Contraction Temperature Gradient
CHAPTER 14.0 BEARINGS AND EXPANSION JOINTS 14.0 Bearings and Expansion Joints
14.1
Bearings
14.1.1 14.1.2 14.1.3
Bearing Installation
14.1.4 14.1.5
Temperature Adjustment
14.2 14.2.1 14.2.2 14.2.3 14.2.4 14.2.5 14.2.5 14.2.6 14.2.6 14.2.7 14.2.7
Mortar Pads Horizontal-Position of Bearings Direction of Movement Expansion Joints
,-'
9 10 13
3 3 7 12 13 13 14 15 15 15 15 18
3 3 3 6 6 6 6
Expansion Joints Supplied by Freyssinet LLC
7 7 8 9 10 12 13 14 15
Bearings and Expansion Joints Supplied by Watson Bowman Acme Corporation
16
Bearings and Expansion Joints Supplied by Watson Bowman Acme Corporation
17
Strip Seal Systems Molded, Steel Reinforced Rubber Cushion Bolt-Down Systems (Transfiex or Wabofiex) Modular Joint Systems Finger Joints Bearings and Expansion Joints Supplied by The D.S. Brown Company Bearings and Expansion Joints Supplied by The D.S. Brown Company Expansion Joints Supplied by Freyssinet LLC
Table of Contents,' Chapters 1.0 - 17.0 and Post-Tensioning Tendon Installation & Grouting Manual (
3 3
BASF Construction Chemicals- Building Systems Epoxy and Prepackaged Grout for Segmental Bridge Construction
)
3
12.1 12.2
i
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CHAPTER 15.0 LESSONS LEARNED
15.0
Lessons Learned
3
15.1.0
General
3
15.2.0
Design Lesson Learned
4
15.2.1
Reinforcing Details
4
15.2.2
Tendon and Duct Detailing
4
15.2.3
Cracking
6
15.2.4
Designing for Construction Tolerance
7
15.2.5
Principal Stresses and Web Shear
7
15.2.6
Flange Shear Stresses
7
15.2.7
Asymmetric Sections and Rotated Principal Axes
9
15.2.8
Shear Distribution of Multiple Webs
9
15.2.9
Shear Lag
9
15.2.10 Combination of Transverse Bending and Shear
10
15.2.11 Built-in Loads
10
15.2.12 Tendon Losses
10
15.2.13 Bottom Slab Drainage Details
10
15.2.14 Inspection Access
11
15.3.0
Construction Lesson Learned
12
15.3.1
12
15.3.2
General Equipment Requirements
15.3.3
Construction Loads
12
15.3.4
Truss Stability
13
15.3.5
Bearing of Truss Supports Warping Under Concentrated Loads
14
15.3.6 15.3.7
Out-of-Balance Moments
14
15.3.8
Alignment and Geometry Problems
14
15.3.9
Geometry Control in Gore Regions
15
12
14
15.3.10
Fit of Match Cast Segments
15
15.3.11
Steam Curing and Warping
15
15.3.12
Short Tendon Elongations
16
15.3.13
Tendon Blockages
16
15.3.14
Tendon Pop-out
16
15.3.15 Epoxy Not Setting
18
15.3.16 Freezing of Water in Ducts and Recess Pockets
18
15.4.0
19
References
CHAPTER 16.0 CONSTRUCTION ENGINEERING & INSPECTION (CEI) OF SEGMENTAL CONSTRUCTION
16.0
Project Site Roles
2
16.1
Motivation of Stakeholders
3
16.2
CEI Early Involvement
4
16.3
Remote Precast Yard
4
16.4
16.7
Preconstruction Conference Engineering Submittals, Shop Drawings, RFis Technical Workshops I Submittals I Format Critical Issues early on at Precast Yard
16.8
Concrete Mix Designs
16.5 16.6
4 4 5 5
J
5
Table of Contents, Chapters 1.0 - 17.0 and Post-Tensioning Tendon Installation & Grouting Manual
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CHAPTER 16.0 CONSTRUCTION ENGINEERING & INSPECTION (CEI) OF SEGMENTAL CONSTRUCTION Continued
16.9 16.10 16.11 16.12 16.13 16.14 16.15 16.16 16.17 16.18 16.19 16.20
Casting Yard Quality Control/ Geometry Control
Review of Erection Procedures Confirmation of Erection Procedures Post Tensioning and Grouting
Bearings, Expansion Joints and Seismic Devices Highway vs. Rail Bridges Record Keeping I As-Builts Safety
Environmental Issues Claims and Changes Successful Project Ingredients Summary
5 6 6 6 7 7 7 7 8 8 8 9
CHAPTER 17.0 CONSTRUCTION INSPECTION GUIDELINES FOR SEGMENTAL CONCRETE BRIDGES
)
17.1 17.1.1 17.1.2 17.2 17.3 17.4 17.5 17.6 17.7 17.8 17.9 17.9.1 17.9.2 17.9.3 17.10 17.11 17.12 17.13 17.14 17.15 17.16 17.17 17.18 17.19 17.20 17.21 17.22 17.23
Recommended Practice for Initial Inspection of Forms
Form Dimensions and Tolerances Form Operation Recommended Practice for Daily Inspection of Forms Recommended Practice for Inspection of Cut and Bent Rebar Recommended Practice for Inspection of Rebar Cages
3 3 5 7 8 11
Recommended Practice for the Initial Inspection and Storage of Post-Tensioning Hardware 15 Recommended Practice for Inspection of Post-Tensioning Hardware In the Reinforcement Cage 17 Recommended Practice for Resolution of Rebar Conflicts
18 Recommended Practice for Inspecting Post-Tensioning Hardware in the Form 20 Recommended Practice for Inspection of the Setting of Matchcast Segments 21 On-Site Hardware 21 Measuring Instruments 22 Observations in the Casting Cell 23 Recommended Practice for Concreting Segments 26 Recommended Practice for Inspection of Curing of Segments 28 Recommended Practice for Inspection of Stripping Forms and Bond Breaking 29 Recommended Practice for Inspection of Segment Handling in the Casting Yard 30 Recommended Practice for Inspection of Repairs Made to Segments 31 Recommended Practice for Inspection of Segment Storage 33 Recommended Practice for Inspection of Segments for Payment 34 Recommended Practice for Inspection of Segment Transportation 35 Recommended Practice for Inspection of Erection Equipment 36 Recommended Practice for Inspection of Falsework 37 Recommended Practice for the Inspection of Epoxy Joints 38 Recommended Practice for Tendon Stressing 40 Recommended Practice for Inspection of Grouting 40 Recommended Practice for Inspection of Cast-in-Place Segmental Structures 40
FHWA Post-Tensioning Tendon Installation and Grouting Manual
Table of Contents, Chapters 1.0 - 17.0 and Post-Tensioning Tendon Installation & Grouting Manual
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Construction Practices Handbook For Concrete Segmental and Cable-Supported Bridges ACKNOWLEDGEMENTS In addition to the acknowledgements of individuals who were primary authors of chapters of the First Edition, the following individuals were primarily responsible for writing or revising chapters of the second edition: Chapters 2 & 11
Post-Tensioning Terminology and Post-Tensioning Safety Shahid Islam, Dywidag-Systems International USA, Inc.
Chapter 3
Construction ofPrecast Segmental Span-by-Span Bridges Jim Schneiderman, PCL Civil Constructors, Inc.
Chapter 4
Construction ofPrecast Segmental Balanced Cantilever Bridges Ben Soule, International Bridge Technologies, Inc. David Goodyear, T. Y. Lin International, Inc. Scott McNary, McNary, Bergeron Associates, Inc.
Chapter 5
Construction of Cast-in-Place Balanced Cantilever Bridges Sean Bush, PCL Civil Constructors, Inc.
Chapter 6
Construction of Cast-in-Place Incrementally Launched Bridges Marco Rosignoli, HNTB Corporation Takahiro Kakuta, PSM Construction, USA, Inc.
Chapter 7
Special Requirements for Construction of Concrete Segmental Cable-Supported Bridges Daniel Tassin, International Bridge Technologies, Inc.
Chapter 9
Production ofPrecast Segments Arthur Palmer, Consultant
Chapter IO
Procedures for Handling Transporting and Erecting Precast Segments Elie Homsi, Flatiron Constructors, Inc. Riccardo Castracani, DEAL/Rizzani De Becher USA
Chapter 13
Geometry Control Alan Moreton, Corven Engineering, Inc.
)
Lessons Learned
Chapter I5
Chapter I6
)
Cliff Freyermuth, ASBI Ben Soule, International Bridge Technologies, Inc. Ralph Salamie, Kiewit Pacific Company Construction Engineering Inspection ofSegmental Construction Ian Hubbard, Parsons Brinckerhoff, Inc. Thomas DeHaven, FIGG John W. Jordan, Earth Tech, Inc.
Acknowledgements (First Edition)
"A Guide to the Construction of Segmental Bridges" developed by and for the Florida Department of Transportation; October 1989, was used by the American Segmental Bridge Institute Construction Practices Committee as a source document in the development of the "Guidelines for Construction of Segmental Concrete Bridges" presented in this publication.
Contributions to the Handbook by individuals who were primary authors of chapters of this section of the manual are acknowledged as follows:
Chapter 3
Construction of Precast Segmental Span-by-Span Bridges - R. Kent Montgomery, FIGG
Chapter4
Construction of Precast Segmental Balanced Cantilever Bridges -David Jeakle, URS Corporation
Chapter 5
Construction of Cast-in-Place Balanced Cantilever Bridges -Teddy Theryo, Parsons Brinckerhoff, Inc.
Chapter 13
Segmental Substructures - R. Kent Montgomery, FIGG
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ASBI Construction Practices Committee May2008
)
JOHN D. ARMENI, Chair Anneni Consulting Services, LLC Crossings at Three Bridges 4411 Suwanee Dam Road, Suite 750 Suwanee, GA 30024 Phone: (770) 904-4178 Fax: (770) 904-3671 Cell (404) 414-3743
DAVID GOODYEAR Vice President T. Y. Lin International 1115 W. Bay Drive NW, Suite 206 Olympia WA 98502 (360) 754-0544 Fax: (360)754-1714 e-mail:
[email protected]
e-mail:
[email protected] SEAN BUSH PCL Civil Constructors, Inc. 2804 E. Jackson Street Orlando, FL 32803 Cell: (407) 896-5960 (407) 896-5963 e-mail:
[email protected]
ELIE H. HOMSI Vice President Engineering Services Flatiron Constructors, Inc. 100901-25 Frontage Road Longmont CO 80504 (720) 49+8134 Fax (720) 494-8150 e-mail:
[email protected]
DAN CABELLO
IAN HUBBARD
Bayshore Concrete Products Corporation
Parsons Brinckerhoff Construction Services
POB230 Cape Charles, VA 23310 (757) 331-2300 (757) 331-2501 e'mail :
[email protected]
15430 35th Ave, South Tukwila, WA98!88 (206) 3705555 (206) 444-6371 E-mail:
[email protected]
RICCARDO CASTRACANI DEAL/Rizzani de Eccher, USA 2999 NE 191st Street, Suite 901 Aventura, FL 33180 (305) 932-9700 Fax: (305) 932-9550
SHAHIDUL ISLAM, PH.D. Dywidag-Systems International USA. Inc. PT Engineering Unit 320 Marmon Drive Bolingbrook, IL 60440 ( 630) 972-4028 Fax: (630) 739-1405 E-mail: Shahid.islam@dsiamericacom
e-mail: rcastracani@rdeusanet TOM DeHAVEN FIGG 1585 Thomas Center Drive, Suite 106 Eagan, MN 55122 (651) 251-3444 Fax: (651) 251-3445 e-mail:
[email protected] GOWEN DISHMAN HNTB c/o 3408 S. Lakeshore Drive Lake Village, AR 71653 662-347-6506
[email protected] ANDREW A. GHOFRANI, P.E. Design/Build Manager Granite Construction, Inc. 585 W. Beach Street, Building #I Watsonville, CA 95076 (831)728-7548 Fax: (831) 728-7513 e-mail:
[email protected]
) "
TAKAHIRO KAKUTA PSM CONSTRUCTION USA, INC. 111 Anza Blvd., Suite 415 Burlingame, CA 94010 (650) 344-9109 Fax: (650) 344-9199 e-mail :
[email protected] KEEFER, MARK VSL 282 Alpine Drive Front Royal, VA 22630 Fax: (703) 451-0862 Mobile: (571) 437-3399 e~mail:
[email protected] RICKLAIL Southern Fonns. Inc. 445 Hales Bar Road Guild, TN 3 7340 (423) 942-7000 Fax: (423) 942-1902 e-mail:
[email protected]
ASBI Construction Practices Committee May2008 MYINTLWIN
FHWA Office ofBridge Technology lllBT, Room 3203, 400 7"' Street, SW Washington, DC 20590 (202) 366-4589 Fax: (202) 366-3077
ARTIIUR PALMER 603 Hudson River Road POBox248 Waterford, NY 12188 (H) 518-235-3647 (C) 518-810-6886 e-mail:
[email protected]
e-mail:
[email protected] RALPH SALAMIE SCOTT MCNARY McNary Bergeron & Associates 565 Burbank Street Suite A Broomfield, CO 80020 (CO .office only) (860) 388-2267 Fax: 860-388-2268
e-mail:
[email protected] SAM! MEGALLY PBS&J 9275 Sky Park Court, Suite 200 San Diego, CA 92123 (858) 514-1035 Fax: (858) 514-1001 e-mail:
[email protected]
MARK MILICI Dywidag Systems International, USA, Inc. 525 Wanaque Avenue, Suite LLI Pompton Lakes, NJ 07442-1833 (973) 276-9222 Fax: (973) 276-9292 e-mail:
[email protected] ALAN J. MORETON
Corven Engineering, Inc. 2882 Remington Green Circle Tallahassee, FL 32308 (850) 386-6800 Fax: (850) 386-9374
e-mail:
[email protected] STEVE PABST
Watson Bowman Acme-Corporation - A BASF Company 95 Pineview Drive Amherst, NY 14228 (716) 691-7566 Fax: (716) 691-9239 e-mail: steve.pabst@basfcom
Kiewit Pacific 2200 Columbia House Blvd. Vancouver, W A 98661 (360) 693-1478 Fax: (360) 693-5582 e-mail:
[email protected] JIM SCHNEIDERMAN PCL Civil Constructors, Inc. 3810 Northdale Blvd., Suite 200 Tampa, FL 33624 (813) 264-9500 Cell: (813) 781-0047 e-mail:
[email protected] BEN SOULE
Intemationa1 Bridge Technologies, Inc. 9325 Sky Park Court, Suite 320 San Diego, CA 92123 (858) 566-5008 Fax:.(.858) 566-1220
e-mail:
[email protected] EDWARD TRIPODI ETIPTC 3430 Tumingwind Lane Winter Garden, Fl. 34787 (612) 328-7778 e-mail:
[email protected] JOHN WHITE
Williams Form. Engineering Corp. 8165 Graphic Drive, N.E. Belmont, MI 49306-9448 (616) 866-0815 Fax: (616) 866-1810
e-mail:
[email protected] CLIFFORD L. FREYERMUTH, Facilitator ASBI 9201 N. 25th Avenue, Suite 150B Phoenix, AZ 85021 (602) 997-9964 Fax: (602) 997-9965 e-mail:
[email protected]
) 2
DISCLAIMER This publication is intended for the use of professionals competent in evaluating the significance and limitation of its contents and who will accept responsibility for the application of the materials it contains. American Segmental Bridge Institute makes no warranty regarding the recommendations contained herein, including warranties of quality, workmanship or safety, express or implied, further including, but not limited to,. implied warranties or merchantability and fitness for a particular purpose.
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INCLUDING
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REFUND OF THE PURCHASE PRICE OF THIS PUBLICATION. The incorporation by reference or quotation of material in this publication in any specifications, contract documents, purchase orders, drawings or job details shall be done at the risk of those making such reference or quotation and shall not subject the American Segmental Bridge )
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[email protected] Website: www.asbi-assoc.org
)
)
TABLE OF CONTENTS CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 1.0 INTRODUCTION AND OVERVIEW OF SEGMENTAL CONSTRUCTION
1.0
Introduction and Overview of Segmental Construction
3
1.1
Purpose
3
1.2
Advantages of Segmental Construction
3
1.3
Structure Types
3
1.3.1
Precast Segmental Span-by-Span
3
1.3.2
Precast Segmental Balanced Cantilever Bridges
5
1.3.3
Precast Segmental Progressive Placement
6
1.3.4
Precast Segmental Arches
7
1.3.5
Cast-In-Place Segmental Balanced Cantilever Bridges
8
1.3.6
Cast-In-Place Segmental Arches
9
1.3.7
Cast-In-Place Segmental Incremental Launching
10
1.3.8
Precast and Cast-in-Place Segmental Cable-Stayed Bridges
11
1.3.9
Heavy Segmental
13
1.3.9.1 Confederation Bridge, New Brunswick- Prince Edward Island, Canada
13
1.3.9.2 San Francisco- Oakland East Bay Skyway Bridge
15
1.4
17
Documentation of Design Assumptions in Contract Documents
Chapter 1.0 Introduction and Overview of Segmental Construction
1 of 17
TABLE OF FIGURES CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 1.0 INTRODUCTION AND OVERVIEW OF SEGMENTAL CONSTRUCTION
Figure 1.1
Erection Truss in Place to Receive Segments
4
Figure 1.2
Erecting Segments on the Glenwood Canyon Project
4
Figure 1.3
Common Segment Installation Methods
5
Figure 1.4
Erection of Cantilever N-E5 with Segment Erector. Cantilever W-N 10 in the Foreground
5
Figure 1.5
Erection Scheme for Progressive Placement
6
Figure 1.6
Construction of the Linn Cove Viaduct, NC
6
Figure 1.7
Construction of Natchez Trace Arch Bridge
7
Figure 1.8
Placement of Keystone of Natchez Trace Arch Bridge
7
Figure 1.9
Construction of Cast-in-Place Balanced Cantilever Bridges
8
Figure 1.10
Construction of the Crooked River Bridge Arch, OR
9
Figure 1.11
Hoover Dam Bypass Arch Bridge Rendering
9
Figure 1.12
Incremental Launching
10
Figure1.13
Launching Nose on Bellaire Beach Bridge, Tampa, FL (Photo courtesy of VSL)
10
Launching Equipment for the Bellaire Beach Bridge, Tampa, FL (Photo courtesy of VSL)
11
Figure 1.15
C & D Canal Bridge, DE
12
Figure 1.16
Sunshine Skyway Bridge, Tampa, FL
12
Figure 1.17
Dames Point Bridge, Jacksonville, FL
13
Figure 1.18
Confederation Bridge Casting Yard
13
Figure 1.19
Erection of 660 feet, 7,500 ton Cantilever
14
Figure 1.20
Long Line Casting Form- San Francisco-Oakland
Figure 1.14
East Bay Skyway Bridge Figure 1.21
Figure 1.22 Figure 1.23
15
800-ton Segment Transporter- San Francisco Oakland East Bay Skyway Bridge
15
Segment Storage- San Francisco-Oakland East Bay Skyway Bridge
16
San Francisco-Oakland Skyway Bridge, Erection of First Segment, July 26, 2004
16
) Chapter 1.0 Introduction and Overview of Segmental Construction
2ofl7
CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES 1.0 1.1
Introduction and Overview of Segmental Construction Purpose The purpose of this handbook is to provide guidance for construction of segmental concrete bridges. Although the segmental construction concept is generally very simple, the construction technology involved is in numerous ways more demanding than that required for other types of bridge construction. The use of segmental concrete bridge construction has grown rapidly, which has sometimes led to involvement of personnel with limited experience with segmental technology in the construction process. This handbook is intended to provide a basic understanding of segmental construction technology with the goal of facilitating the construction process, avoiding some problems previously encountered, and reducing delays and costs caused by concern over non-critical construction issues, or lack of understanding of critical issues.
1.2
Advantages of Segmental Construction Segmental concrete bridge construction offers the advantages of industrialized, repetitive construction procedures, which contribute to reductions in cost and construction time, as well as improved quality control. Segmental bridge construction offers maximum protection to the bridge environment, and provides for maintenance of highway and railway traffic at the construction site. Segmental bridges are easily adaptable to curved highway aligument and also provide aesthetic advantages. The advantages of segmental bridges have led to their widespread use for urban viaducts and interchanges, rapid transit bridges, bridges over water, and for very long bridges built using span-by-span construction. Finally, segmental construction extends the span range of concrete bridges to 550 feet using precast segments, and to over 800 feet using cast-in-place segments. Use of cable-stayed bridge construction (not covered in this handbook) permits the use of concrete segmental spans of more than 1,500 feet.
1.3
Structure Types
1.3.1
Precast Segmental Span-by-Span Precast segmental span-by-span bridges have normally been used for a span range of 80 to 150 feet. When segments can be transported by water spans of 180 feet are feasible. Span-by-span bridges provide very high speed of construction, and can be constructed over or parallel to existing highways with little or no impact on traffic. Span-by-span bridges are most often constructed using an erection truss under the segments as shown in Figures 1.1 and 1.2. Overhead erection gantrys have also been used for span-by-span construction.
) Chapter 1.0 Introduction and Overview of Segmental Construction
3 of 17
Figure 1.1- Erection Truss in Place to Receive Segments
Figure 1.2- Erecting Segments on the Glenwood Canyon Project
J Chapter 1.0 Introduction and Overview of Segmental Construction
4 of 17
')
1.3.2
Precast Segmental Balanced Cantilever Bridges Precast segmental balanced cantilever bridges are presently used in the U.S. for spans up to 440 feet When circumstances permit the use of "heavy" segmental construction, spans as long as 820 feet have been built in balanced cantilever. The balanced cantilever construction process involves placing segments progressively on alternate sides of a pier. As shown in Figure 1.3, segments can be erected by land or barge-mounted cranes, by deck-mounted lifting equipment, or by an overhead gantry. Erection speed using cranes typically varies between 2 to 4 segments per day per crane. A mobile rubber-tired segment erector used in 2002 in construction of the Dallas High Five Interchange is shown in Figure 1.4.
'.' = II I
II I I I =
!
!
I
,.
I! l
''1''1'''1'1~
Figure 1.3- Common Segment 1nstallation Methods
)
Figure 1.4- Erection of Cantilever N-ES with Segment Erector. Cantilever W-N 10 in the Foreground
Chapter 1.0 Introduction and Overview of Segmental Construction
5 of 17
1.3.3
Precast Segmental Progressive Placement Precast segmental progressive placement may be used for spans ranging from I 00 to 300 feet. This method
of construction has been applied or considered in environmentally sensitive locations where construction access is restricted to one or both ends of the bridge. A sketch of the erection scheme is shown in Figure 1.5, and a construction view of the Linn Cove Viaduct is presented in Figure 1.6.
Figure 1.5- Erection Scheme for Progressive Placement
Figure 1.6- Construction of the Linn Cove Viaduct, NC
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. \
1.3.4
Precast Segmental Arches
I
Construction of the precast segmental arch spans of the Natchez Trace Parkway Bridge in Tennessee is illustrated by Figures 1.7 and 1.8. The arch spans range to 582 feet. Segment erection is supported by tiebacks to piers, or tie-backs anchored at ground anchors at the abutments. The Natchez Trace Parkway Bridge deck was constructed utilizing balanced cantilever construction with spans ranging from 90 to 246 feet.
Figure 1.7 - Construction of Natchez Trace Arch Bridge
Figure 1.8- Placement of Keystone of Natchez Trace Arch Bridge Chapter 1.0 Introduction and Overview of Segmental Construction
7 of 17
1.3.5
Cast-in-Place Segmental Balanced Cantilever Bridges Cast-in-place balanced cantilever bridges are used for spans ranging from 350 to 850 feet, although spans in excess of 700 feet are rare. Typical cast-in-place cantilever bridge construction is illustrated in Figure 1.9. As shown in the figure, the construction of cast-in-place cantilever bridges is based on the use ofform travelers which support the concrete for segments that typically vary between 10 and 20feet long, although longer lengths are possible. An average form traveler, for a single-cell box girder weighs approximately 160-180 kips. Extreme weights for large form travelers can exceed 250 kips. Typically, segments are constructed in each form traveler on a 5-day cycle. However, 2-, 3- and 4-day cycles per segment have been achieved in some cases. As illustrated by Figure 1.9e, cast-in-place segmental construction utilizing tie-backs can be used for construction of segmental arches.
d)
Figure 1.9- Construction of Cast-in-Place Balanced Cantilever Bridges
Chapter 1.0 Introduction and Overview of Segmental Construction
8 of 17
1.3.6
Cast-in-Place Segmental Arches Cast-in-place segmental construction for the 535 feet arch span of the Crooked River Bridge in Oregon in 2000 is shown in Figure 1.1 0. A rendering of the Hoover Dam Bypass Bridge with a segmental arch span of 1,090 feet is presented in Figure 1.11. Construction of the Hoover Dam Bypass Bridge began in the Fall of 2004. The construction schedule calls for completion in June of 2008. The Hoover Dam Bypass Bridge design includes an alternate for precast segmental construction of the arches.
FiJ?ure 1.10- Construction of the Crooked River BridJ?e Arch, OR
)
Figure 1.11- Hoover Dam Bypass Arch Bridge Rendering
Chapter 1.0 Introduction and Overview of Segmental Construction
9 ofl7
1.3.7
Cast-in-Place Segmental Incremental Launching Cast-in-place segmental incremental launching involves construction of segments in a casting bed at one or both abutments, and pushing the segments across the piers by means of hydraulic jacks. Spans may range to about 350 feet, but longer spans may require use of temporary mid-span supports. The principle of incremental launching is illustrated in Figure 1.12. Figures 1.13 and 1.14 illustrate incremental launching of the Bellaire Beach Bridge in Tampa, Florida in 2008. Detailed description of construction of incrementally launched concrete bridges is presented in Chapter 6.0. A steel launching nose is attached to the first segment to reduce moments and stresses during launching as shown in Figure 1.13 with reference to the Bellaire Beach Bridge in Tampa, Florida. Launching equipment for the Bellaire Beach Bridge is shown in Figure 1.14.
l Figure 1.12 -Incremental Launching
Figure 1.13 -Launching Nose on Bellaire Beach Bridge, Tampa, FL (Photo courtesy of VSL)
Chapter 1.0 Introduction and Overview of Segmental Construction
10 of 17
Figure 1.14 -Launching Equipment for the Bellaire Beach Bridge, Tampa, FL (Photo courtesy ofVSL)
1.3.8
Precast and Cast-in-Place Segmental Cable-Stayed Bridges Precast and cast-in-place cable-stayed bridges are discussed in Chapter 7.0. In addition, both precast segmental construction technology and cast-in-place segmental technology as discussed in this Handbook are applicable to construction of concrete cable-stayed bridges. Examples of U.S. cable-stayed bridges are the C&D Canal Bridge in Delaware with precast segments and a main span of750 feet (Figure 1.15), the Sunshine Skyway Bridge in Tampa, Florida with precast segments and a main span of I ,200 feet (Figure 1.16), and the Dames Point Bridge in Jacksonville, Florida with cast-in-place segments (edge girder, deck and floor beam) and a main span of I ,300 feet (Figure 1.17).
Chapter 1.0 Introduction and Overview of Segmental Construction
11 ofl7
Figure 1.15- C & D Canal Bridge, DE
Figure 1.16- Sunshine Skyway Bridge, Tampa, FL
Chapter 1.0 Introduction and Overview of Segmental Construction
12ofl7
Figure 1.17- Dames Point Bridge, Jacksonville, FL
1.3.9
Heavy Segmental
1.3.9.1 Confederation Bridge, New Brunswick- Prince Edward Island, Canada For the Confederation Bridge between New Brunswick and Prince Edward Island, Canada, massive segmental cantilevers 660 feet long and weighing 7,500 tons were assembled at a casting yard adjacent to the bridge site (Figure 1.16), and erected by a huge floating catamaran in one piece (Figure 1.17).
)
Figure 1.18 - Confederation Bridge Casting Yard
Chapter \.0- Introduction and Overview of Segmental Construction
13ofl7
Figure 1.19- Erection of 660 foot, 7,500 ton Cantilever
\
) Chapter 1.0 Introduction and Overview of Segmental Construction
14ofl7
1.3.9.2 San Francisco - Oakland East Bay Skyway Bridge The Skyway portion of the San Francisco Oakland Bay Bridge, East Span Replacement consists of dual precast segmental concrete structures, measuring 6,900 feet in length, and two times 82 feet in width. The typical span length is 525 feet, and 28 cantilevers will be constructed using 452 precast segments. Typical segments are 25 feet long, 82 feet wide, and the maximum segment weight is 800 tons. Figure 1.18 shows the long .line casting form for the segments, Figure 1.19 shows the 800-ton segment transporter, and segment storage is illustrated in Figure 1.20. Segments are delivered on barges since the entire structure is over water. The erection equipment consists of self-launching beams and hydraulic winches. The size and weight of these segments has made the design and fabrication of this erection equipment unique and challenging. All lifting and hydraulic equipment has been factory tested and calibrated. In addition, each SLED will be load tested to 125 percent of the heaviest segment weight. The Skyway Structure consists of 28 cantilevers, and each cantilever has up to nine segments on each side. The speed of moving from cantilever to cantilever is more important than the lifting and launching speed for each segment. The two lifters that make up a SLED are fully self-contained, and each lifter can be moved to the next cantilever in a single pick as a complete unit. Figure 1.21 shows erection of the first segment on July 26, 2004.
Figure 1.20- Long Line Casting Form- San Francisco-Oakland East Bay Skyway Bridge
) .. /
Figure 1.21 - 800- ton Segment Transporler- San Francisco Oakland East Bay Skyway Bridge Chapter 1.0 Introduction and Overview of Segmental Construction
15 of 17
Figure 1.22- Segment Storage- San Francisco-Oak/and East Bay Skyway Bridge
Figure 1.23 - San Francisco-Oakland Skyway Bridge, Erection of First Segment, July 26, 2004
) Chapter 1.0 Introduction and Overview of Segmental Construction
16 of 17
1.4
Documentation of Design Assumptions In Contract Documents Adequate documentation of the assumptions made during the design phase regarding the construction methods and erection loads is essential to contractors. To deliver a cost effective and successful project, the construction sequence, schedule, methodology and equipment assumed during the design phase should be clearly and thoroughly presented in the contract plans. Maximum leeway for contractor modifications with regards to means and methods of construction should be provided in specifications; however, the basic system should be clearly presented to facilitate the receipt of accurate and responsive bids. Given the traditional method of separating design from construction, and further considering the relatively short bid preparation time, contractors must be presented with a scheme that works and has no hidden costs that become evident after the project has been awarded. Problems have occurred on segmental projects where construction loads were underestimated or misrepresented. The results were that the required strengthening of the permanent structure for temporary conditions led to additional costs and claims. When designing a segmental bridge, it is the designer's responsibility to outline the design, method of constructions f!Ild equipment used as the assumption for the design. With the assumptions clearly stated, the contractor tan re-engineer the structure, if need be, to suit his needs/experience with confidence, which leads to competitive bids.
) Chapter 1.0 Introduction and Overview of Segmental Construction
17 of 17
)
)
TABLE OF CONTENTS
CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 2.0 TERMINOLOGY 2.0 Terminology
3
2.1 General Terminology
3
2.2 Post-Tensioning and Grouting Terminology
8
) Chapter 2.0- Terminology
Page I of 10
TABLE OF FIGURES
CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 2.0 TERMINOLOGY
Figure 2.1 -Segmental Bridge Components
5
Figure 2.2 - Segment Features
5
Figure 2.3- Diabolo Details
6
Figure 2.4- Deviation Trumpet Details
7
Figure 2.5 Tendon Details
10
) Chapter 2.0- Terminology
Page 2 of 10
2.0 Terminology 2.1 General Terminology Anchorage Block- Build-out io the web, flange, or web-flange junction to provide area for one or more tendon anchorages (Figure 2.2). Balanced Cantilever Erection - This is an erection method where segments are erected alternatively on either side of the pier in cantilever up to the point where a cast-io-place closure is made with the previous cantilever or existing side span structure (Chapter 4.0) Beam and Winch - Custom made erection equipment consisting of a longitudinal beam fitted with lifting pulleys, tackle and winches which is attached to the end of a cantilever and lifts up the segments. After erecting a segment, the equipment is advanced for erection of the next segment. This equipment is used with balanced cantilever or progressive cantilever erection (Figure 4.3). Box Girder or Box Pier- Box shaped structural member used for bridge superstructures and piers as shown in Figure 2.2. Cantilever Tendons - Longitudinal post tensioniog installed in the top slab of segmental bridges built io balanced cantilever. Cast-in-Place Segmental Bridge- A Bridge constructed with cast-in-place segments. Casting Curve - This is the geometric profile to which the segments must be made in order to achieve the required theoretical bridge profile after all final structural and time-dependent (creep and shrinkage) deformations have taken place. Closure - Cast-in-place concrete segment or segments used to complete a span.
Continuity Tendons- Longitudinal post tensioning installed in the bottom slab of segmental bridges built io balanced cantilever. Diabolo - Details for continuous duct placement through deviation saddles, and for connection at diaphragms (Figure 2.3)
Deviation Saddle -Build-out in the web, flange, or web-flange junction to provide for change of direction of an external tendon.
Deviation Trumpet- Detail for tendon connection of deviation saddles and diaphragms to provide tolerance for angle of tendon connection (Figure 2.4). External Tendon - Tendon located outside the flanges or webs of the structural member, generally inside the box girder cell. Erection Truss Span-bv-Span - This is a custom built truss which rests underneath a span on supports connected to the pier and/or previously erected superstructure onto which a complete span of segments is
placed by crane or other device. Such trusses may be self launching to the next span or may be moved by cranes.
Form Traveler - Equipment utilized for construction of Cast-in-Place segmental bridges. Major components include the structural frames (horses), the upper work platform, the lower work platform, and the trailing work platform. The form traveler is used to advance the forms from segment to segment. It also supports the leading edge of the forms throughout the "form-rebar-pour" cycle.
Chapter 2.0- Terminology
Page 3 of 10
Launching Gantry - Custom built erection equipment which is used to take delivery of the segments, lift, move and place them in their fmal erected locations in the superstructure. After completion of a cantilever or span, the gantry is capable of launching itself forward into a position ready to construct the next cantilever, or span. Internal Tendon - Tendon located within the flanges or webs (or both) of the structural member. Long Line Casting - Method of casting segments on a long casting bed which makes up the complete cantilever or span between field closures. Match Cast- Method of casting segments whereby a segment is cast against an existing segment to produce a matching joint. When the segments are separated and re-assembled in the structure, the mating surfaces fit together and reproduce the "as cast geometry." Permanent Post Tensioning- Post tensioning that is required as part of the completed structure. Pier Table- The portion of a cast-in-place segmental bridge that is built atop the piers prior to assembly of the form travelers. In fact, a key factor in the pier table design process is the decision about whether to only provide space for assembly of one form traveler or to provide adequate space for concurrent fabrication of two form travelers. Precast Segments - Box shaped precast concrete elements which can be assembled to form a bridge superstructure or pier (see Figure 2.1). Precast Segmental Bridge - A bridge constructed with precast segments. Common types described in Article 1.3 of Chapter I. Progressive Erection in Cantilever - Segments are erected in cantilever in one direction only from one pier to the next using temporary intermediate piers or temporary cable stays or both to support the advancing cantilever. Segmental Constrnction - the fabrication and erection of a structural element (superstructure and/or substructure) using individual elements, which may be either precast or cast-in-place. The completed structural element acts as a monolithic unit under some or all design loads. Post-tensioning is typically used to connect the individual elements. For superstructures, the individual elements are typically short (with respect to the span length) box-shaped segments with monolithic flanges that comprise the full-width of the structure.
Short Line Casting - Method of casting each segment in a special form called a casting cell using a fixed bulkhead at one end and a previously cast segment at the other as shown in Figures 6.10, 6.11, and 6.12. The form is only one segment long, hence the term "short line. 11
Span-bv-Span Erection - This is an erection method where all the segments for one span are placed on a temporary support truss, aligned, jointed, and longitudinally post-tensioned together in one operation to make a complete span. See Chapter 3.0.
Temporary Post Tensioning- Post tensioning installed solely for erection purposes.
Transverse Tendons- Post tensioning installed in the top deck and perpendicular to the centerline of the bridge, typically to strengthen the cantilevered wings of the segments.
) Chapter 2.0- Terminology
Page 4 of 10
Pier segment /Jiitphl'tiltin
--...
....._......----- ...
-~~-~-~--r~---~
"'"'· Lu»gitudiJl.tJI ~antJJe:w::r
past-le;nsinning T.rans1o>~r.se
Bearing pad pede$lol ro:r
j30$l. · · t~.ti:'Oioning
.neoprt:nc or
1'ypicaJ ~~ecmeni.
pot bearings
,/'/_//
Pier
-tJ(tp
Pie,- !!i:llnfl se-gnu~nt
_/
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pu.-:t ~ten!tiouing
Figure 2.1 -Segmental Bridge Components
Shetu~
key
~"ace ancJUJ-t'
irl recess
Te.rnpur-a;-y
post-'-tensiPning bli-ster
~~~~~~i~~~~~~~~s~;~~~:~~~:::J
l.lppcr P.ernrnncnt posi- ten.-.ionif1C ;;tnchoru,t:fi: Mi.slcr (Duttre!t.s) ror _
r.a,n t.ile- ''i:"-1' pasl-le.nsioiring
Rer::t'!.OJS Qnd duct
ftir lc:mporat'y
pu....·r.-l.cnsionine bnr$
Figure 2.2- Segment Features
) Chapter 2.0- Terminology
Page 5 of!O
n
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concrete around
Use internal
witiJ internal vi bra tors- it csn easily cause voids.
disturb interface
Risk of voids
vibrator to between loads and consolidate
llroroughly. ;:
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• Avoid Jetting t.•ibrator go too deep. (It can cause aer-ation or voiding of earlier placed concrete whic!J has perhaps already started lhe setting process..)
• Also, vibrator con easily get stuck. • Avoid too muclr contact witll duels and rebar.
To consolidate concrete: pus/1 vibrator vertically into concr·ete to depll> of no more t!Jan 2FT (:t) and withdraw slowly, in steps, at l/Je same point. IYUhdraw vibrator from concrete to
move to another poinl~-JlO NOT drag vibrator through concrete. Vibrate at intervals of about IF't. lo
1"-6··.
()
Figure 9.3 7- U•e of Internal Vibrator. for Compaction
Chapter 9. 0- Production ofPrecast Segments
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9.11 Finishing the Top Surface A good quality finish of the top surface is essential as this is also the riding surface. The primary opportunity to achieve this properly is in the casting operation (Figure 9.38). A 1/2-inch sacrificial thickness for grinding or planing is now specified by some states, followed by mechanical grooving of the riding surface. To achieve a good finish by mechanical means, the equipment must be used properly by trained and experienced operators. Care is needed to make sure that all depressions are filled and all high areas removed to give a very uniform, dense and even surface. The surface must be accurate and should be as smooth as possible prior to applying any required riding surface treatment. After such treatment, the surface must still be even and accurate. Undulation should not be permitted. Hand finishing has been used successfully on many segmental structures in the past. Hand finishing requires that a good strong, straight screeding board be used extending from the top of the bulkhead to the top of the match cast segment to strike off the surface to au accurate level. Mechanical screeds also work very well. Good results have been achieved with both rolling and vibratory screeds. Mechanical screeding should be followed by a straight edge, usually a substantial, stiff aluminum beam, worked by hand and used to check and correct any low and high spots to give au accurate and straight surfuce from the bulkhead to the match cast segment. After surface wetness has disappeared, the surface may be very lightly "touched up" with floats to produce a finer and smoother surface. Floats should not be used in such a way as to move concrete or disturb the accuracy of the straight surface.
)
When frnishing a concrete surface, it is important to keep the concrete live for working by proper vibration, tamping and floating, and leave as if not to add water to wet any stiff areas. This will create patches of weaker surface material which will dust and wear badly in use. In order to take advantage of workable concrete, the initial leveling and frnishing should following immediately after placement. This is the best time to get the surface level. The best quality can be achieved by frnishing the segments to a smooth finish, and then providing a transversely grooved riding surface cut after erection of the structure. A small amount of extra cover is specified to allow for the depth removed by the grinding process prior to grooving. Be careful not to spoil the top surface when and if the concrete is to be covered for curing. (Use means to support tarps and prevent contact with top surfaces, etc.) The top surface of the bottom slab should be finished in a similar manner, although the appearance of the surface finish is not so critical, it should, nevertheless, be accurate. Mechanical screeds need not be used on the bottom slab.
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Use a mechanical screed to give accurate level from match cast. segment to bulkhead. Remove high spots, fill in low spots to unif01·m. dense, even surface.
After mechanical screed, use straight edge to check for and remove localized high and low spots fo give an accurate, dense and straight surface from bulkhead to rna lch cast segment. After surface wetness has disappeared, floats may be used very lightly to provide a smoother and liner surface.
4. Wearing surface lreatmenl. suciJ as grooving. is usually
done in IIJe field after erection.
Figure 9.38- Finishing Concrete Suiface
9.12 Curing In order to achieve a production rate of one segment per day from one casting cell, it is essential to ensure that curing is proper and sufficient to provide the necessary strength and control of shrinkage, etc. Project Specifications or Special Provisions prescribe the curing procedures to be followed. Curing procedures depend upon the type of concrete, its chemical hardening processes, temperature and exposure conditions. It is common practice to cover the segment with tarpaulins and apply steam to maintain a controlled temperature and humidity. Other methods have been used, including burlap, blankets, water, etc. With a production rate of one segment per day, clearly the curing process in the casting cell cannot be more than a few hours from the completion of the casting in the evening to the start of survey and stripping the next morning. This is why a controlled environment is essential. The segment curing may be obtained with chemical compounds or water, and should be in accordance with the contract documents.
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9.13 Forms Stripping of forms should not start until the concrete has reached the required strength. This is usually specified at 2500 psi. At this strength, it is normally possible to ease off the side forms, remove the core form, and pull back the match cast segment provided that the top slab is selfsupporting. At this strength, the segment could also be moved on its pallet but not lifted. In case the reinforcing provided is incapable of carrying the weight of the unsupported top slab at 2500 psi, then transverse post-tensioning must be stressed in full or in part. This would require a higher strength often specified at 4000 psi. It is customary to break cylinders in order to verify that these strengths are in fact obtained. Transverse post-tensioning of the top slab in the storage yard is illustrated in Figure 9.39. Stripping the forms should be done with care, as it is very easy to cause spalling and other damage when the concrete is young.
)
Figure 9.39- Transverse Post-Tensioning of the Top Slab in the Storage Yard Most casting cell forms are removable in whole pieces (Figure 9.40), but it is advisable to leave removal of any special block-out forms for as long as possible, as it is very easy to break the edges ofblockouts. Stripping and pulling back the match cast segment should be done with particular care. If the bond breaker has not been properly applied, portions can be broken off either segment. The shear keys are especially vulnerable. Also, the movement mechanism on the pallets must be examined
and understood by the stripping crew. Loosening of jacks and tilting of the pallet can "lift" the newly cast segment (see Figure 9.41). This motion can easily damage the shear keys and must be avoided. Segments may be separated by the following methods:
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• • •
heavy-duty steamboat ratchets hydraulic jacks either mounted on the soffit or manually (see Figure 9.42) hydraulic jacks on the soffit table and on the top deck through lifting blockouts
When concrete reaches required strength commence striking forms I. Disconnect inflated duct liners or mandrels 2. Remove wing bulkheads 3. Drop wing soffit and pull back web outside forms 4. Strike core forms, fold back and retract 5. Strike and pull back match cast segment (Use caution to avoid damage to shear keys, etc.- see Figure 9.41) 6. Pull segment back from bulkhead (Use caution to avoid damage to sbear keys, etc.)
-
1
2
Figure 9.40- Stripping Forms
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Inside formwork ~Bulkhead
New segment
/ / /
This key will not jam Tllis key wi/1 jam&- break
_ _--t;=ya--
CAUTIO!i;. In order to break the bond bet ween the matcb-·casl a.nd bulkhead. it is normal to
-release lhe rearward SC'rews/jack
to a/low segme11t to lilt back. Point of This can ca-use damage to sl1ear ro·talion keys. Grea-t care is needed wit li this operation. ll may be necessary lo try a few techniques depending upon the form m·ec-hanisms. 111er.e is
no simple solution.
) Figure 9.41-Striking Match Cast Segment
)
Figure 9.42- Formwork Device for Separation ofSegments (Photo courtesy of Southern Forms, Inc.)
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9.14 Special Situations- Elevated Light Rail Construction An aerial guideway has all the standard issues of a typical precast segmental project with the added features for light rail operations. These light rail features will require additional review to determine cost impact. Coordination ofLRT systems integration work will require upfront planning and add to the normal QC/QA efforts throughout the project. The precast segments can be much smaller than highway units.
9.14.1 Rail Construction The rails (commonly continuous welded rail) may be directly fixed to the guideway with elastic fasteners or raised above the deck by using concrete plinths. Direct fixation rail
will necessitate tight construction
control. If plinths are shown, the contract documents will specify the design criteria, usually CIP once the structure is erected. Alternates to allow rebar couplers to avoid projected rebar or to allow the plinth construction at the casting yard may be present. The plinth layout will detail intermittent gaps to provide deck drainage. The requirements for concrete surface treatments for secondary plinth pour areas can prove
costly. Also, some upcoming projects are requiring the concrete plinth rebar to be fiberglass. Carefully review project specifications. The locations of specialwork, switchgear, high strength rail, rail expansion joints and rail anchors will require close shop drawing detailing. Address clearance issues with an RFI to avoid casting yard delays.
Identification of the design, location and installation requirements of all LRT features will be crucial. The system integration placement requirements will probably necessitate a fulltime electrician at the casting
yard.
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··~
Figure 9.44- Plinth steel added to the rebar cage
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·..
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Figure 9.45- CJP plinths with final preparation before rail placement
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9.14.2 LRT Electrification
···~
Methods used for traction power system electrification include a third rail or installing a series of overhead catenary lines (OCS) to operate the trains. Either option will add to the standard coordination factors at the casting yard. The industry does utilize AC and DC traction power systems. Most modern light rail projects are using DC traction electrification system (TES), so our focus is DC current.
Figure 9.46- Rebar added for center mount OCS pole
9.14.3 Cross-over Construction An aerial guideway with northbound and southbound tracks will detail a cross-over at certain intervals. The crossover area will be congested with additional rebar and systems integration requirements. ClarifY the tolerance requirements during the early stages of the project to avoid casting delays and QC/QA shortfalls. The segments in these tight construction control areas may not meet the daily casting cycle. A preconstruction meeting with the project LRT consultants is warranted prior to casting these segments.
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Figure 9.47- Crossover rail layout prior to secondary concrete pour
9.14.4 Grounding Requirements
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DC stray current can cause corrosion of the transit system infrastructure grounding safeguards will be built into the structure. The post-tensioning system and concrete reinforcement may have grounding system to
eliminate the cumulative effects of the stray current to increase the longevity of the structure. These measures will also ensure personal safety of the passengers, operators and maintenance crews. Proper
training of production crews and QC/QA staff will ensure competent work procedures are maintained.
•
Post-tensioning
The contract documents may require grounding the post-tensioning system due to stray current migrating to
the PT tendons. Each tendon will normally require grounding only at one post-tensioning anchorage. One method is to prep ao area on the backside of the post-tension anchor and attach the ground wire with an exothermic weld. The individual copper jumper wires can be crimped together and attached to the topslab reinforcement mat.
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•
Topslab Reinforcement The upper layer of reinforcement of the topslab may require grounding. One method requires tackwelds on all or a portion of this reinforcement mat. This will entail the use of ASTM A 706 weldable rebar, which should be specified in the contract documents. A ground wire is then attached with a crimping tool.
•
Miscellaneous Metals Project specifications could require all metallic embeds to be grounded, including patron barriers, hand rails, expansion joints, access hatches, etc. Grounding continuous items like handrails may mitigate the grounding requirement to every 40 feet. These requirements can be project specific. Verify if a copper jumper wire is necessary or addition rebar pieces and tie-wire will suffice. An item checklist with specific requirements and frequency will mitigate cost and inspection needs.
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Figure 9.49- Grounding wire exothermic-welded to access hatch No. 1 in the picture above shows the exothermic connection of the copper grounding wire.
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No.2 is a styrofoam blockout that will enable the ground wires to be connected to the conduit system within the precast structure.
9.14.5 LRT Conclusion Light rail projects add to the complexities of segmental construction, but proper focus on details will prove successful. A methodical approach to the additional aspects oflight rail construction and suitable managerial oversight will mitigate the learning curve. Contractors and precasters should welcome this application of the technology.
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TABLE OF CONTENTS
CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 10.0 PROCEDURES FOR HANDLING TRANSPORTING AND ERECTING PRECAST SEGMENTS 10.0 10.1 10.1.1 10.1.2 10.1.3 10.2 10.2.1 10.2.2
3 3 Lifting Holes Cast in the Top Slab of Segments 3 Inserts Embedded in the Segment Webs and Protruding Above the Top Slab 4 Lifting Slings or C Hook Frame 5 Handling and Transporting of Precast Segments in Precast Yard 6 Handling precast segment from the new-cast position to the match-cast position 6 Procedures for Handling, Transporting and Erecting Precast Segments
Methods of Lifting Precast Segments
Handling and Transporting of Precast Segments From the Casting Area to the Storage Area
)
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 10.3.3 10.4 10.4.1 10.4.2 10.4.2.1 10.4.2.1.1 10.4.2.1.2 10.4.2.1.3 10.4.2.1.4 10.4.2.1.5 10.4.2.1.6 10.4.2.2 10.4.2.2.1 10.4.2.2.2 10.4.2.2.3 10.4.2.2.4 10.4.2.3
Transporting Precast Segments from the Precast Yard to the Erection Site Transporting Precast Segments via Water Using Barges Loading Transport Unloading Transporting Precast Segments Off-site via Land Loading Transport Unloading Transporting Precast Segments On-site via Land Erection of Precast Segmental Bridges Factors for the Selection of Precast Segmental Bridge Erection Methods Erection Methods for Precast Segmental Bridges Erection Methods for Span-by-Span Type Bridges Underslung Trusses with Crane on Ground or Barge Mounted on Water Erection on Underslung Trusses with Crane or Derrick/Lifter on Deck Erection with an Overhead Gantry Full Span Erection with Winches I Strand Jacks Full Span Carrier I Erector Full Span Erection on Shoring Falsework Erection Methods for Balanced Cantilever Bridges Balanced Cantilever Erection by Crane on Ground or on Water Balanced Cantilever Erection by Overhead Gantries Balanced Cantilever Erection with Beam and Winch/Strand Jacks
Balanced Cantilever Erection with Special Erectors Erection Methods Conclusion
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6 11 11 11 12 12 14 14 14 15 15 19 19 21 22 22 24 25 27 28 29 30 30 32 34 36 37
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TABLE OF FIGURES
CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 10.0 PROCEDURES FOR HANDLING TRANSPORTING AND ERECTING PRECAST SEGMENTS
Figure 10.1 Figure 10.2 Figure 10.3 Figure 10.4 Figure 10.5 Figure 10.6 Figure 10.7 Figure 10.8 Figure 10.9 Figure 10.10 Figure 10.11 Figure 10.12 Figure 10.13 Figure 10.14 Figure 10.15 Figure 10.16 Figure 10.17 Figure 10.18 Figure 10.19 Figure 10.20 Figure 10.21 Figure 10.22 Figure 10.23 Figure 10.24 Figure 10.25 Figure 10.26 Figure 10.27 Figure 10.28 Figure 10.29 Figure 10.30 Figure 10.31 Figure 10.32
5 7 Straddle Carrier Transporting Segments to Storage. New Baldwin Bridge. CT 7 Gantry Crane on Rails, Singapore LRT Storing and Stacking of Segments 10 Double Stacking of Segments 10 Barge Transportation of a Segment Hauler 13 13 Barge Transportation of Segment Gantry Loading Segment on Segment Transport Vehicle, New Baldwin Bridge, CT 16 Truck and Segment on Trailer, New Baldwin Bridge, Connecticut 16 Delivery of Segment to Launching Gantry, New Baldwin Bridge, Connecticut 17 Segment Lifted by Launching Gantry, New Baldwin Bridge, Connecticut 17 Delivery of 85 Ton Diaphragm Segment for the Boston Central Artery Project 18 Crane Erection of Span-by-Span Bridges on Underslung Trusses 22 Crane Erection of Span-by-Span Bridge on Underslung Trusses 23 24 Span-by-Span Erection on Underslung Trusses with Crane or Deck Span-by Span Erection with an Overhead Gantry 25 Span-by-Span Overhead Gantry Segment Erection 26 Full Span Overhead Erection with Winches 27 Full Span Erection, James River Bridges, Rl 27 Full Span Carrier I Erector 28 Full Span Erection on Shoring Falsework 29 Full Span Erection on Shoring Falsework 29 Balanced Cantilever Erection by Crane 30 Balanced Cantilever Erection by Crane 31 Balanced Cantilever Erection by Barge Mounted Crane 31 Balanced Cantilever Erection by Overhead Gantry 32 Balanced Cantilever Erection by Overhead Gantry 33 Balanced Cantilever Erection by Overhead Gantry 33 Balanced Cantilever Erection with Beam and Winch 34 Balanced Cantilever Erection with Beam and Winch SFO Skyway Bridge 35 Special Erector Used on the Dallas High Five Project, TX 36 Special Erector Used on the Dallas High Five Project, TX 37 Handling Segments
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10.0 Procedures for Handling, Transporting and Erecting Precast Segments Regardless of the chosen erection method, the segments could be handled and transported multiple times. Typically, the segment will be handled and moved within the casting area, moved to the storage area, and from there the segment will be transported to the bridge site for erection. This chapter describes most of the methods that have been used in handling, transporting and erecting segments.
10.1
Methods of Lifting Precast Segments Precast segments can be lifted using one of the following options:
10.1.1 Lifting Holes Cast in the Top Slab of Segments Depending on the segment weight and design, 4, 8, I 0 or more bars may be needed to lift the segment. Lifting bars are typically high strength bars ranging in diameter from I W' to 3". The lifting bars, couplers and nuts are usually reused. The number of reuses should be per the manufacturer's and/or specialty Engineer's recommendations. The lifting bars, couplers and nuts should never be reused if they have been over stressed, bent or otherwise abused. The high strength lifting bars should never be welded or exposed to arcing. The bars should be removed prior to performing any welding on the lifting frame.
)
Typically lifting holes are positioned through the top slab near the inside or outside of the webs. The holes may be formed using corrugated PT duct pieces, tapered inserts, or other methods may be specified by the Engineer. The exact positioning of these lifting holes is critical. It is important to develop a proper positioning and restraining device that will hold the forms in place during the concreting operations. More than one positioning device might_:!Je needed to accommodate the variations in the lifting hole layout. It is important to develop a quality control procedure to insure that the right layout is used. The bars may be overloaded, the segment may not hang properly or the lifting frame may not fit if these holes are not positioned correctly, or if they move during the concrete pour. The lifting frame is secured to the segment through the formed holes with PT bars (Figure IO.l(a)). The slope and cross fall of the segment can be adjusted by changing the connection points on the lifting frame, by varying the sling length, or by hydraulically adjusting the relative position of the frame and the segment. It is essential the proper stressing requirements of the PT bars is followed when securing the frame
to the segment. The system could be designed to rely on the friction developed between the frame and the segment to insure that the bars are working in tension. If the bars are not stressed properly. the frame could slip and shear the PT bars. After erection of the segments, the lifting holes should to be plugged with an approved non-shrink grout, or as specified by the Engineer. The hole forms used in the casting yard should provide a surface that will insure a proper bond between the plug and the segment, and prevent the plug from falling out.
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Providing access to form, pour, strip and finish the bottom of the holes, especially when they are outside the webs may require the use of rolling platforms, personnel lifts, or other movable platforms. Access inside tall and sloped segments may require the use of sophisticated movable scaffolding to reach the lifting holes locations.
10.1.21nserts Embedded in the Segment Webs and Protruding Above the Top Slab Lifting devices that could be embedded in the web include high strength bars, looped strand bundles, or special inserts. The high strength bar, plate, nut and coupler assemblies are encased in aPT duct. Care must be taken when placing the assemblies to ensure that the bottom nut and upper coupler are fully engaged on the bar.
Because of the lack of visual confirmation, this system poses a risk of accidents if the nuts, couplers and bars are not properly engaged and secured. However, with proper quality control, it has been used successfully on many projects. The lifting bars, couplers and nuts typically cannot be reused because they are embedded in the concrete. High strength lifting bars should never be welded or exposed to arcing. The lifting frame is secured to the embedded PT bars. The slope and cross fall of the segment can be adjusted by changing the connection points on the lifting frame, by varying the sling length, or by hydraulically adjusting the relative position of the frame and the segment. It is essential to follow the proper stressing requirement of the PT bars when securing the frame to
the segment. The system may be designed to rely on the friction developed between the frame and the segment to insure that the bars are working in tension. If the bars are not stressed properly, the frame may slip and shear the PT bars. After the segments are erected, the bars may require trimming to provide adequate concrete cover,
and the PT duct encasing the bars has to be grouted. The bars and couplers should to be protected from damage throughout the project, and could cause tripping hazards when they are protruding above the deck, or recessed in holes. Special precast handling inserts may also be used to lift the segments. When using these inserts it is important to follow the recommendations of the manufacturer.
When looped strand bundles are used to lift the segments, the loop embedment length and details must be properly designed. The top of the loop should be encased in a metallic light weight pipe section and then bent in a U shape. The pipe section is used to make sure that the load is evenly distributed among the strands. The bottom of the loop should be properly secured to the web rebar as detailed on the shop drawings. The strand loops should be properly positioned in the segment and a recess form should be used around each loop penetration. The proper positioning of this recess form may be problematic and hard to maintain during the pour. After erection, the loops are trimmed inside the recess to provide the proper concrete cover. The
recess is then filled with the specified grout or patching material. The recess detail should be analyzed carefully in order to keep the patch from popping out under traffic.
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The exact positioning of any of these inserts is critical. It is important to develop positioning and restraining device that will hold the inserts in place and plumb during the concreting operations. More than one positioning device may be needed to accommodate the variations in the lifting insert layout. A quality control procedure is required to insure that the right layout is used. The inserts may get overloaded, the segment may not hang properly, or the lifting frame may not fit if these inserts are not positioned correctly, or if they move during the concrete pour. The use of embedded rebar to lift the segments is not recommended.
10.1.3 Lifting Slings or C Hook Frame The segments may be lifted without the use oflifting holes or embedded inserts. Lifting slings, flat braided wire rope, or nylon straps (Figure IO.l(b)) may be used to handle the segments.
This method is not suitable for balanced cantilever erection, or in sitmi.tions where the segment must be placed in its final position prior to disconnecting from the erection equipment. Slings are commonly used to lift the segments for precast segmental erection using underslung trusses or falsework. Wood, plastic, or rubber softeners or shoes should be used around the segment edges to prevent any damage to the segment or slings. Another segment handling system that does not require the use oflifting holes or embedded inserts is the C hook lifting frame (Figure IO.l(c)).This lifting frame can get quite heavy when handling large segments and could affect the selection and size of the erection equipment.
)
In some situations, a combination of lifting devices might be used on the same segment. The segment could be lifted with a sling in the casting yard and during transport, and then erected with a lifting frame at the erection site. The segment structural integrity should to be verified regardless of which lifting system is used. At least one lifting option that is acceptable to the designer should be shown on the contract drawings. Tiu:nbuck/es or lor control
~celp$
of crosstaJJ
C-Hook
Fl;:~rt
1./(bJ
Pmtectiw shoes and hlirdwood pScks to a wid damsge tq
Adjusting Jatenrl posiUon_ D! frame will ttl/ow segment to hang at required cross/all with 4 $ingle centrAl lift.
corpers When lifting
with slings,
Shim Profiled shim
tilling with a lt'iJme Is pretered and
is often lhe only solution tor erectioJt.
Figure 10.1-Hand/ingSegments
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10.2 Handling and Transporting Precast Segments in Precast Yard 10.2.1 Handling precast segment from the new-cast position to the match-cast position The first time the new segment is handled is when it is being moved from the new-cast position against the bulkhead to the match-cast position. Typically, the main operations affecting the handling are as follow: 1)
2)
3)
4)
5)
6)
The sides and bottoms of the inner core form are loosened up. The concrete should have attained the minimum strength requirements identified in the casting manual before performing this operation. None of the form elements supporting the concrete should be distrubed. The segment should not be exposed to excessive vibration. Typically no post tensioning is required to perform these operations. It is essential that the as-cast survey of both new cast and match cast segments be performed before starting any loosening or stripping activities on the forms. The match-cast segment is broken free from the new-cast segment. The segments should be separated as indicated in the casting manual and in accordance with the recommendations of the form designer. Typically, the soffit table under the match cast segment is tilted slightly as the tables are pushed apart using horizontal hydraulic or mechanical jacks. It is important to keep in mind that the segment separation takes place while the concrete is still relatively green, and the shear keys are especially vulnerable to breakage. The match-cast segment is rolled away on its soffit. Once the segments are separated, the match cast segment is rolled on its table using a winch, a hydraulic system, or a loader. The inner core form is lowered and retracted and the wing forms are lowered. When the concrete has reached the appropriate strength and, if required, the transverse PT is stressed. The transverse PT may be stressed in stages. The form elements supporting the concrete can be removed, the core form is folded and retracted, and the wing forms are lowered. The new-cast is freed from the bulkhead. Depending of the form design, the new cast segment may be separated from the bulkhead using the same method as for the separation ofthe match cast segment. The segments should be handled carefully in order to avoid shear key breakage. The new cast segment is rolled on the soffit form. Once the new cast segment is separated from the bulkhead, it is rolled on its table using a winch, a hydraulic system or a loader. Later, after the rebar cage installation, the new cast segment is rolled again, and is set and adjusted in the match cast position.
10.2.2 Handling and Transporting of Precast Segments From the Casting Area to the Storage Area Depending on the yard set up, point and patch needs, PT requirements, grouting, transverse PT pour backs, and other finishing issues, the segment will be moved to either an intermediate finishing area or directly to the storage area where it will be finished. Before lifting the segment, the concrete should have reached the specified lifting strength and the required transverse PT should be stressed. Storage areas should be properly prepared to prevent any settlement under the segments. Once the segment is connected to the lifting frame or to the slings, it can be moved to the storage yard.
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Commercially available equipment could be used to move the segments from the casting area to the storage area. However, due to the site conditions, yard layout, optimization of the operations
and economics, custom built equipment may be better suited for the project (see Figure 10.2).
Figure 10.2- Straddle Carrier Transporting Segments to Storage, New Baldwin Bridge, Connecticut (photo courtesy of Perini/Homsi)
J
Figure I 0.3 - Gantry Crane on Rails, Singapore LRT (photo courtesy ofDEAL!Rizzani De Eccher USA)
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The segment lifting frame dimensions and weight should be considered in reference to the capacity of handling equipment. Safety details such as wheels guards equipped with automatic engine kill switches, travel alarms, air horns, proper communication between the operator and the spotters, and other safety devices are essential to the safe operation of the large handling equipment in the narrow runways of the storage area.
Some of the typical methods used to move the segments in the yard are: 1) Cranes with or without tractor/trailers or special carrier Depending on the project needs, the availability of equipments and economics, the segments may be moved using large cranes to either load the segments on tractor/trailers or special carriers, or to crawl with the segment directly into the storage area. This method may be inefficient, but may be used if the storage area layout can accommodate large runways for the travel and swing radii of the cranes and the transporters. 2) Rail Mounted Gantry Cranes (see Figure 10.3) If the yard layout is rectangular and all the segments can be stored on a long and narrow strip of land, a rail mounted gantry crane would be the ideal solution. This type of equipment can operate in very narrow runways and optimizes utilization of the storage area. The rail mounted crane can typically straddle several segments. If electric power is available, this type of gantry could be operated using electric umbilical cords running off the permanent power grid. This solution is usually more economical that equipping the gantries with generators. Rail mounted gantry cranes require special foundations under the rails and should include provision to correct for any ground settlement under the tracks during the life of the project. These gantries require relatively flat terrain. 3) Rubber Tired Straddle Cranes
If the storage area is square or irregular, a rubber tired straddle crane might be needed. These cranes typically straddle one or two segments and will require multiple runways. The runways should be wide enough to allow the safe operation ofthe equipment between the rows of segments.
This equipment is typically capable offour wheel steering and four wheel drive operations. These features are quite helpful when negotiating tight turns in the yard. The tire pressure exerted by the straddle cranes is quite high and requires proper soil preparation. Furthermore, measures should be taken to constantly monitor and dress up the runways. Ignored ruts and depressions will affect the operation of the equipment, and will cause premature wear and tear on the drive and steering mechanisms. Proper drainage throughout the casting yard must be provided to avoid water ponding in the runways. The path and turning radius of straddle cranes must be considered when laying out the casting yard. The straddle crane manufacturer should be made aware of the soil conditions and terrain topography in order to properly size the drive and steering systems.
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The soil conditions in the storage area must be analyzed and proper soil preparation must be provided to minimize any settlement under the weight of the segments. Crane mats or concrete pads may be needed to spread the load. The segments should be stored on hard timber blocks using a three-point support configuration (Figure I 0.4) in order to avoid warping the segment during the storage period. Warping of the segments would cause complications in fit up of the segments during the erection and the fmal geometry of the bridge. Variable depth segments require more complex cribbing due to their sloped bottom soffits, in order to keep the segments vertical and provide proper stability. The storage area should be monitored periodically, especially after heavy rain, to check for any settlement of the segment supports. If a settlement is observed that would jeopardize the stability of the segment, or if the three-point support configuration has been compromised, the segments should be relocated, and the settlement problem should be corrected. Double stacking of the segments is not always permitted, but is possible depending on the design of the segment (See Figure 10.5). It is essential that the designer check the effects oflocalized loadings due to stacking to avoid cracking. Double stacking requires the approval of the Engineer. The segments should be periodically checked for any damage resulting from the double stacking. Barrier rebar projections must be considered when double stacking. Double stacking of severely variable depth segments is not recommended. When double stacking is being considered it is essential to check that the segment handling equipment has the clearance to clear two segments with rebar projections on dunnage, as well as a
segment with a lifting frame and rigging under the hook. Non-synunetrical segments may crack under their own weight, and may require special attention
for storage. Finishing of the segment could be done in the fmishing area or in the storage area. Access should be provided for transverse post-tensioning and grouting, cleaning of the joint faces, point and
patch, secondary pours, and repair of small defects. If secondary pours are needed, it is important to provide runways wide enough to accommodate concrete trucks or other delivery methods.
No repairs should be made on match-cast faces.
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Three point support in storage to prevent warping NOTE: Supports under webs
Figure 10.4- Storing and Stacking ofSegments DOuble_ StnCI{iritJ is Oiiljl .POSSible if allOwed -by spticllkiltions aJli] has
been approved by_ EngJneer
Use 3-point support
Check localized condiUons for structural adequacy
(Engineer)
Periodically monil11r stack~d segments for any evidence of undesirable effects
such 8S cracking stJd lake t;tppropriale action if necessary..
Figure 10.5- Double Stacking ofSegments
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10.3 Transporting Precast Segments from the Precast Yard to the Erection Site Before the segments are transported to the erection site, it is important to verify that all quality control documents are properly completed, and that the segment has been accepted for incorporation in the bridge. As a minimum, the segment should be checked for the following: I) 2) 3) 4) 5)
Proper concrete strength Specified curing duration is met. This duration could vary from 7 days to 6 months. Transverse PT tendons are stressed and grouted per the contract documents. All the patching and repairs are completed and accepted by the quality control inspectors. All permanent and temporary post-tensioning ducts are checked for obstructions, correct layout, and placement.
6) All inserts are checked for correct placement. 7) Proper identification and orientation of the segment. 8) The segment match cast face has been pressure washed or lightly sandblasted. Depending on the site conditions, and the location of the casting yard relative to the erection site, the segments may be transported by water or by land.
10.3.1 Transporting Precast Segments via Water Using Barges When the casting yard location is remote from the project site, or when the bridge is to be erected over water, segment delivery by water should be investigated. This method usually requires double handling of the segments, especially if a portion of the superstructure is over land.
10.3.1.1 Loading If the casting yard does not have access to a navigable waterway, the segments will be transported as described in section 10.3.1.2 to a location with access to a navigable waterway.
If the casting yard has easy access to a navigable waterway, the following items must be considered: I) Any permitting issues that would restrict access to the waterway from that property. 2)
Water depth adjacent to the edge of the project. Dredging permit requirements, and buried utilities in the vicinity of the property shore line.
3)
Abutters issues
4)
Waterway width and the potential for blocking the channel during the loading of segments
5)
If an existing bulkhead is available, it should be checked for structural integrity and fitness. If found deficient, permit requirements to improve the existing bulkhead must be investigated.
6)
Equipment and segments lateral loading of the bulkhead.
7)
New bulkhead design and permitting issues: a. Bulkhead parallel to the shore line: probably easiest to permit, but could block the channel during the loading of the barges. b. Barge loading slip dug out inside the property line. This method could result in a large slip in order to accommodate the barge sizes being used to
transport the segments. c. Loading finger piers protruding in the waterway. Probably the least expensive and most difficult to permit. This method would consist of two rows of piling with runways. Lateral stability and side loading should to be investigated, especially in waterways subject to ice loading.
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If a slip or finger bulkhead type is selected, the barges could be loaded directly with the straddle crane used in the storage yard. If a bulkhead parallel to the waterway is selected, the segments will be delivered to the bulkhead area by the straddle crane and will be loaded on the barge using a crane with enough capacity to reach to the centerline of the barge. This method will require additional sets of segment storage pads and lifting frames at the bulkhead to stage the segments during the transfer from the straddle crane to the loading crane.
10.3.1.2 Transport The barges used for segment transport must be checked by a qualified Engineer or Marine Architect to certifY the integrity and fitness of these barges. Figure 10.6 shows barge transportation of a segment hauler. Another view of segment transport by barge is shown in Figure 10.7. ABS certification may be required. A proper cribbing and tie-down system must be provided to secure the segments during the transport. Variable depth segments require a more complex and adjustable cribbing and tie-down system. The hull of the barge must be checked and strengthened as necessary to accommodate the segment loads. The depth of the waterway, especially outside the navigational charmels, must be checked and cleared of any obstructions. Water depths affected by tides, seasonal variations and prevailing winds, should be evaluated. Freezing rivers and waterways could have a major impact on the segment delivery. The weather forecast should be checked prior to loading and moving the barges. Since barge towing is quite weather dependent, the logistics of transport, on-site mooring and storage should be studied in details. The path of the tugboat and the loaded barges should be checked for overhead obstructions, low clearance bridges, movable bridge schedules and operational reliability, etc ...
10.3.1.3 Unloading When the segments are delivered to the erection site it is necessary to pressure wash the exposed faces, especially the match cast faces and any exposed steel or secondary pour back area in order to wash off the salt spray. If the PT ducts were not properly sealed prior to the trip, they must also be flushed with potable water and dried with oil free compressed air.
If the segments can be delivered within the reach of the erection equipment, they will be unloaded directly from the barge. Depending on the wave action and swells in the area, connecting the lifting frames to the segments could be difficult and might require special attachments to guide, hold and secure the frame to the segment as the lifting bars are being tightened and stressed. Pinch point type injuries and falls are a serious concern during this operation.
Due to the potential of bouncing of the frame on the segment as it is being secured, the proper aligmnent of the winch cables inside the block sheaves should verified prior to lifting the segment off the barge. Proper access and fall protection should provide safe access to reach the top slab inside the box, the top of the segments, and the areas to be pressure washed. If the segments are being stored on barges near the erection site, proper mooring must be provided. Mooring should be properly permitted and designed to withstand the local wind, water flow, waves, and swell conditions.
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Figure 10.6 Barge Transportation of a Segment Hauler
Figure 10.7 Bmxe Transportation of Segments
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In some instances the large barges needed to transport the segments to the project vicinity are too large and deep to get all the way to the erection site. In these situations, the segments could be transferred, at a great expense, to smaller barges or could be unloaded and transferred to a land hauler at a potentially equal or greater expense.
If the segments have to be transferred from the barges to land hauler in order to reach the erection equipment, an unloading/staging area near site must be set up. This area will be set up with either a bulkhead parallel to the shoreline a slip or fmger piers as discussed in theloading section above. Water depth and dredging permits should to be investigated. The bulkhead parallel to the shoreline is the most likely solution at the job site. If a bulkhead is used, the segments will be unloaded with a crane and loaded on a tractor /trailer set up or a special hauler and transported to the erection equipment. The haul road should be designed to accommodate the segment hauler's horse power and turning radiuses. A low profile/rough terrain rubber tire straddle crane can be used to move the segments from the unloading area to the staging area, and later on to the erection equipment.
10.3.2 Transporting Precast Segments Off-site via Land When the casting yard is not at the bridge location, the segments could be transported on land by either tractor/trailer or by special haulers. Figures 10.8 through I 0.11 illustrate movement of segments from the storage yard to the erection gantry for the New Baldwin Bridge in Connecticut. Figure 10.12 shows delivery of an 85 ton diaphragm segment to the Boston Central Artery project.
10.3.2.1 Loading The segments could be loaded on the hauler with the same straddle crane used in the storage yard. Typically a section of the storage yard is designated as the loading area. This section should have easy truck access and gantry crane rail crossing.
10.3.2.2 Transport Several issues should be considered when analyzing the segment transport to the erection site: i) The weight and dimensions of the segments often exceeds the legal load allowed on the local streets and highways. ii) The over-weight or over-dimension permitting procedures vary from one locality to another. iii) The existing bridges in the immediate vicinity of the project, and sometimes the only access to the erection site might be derated and load restricted. iv) The haul route might be crossing overpasses, buried utilities, underground box culverts, etc ... all of which might have different load rating. v)
In some regions, no over-weight permits are issued in the spring due to ground thawing
concerns. No segments, heavy loads or equipment can be moved outside the project limits during this period. vi) Police and special escort vehicle might be required. vii) Some locality with traffic congestion concerns or sensitive abutters may impose additional
restriction on the hauling time. viii) Overhead clearances such as underpasses, power lines, traffic lights, overhead utility lines,
etc ... along the haul route should be checked. The barrier rebar on top of the segments is usually the controlling element. ix) The distance from the casting yard to the erection site and the availability of haulers could require the setting up of a staging area at the erection site.
Depending on the segment load and the permit requirements, multi-axle tractor trailer combination might be used to haul the segments. For extra heavy segments, special selfleveling, all-wheel steering hydraulic haulers can be used. Special tractors, weighted down with massive counterweights for extra traction, are
typically used to pull the special haulers. Some of these special haulers are self propelled, however, they move at very slow speeds and could be restricted from travelling over highways. Under certain conditions and if rail sighting are available at both the casting yard and at the erection site, transporting the segments by rail might be a feasible solution. However, the unreliability of the rail system schedule and the lack of control over the railroad operations make this solution a very risky choice.
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)
10.3.2.3 Unloading Whenever possible the segments should be delivered directly to the erection equipment. In some instances, double handling the segments and storing them onsite cannot be avoided. If staging areas are used, and if a crane is used to unload the segments, the crane and haulers will be needed again later on to load and transport the segments to the erection equipment. Alternatively, the haulers can be uuloaded with a low profile rough terrain straddle crane that will later on deliver the segments to the erection equipment. If the segments are being delivered on top of the completed spans, the superstructure should be check for the loaded hauler or straddle crane reactions. The haul roads should be designed to accommodate the segment hauler's horse power and turning radiuses. If the segments have to be transferred to a barge, the sarue set up discussed in "transport off site over water" should be considered.
10.3.3 Transporting Precast Segments On-site via Land In addition to the methods available for off site transport, when the casting yard is located iu the close viciuity of the erection site, the segments can be transported to the erection equipment directly by low profile haulers or special mega haulers. Loading, transporting and unloading: when the castiug yard is on site, the sarue equipment could pick up the segment from the storage area, transport it along the bridge alignment and unloaded it at the erection equipment without the assistance of other cranes or equipment. If a low profile rough terrain rubber tire straddle crane is used it should be designed to be able to pick up the segment from the storage area, travel with the segment along the haul roads and over the completed spans and fit under the tail of the overhead gantry to unload the segment. Typically the straddle wheel gage is designed to match the segment web spacing. Alternately the segments could be delivered on the ground under the gantry or withiu reach of the crane or the winch and beam system. If the full span method is used for the casting of the superstructure (entire span is cast in one element), some customized handliug and transportation equipment is necessary. This method of construction is generally used for very long bridges such as high speed rail projects, and major viaducts or bay crossings.
)
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Figure 10.8- Gant1y Loading Segment on Segment Transport Vehicle, New Baldwin Bridge, Connecticut (photo courtesy ofPerini/Homsi)
)
Figure 10.9- Truck and Segment on Trailer, New Baldwin Bridge, Connecticut (photo courtesy of Perini!Homsi)
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Figure 10.10- Delivery of Segment to Launching Gantry, New Baldwin Bridge, Connecticut (photo courtesy of Perini/Homsi)
)
Figure 10.11- Segment Lifted by Launching Gantry, New Baldwin Bridge, Connecticut (photo courtesy of Perini/Homsi)
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Figure 10.12- Delivery of 85 Ton Diaphragm Segment for the Boston Central Artery Project (Photo courtesy of Unistress Corporation)
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10.4 Erection of Precast Segmental Bridges 10.4.1 Factors for the Selection of Precast Segmental Bridge Erection Methods The main factors that influence the selection of erection methods and equipment discussed below are:
Project schedule and construction duration Superstructure design Access and site conditions Project team Equipment availability
Project Schedule and Construction Duration The project completion date is typically specified in the contract documents. In some instances meeting these completion dates would require accelerated schedules. Accelerated schedules typically require working on multiple fronts and would dictate acquiring specialized and expensive equipment to meet the project milestones. The additional expense associated with the specialized equipment and the acceleration costs can often be justified when the owner offers early completion incentives. On certain projects the construction sequence and traffic phasing might require multiple headings to keep up with the project completion schedule.
.)
Superstructure Design The geometric characteristics of the superstructure including span length, pier height, horizontal curvature, maximum grades and cross slope, and the degree of consistency and repeatability of these characteristics throughout the project have a major impact on the erection methods used. Projects with small segments or very tight radius curves require the use of cranes while large projects with repetitive span layout would favor undersluog trusses or overhead gantries. Short projects with very high piers and heavy segments might require a beam and winch set up to erect the heavy segments. It is important to verify that the superstructure is capable of carrying the additional construction loads introduced by the erection equipments. Ground or barge mounted cranes introduce minimal construction
load into the structure while overhead gantries tends to introduce some of the most significant loads the bridge will ever see during the construction stages. Access and Site Conditions Access and site conditions are probably the most significant factors in determining the most efficient erection method. When working over land, the factors that should be considered range from environmental issues such as wetlands and protected habitats to interferences with local traffic, businesses and railroad crossings. When working over water, the factors that affect the selection process include: Water conditions (depth, flow, ice, etc.) Required permits The feasibility and cost of constructing access trestles Wave action and barge bounce must be taken in consideration when connecting the lifting beams to the segments Salt water splash on the match cast faces and inside the PT ducts must be addressed. Proper design, analysis and certification of transport barges must be performed Loading and unloading facilities must be studied and permitted.
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The availability of suitable real estate in the vicinity of the project site for a casting yard will influence the erection and segment delivery methods. The distance from the precast yard to the bridge site will determine the number of transport vehicles, the need to provide staging areas and double handling or barge docking facilities at the erection site. In case the of a limited storage area where double stacking is being considered, the segments must be checked for that loading condition, and proper dwmage and soil preparation must be performed in order to avoid differential settlement. The route from the precast yard location to the erection site will dictate the size and type of segment that can be transported, especially if the route includes low overhead clearance or weight restrictions. Local ordinances and permit requirements and costs also must be considered when selecting the casting yard location.
The transport route from the casting yard to the erection site must be checked for overhead clearances (power lines and overpasses) and for underground structures (utilities and culverts, etc.). Transport permit requirements vary widely from one location to another and seasonal restrictions may apply. Project Team The experience of the project team, which includes the Owner, Designer, CEI, Contractor's engineer and the Contractor is another major factor that may affect the selection of the erection method. The more experienced the team, especially the Contractor, the more open he will be to considering a sophisticated
erection method if it is deemed to be the most efficient way to construct the project. The availability of skilled labor in the project market is another factor that should be considered during the selection of complex erection methods.
Equipment Availability The availability of erection equipment (cranes or specialized equipment), new or used, the competition among the suppliers and the availability of steel fabricators during the selection process will affect the cost and delivery schedule of the erection equipment, and will influence the selection process. The additional costs associated with the mobilization, assembly and commissioning of new specialized
equipment, and the cost of refurbishing and modifying existing equipment, should not be underestimated as
it is a major component of the cost and time analysis in the selection process. The more expensive specialized equipment will benefit from the economy of scale of larger projects where . the initial investment can be depreciated over a large project.
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-)
10.4.2 Erection Methods for Precast Segmental Bridges The erection methods used for the construction of Precast Segmental bridges discussed in this section are classified according to bridge type as follows:
)
10.4.2.1
Erection Methods for Span-by-Span Type Bridges
10.4.2.1.1
Underslung Trusses with Crane on Ground or Barge Mounted on Water
10.4.2.1.2
Erection on Underslung Trusses with Crane or Derrick/Lifter on Deck
10.4.2.1.3
Erection with an Overhead Gantry
10.4.2.1.4
Full Span Erection with Winches I Strand Jacks
10.4.2.1.5
Full Span Carrier I Erector
10.4.2.1.6
Full Span Erection on Shoring Falsework
10.4.2.2
Erection Methods for Balanced Cantilever Bridges
10.4.2.2.1
Balanced Cantilever Erection by Crane on Ground or on Water
10.4.2.2.2
Balanced Cantilever Erection by Overhead Gantries
10.4.2.2.3
Balanced Cantilever Erection with Beam and Winch/Strand Jacks
10.4.2.2.4
Balanced Cantilever Erection with Special Erectors
10.4.2.3
Erection Methods Conclusion
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1 0.4.2.1 Erection Methods for Span-by-Span Type Bridges 10.4.2.1.1 Underslung Trusses with Crane on Ground or Barge Mounted on Water (Figures 10.13 and 10.14)
Figure 10.13- Crane Erection ofSpan-by-Span Bridges on Underslung Trusses (drawing courtesy ofFlatiron Constructors, Inc.) This is a relatively economical solution if ample room when access is available at ground level.
Access along the bridge alignment must be maintained for the following operations: Foundations and substructure construction Pier bracket installation and relocation Segment delivery Erection crane access and swing radius
Material delivery Support operations Access must be maintained throughout the erection phase. This could be quite costly if working over the water mainly due to trestle and /or barges and tugboat costs. This method is quite dependent on the weather conditions especially when working on the water.
This method is governed by the maintenance of traffic rules when working on land. If working over water, special loading and unloading facilities must be provided. •
The pier brackets supporting the trusses are typically cycled and erected on the leading pier by the erection crane.
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I
Figure 10.14 '-Crane Erection ofSpan-by-Span Bridge on Underslung Trusses (photo courtesy of Flatiron Constructors, Inc.) The relocation of the underslung truss can be accomplished by one of the following methods:
I
Winches and selflaunching oflong trusses: In this method, the long trusses are designed to be self contained and are capable of self launching from pier to pier using winches mounted on the deck or on the trusses. Jacks and grips to push long trusses forward: In this method, the long trusses are designed to be self contained aod are capable of self launching from pier to pier using a hydraulic jacking mechanism mounted to the superstructure and a perforated rail attached to the trusses.
Crane and C hook to relocate short trusses: In this method, the short trusses are fitted with a C hook allowing the trusses to be relocated by cranes from span to span. Crane dragging trusses on pier brackets rollers or on C hook trailers: In this method, long trusses can be relocated from pier to pier using a ground based crane that will partially support the nose end of the trusses while the tail of the trusses are rolling on the pier brackets. The trusses are pulled forward toward the next pier. For short trusses the trusses can be fitted with a C hook attached to trailers on top of the deck. The trusses can be relocated from pier to pier using a ground based crane that will partially support the nose end of the trusses and pull it forward toward the next pier while the rear of the trusses are supported by the C hook on Trailers. This method should be avoided although it is sometimes shown in the contract drawings. Dragging the trusses with cranes is a very
delicate aod risky operation because of the high potential of side loading the crane boom. Combinations of the above The precast yard location and distance from the bridge site has a major impact on the erection operations. If the continuous delivery of segments using a reasonable number of trucks cannot be maintained, the segments will have to be delivered to the site off shift and stored near the erection
site. This operation will result in added cost due to the double handling.
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10.4.2.1.2 Erection on Underslung Trusses with Crane or Derrick/Lifter on Deck (Figure 10.15)
Figure 10.15- Span-by-Span Erection on Underslung Trusses with Crane or Derrick/Lifter on Deck (drawing courtesy ofFlatiron Constructors, Inc.)
)
Access the pier locations must be provided for the following operations: Foundations and substructure construction Pier bracket installation and relocation Access must be maintained throughout the erection phase.
Segment delivery by special carriers or trucks Need to check that the deck can handle the construction loads from the crane and the segment deliveries. Trusses can be relocated using the same methods described above. The Precast yard location and distance from the bridge site has a major impact on the erection
operations. The bridge length and the distance that the segment haulers have to back up on the bridge deck also impact the erection operations. Self-launching of the pier brackets is difficult with underslung trusses so it is likely that separate ground or water based equipment will be required to install and remove the brackets.
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10.4.2.1.3 Span-by Span Erection with an Overhead Gantry (Figures 10.16 and 10.17)
Figure 10.16- Span-by Span Erection with an Overhead Gantry (drawing courtesy of Flatiron Constructors, Inc.) Access to the pier locations must be provided for the foundations and substructure construction.
Depending on the Over Head Gantry (OHG) design, all major segment erection operations could be performed from the OHG and/or the constructed deck. Typically OHGs are more complicated and more expensive than underslung trusses. The segments can be delivered from ground/water level or from behind OHG on the newly erected structure.
In order to speed up the erection operations the segments could be stored under the OHG on the bridge alignment. Span-by-Span erection using and OHG method is typically an efficient solution for light rail applications where the total span weights are relatively low, but it has also been used successfully on highway bridges. Some OHGs are hinged to accommodate tighter radii. The use of an OHG typically provides a greater clearance envelop under the structure Must check for overhead clearances: overpasses, power lines, etc.
This method is also a good solution for the erection of short spans and abutment spans if the OHG is already on site to erect the balance cantilever spans.
During the relocation from pier to pier, OHGs are typically self contained and are self launching. In special situations, the OHG may need the assistance of a crane to relocate some of its supports.
·...
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Figure 10.17 Span-by-Span Overhead Gantry Segment Erection (photo courtesy ofFlatiron Constructors, 1nc.)
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··~
10.4.2.1.4 Full Span Erection with Winches I Strand Jacks (Figures 10.18 and 10.19)
Figure 10.18Full Span Overhead Erection with Winches (photo courtesy ofFlatiron Constructors, Inc.)
Access along the bridge alignment must be maintained for the following operations: Foundations and substructure construction Casting or assembly of superstructure Winch assembly, installation and relocation Segment or concrete delivery Construction equipment access
Material delivery Support operations
)
Access must be maintained throughout the superstructure construction phase. This is not a very common construction method.
The superstructure could be PC segments, assembled on the ground under their final position or CIP full span, either cast on the ground under their final position or delivered on barges. This method also requires additional temporary bottom slab PT to carry the span self weight during the lifting
Figure 10.19- Full Span Erection James River Bridges, RI
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10.4.2.1.5 Full Span Carrier I Erector (Figure 10.20)
Figure I 0.20 - Full Span Carrier I Erector (photo courtesy ofDEAL/Rizzani De Becher USA)
)
Access to the pier locations must be provided for the foundations and substructure construction. This type of erection equipment is typically used on light rail projects where the span weights are relatively low. However it has also been used on larger structures. The initial investment in equipment for this method is quite significant. To be economically feasible, this method must be used on very large and repetitive projects where the cost of the equipment can be depreciated over many spans.
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10.4.2.1.6 Full Span Erection on Shoring Falsework (Figures 10.21 and 10.22)
Figure I0.2I- Full Span Erection on Shoring Falsework (drawing courtesy of Flatiron Constructors, Inc.)
Figure I 0.22- Full Span Erection on Shoring Falsework (photo courtesy ofFlatiron Constructors, Inc.)
)
Access along the bridge alignment must be maintained for the following operations: Foundations and substructure construction Shoring assembly and relocation Segment delivery Erection crane access and swing radius Material delivery Support operations This method can accommodate very tight radii The use of commercially available scaffolding and cranes minimizes the investment in specialized
equipment; making this method very competitive for small projects It is quite labor intensive: ground preparation, tower bases construction, towers erection, towers
adjustment, towers bracing, header beams installation, jacks installation, dismantling the system after erection and relocation to the next span. This method is also slow relative to SBS erection with either overhead or underslung trusses if only one span offalsework is used. To match the speed of a gantry or truss at least two sets of falsework will be required.
·· ...
)
This system is feasible where the maintenance of traffic is not an issue. A more complex falsework system will be required to erect over traffic or railroads.
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10.4.2.2
Erection Methods for Balanced Cantilever Bridges
10.4.2.2.1 Balanced Cantilever Erection by Crane on Ground or on Water (Figures 10.23, 10.24 and 10.25)
Figure 10.23 Balanced Cantilever Erection by Crane (drawing courtesy ofFlatiron Constructors, Inc.)
Access along the bridge aligoment must be maintained for the following operations: Foundations and substructure construction Pier bracket installation and relocation (if needed) Segment delivery Erection crane access and swing radius
Material delivery Support operations Access must be maintained throughout the erection phase. This could be quite costly if working over the water mainly due to trestle and /or barges and tugboat costs. This method is quite dependent on the weather conditions especially when working on the water. This method is governed by the maintenance of traffic rules and ground access conditions when working on land. If working over water, special loading and unloading facilities must be provided. Personnel, material delivery and post- tensioning operations are less efficient when working over water
The use of readily available cranes eliminates the investment in specialized equipment making this method the most economical solution for balanced cantilever erection where easy ground access is
available. This method imposes the lightest construction loads on the superstructure. It can accommodate tight radii and steep grades.
The cranes should be sized to erect the pier segments (typically the heaviest) and all other segments.
Typically the crane works from the end of the cantilever. Special attention should be paid to the midspan segments where the crane could get boom bound while erecting from the side of the bridge. By using ground based cranes, the erection can proceed from pier to pier without having to wait for the closure pour and continuity post-tensioning activities. With multiple cranes the erection could proceed simultaneously on several headings.
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Unlike the specialized erection gantries and trusses, the same cranes can be used to support various activities throughout the project. Furthermore, after the completion of the project these cranes can be readily used on other projects.
Figure 10.24- Balanced Cantilever Erection by Crane (photo courtesy of Flatiron Constructors, Inc.)
Figure 10.25- Balanced Cantilever Erection by Barge Mounted Crane (photo courtesy of Flatiron Constructors, Inc.)
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10.4.2.2.2
Balanced Cantilever Erection by Overhead Gantries (Figures 10.26, 10.27 and 10.28)
Figure 10.26- Balanced Cantilever Erection by Overhead Gantry (drawing courtesy of Flatiron Constructors, Inc.) Access to the pier locations must be provided for the foundations and substructure construction.
Depending on the Over Head Gantry (OHG) design, all major segment erection operations could be performed from the OHG and/or the constructed deck. These would include: Personnel access to work area Pier brackets erection Pier segment erection Installation of post-tensioning platforms Overhead service cranes Material deliveries Pier access Closure pour forming, pouring, and stripping support Integral fmishing bridges A cost-benefit analysis is needed to determine what options make economic sense. It is a very cost effective method if:
The bridge is long with repetitive spans. Restricted access at ground level Existing gantries are available and require a minimum of modifications. The possibility of reuse of the gantries is much greater if they are properly designed with versatility for future projects in mind. The project alignment including assembly area must be checked for overhead obstructions such as power lines and overpasses. OHG tend to be manufactured overseas. Adequate time should be anticipated for shipping, custom clearances and trucking to the project site. Due to the long lead time on certain components, the major spare parts should be ordered in advance and available on short notice.
Local electricians, hydraulic mechanics and suppliers of metric odds and ends should be identified early on and should be involved in the commissioning of the equipment.
Chapter 10.0 Procedures for Handling, Transporting and Erecting Segments
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)
Assembly and commissioning of the custom made OHGs typically takes much longer and costs more than anticipated. Due to the project layout and the construction sequences, the OHGs may have to be relocated from one aligmnent to another. This relocation often can be accomplished using one of the following methods: Dismantling, trucking, reassembling and re-commissioning
Self launching back and repositioning in the new aligmnent Reconfiguring for reverse operations and re-commissioning
Loading complete OHG on special transporters moving it
) Figure 10.27- Balanced Cantilever Erection by Overhead Gantry (photo courtesy ofPerini/Homsi)
Figure 10.28 -Balanced Cantilever Erection by Overhead Gantry (photo courtesy of Flatiron Constructors, Inc.)
Chapter 10.0 Procedures for Handling, Transporting and Erecting Segments
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10.4.2.2.3
Balanced Cantilever Erection with Beam and Winch/Strand Jacks (Figures 10.29 and 10.30)
Figure 10.29- Balanced Cantilever Erection with Beam and Winch (drawing courtesy of Flatiron Constructors, Inc./Kiewit) Access along the bridge alignment must be maintained for the following operations: Foundations and substructure construction Segment delivery Material delivery Support operations Access must be maintained throughout the erection phase. Each segment must be delivered right under its final position. This could be quite costly if some of the segments are over shallow water or land obstructions. For spans over water this method is quite dependent on the weather and water conditions Special loading and unloading facilities must be provided to transfer the segment on barges and vtce versa. Personnel, material delivery and post- tensioning operations are less efficient than when working with an overhead gantry. By using a winch and beam, the erection can proceed from pier to pier without having to wait for the closure pour and continuity post-tensioning. By increasing the number of winch and beam setups the erection could proceed simultaneously on several headings. A large crane is needed to relocate the winch and beam from pier to pier. A typical assembly could weigh as much as segment.
Chapter 10.0 Procedures for Handling, Transporting and Erecting Segments
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(J
This method can lift very heavy segments very high and can be more economical than an equivalent crane or OHG. A separate operation is needed to either erect precast pier segments or falsework for a cast-in-
place the pier table. The superstructure must be checked for the erection loads caused by the equipment. The equipment design and fabrication lead times and the commissioning duration should be considered carefully when scheduling the project.
)
Figure 10.30-Balanced Cantilever Erection with Beam and Winch San Francisco-Oakland Skyway Bridge (photo courtesy of Kiewit/Flatiron/Manson Joint Venture)
Chapter 10.0 Procedures for Handling, Transporting and Erecting Segments
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10.4.2.2.4 Balanced Cantilever Erection with Special Erectors {Figures 10.31 and 10.32)
) !
On certain projects, the typical erection methods discussed above are not well suited for the site conditions. In these situations, special equipment must be developed designed and fabricated. As with any other erection equipment proper review for conformance with the applicable US codes, by a qualified designer, is a necessity. Furthermore these special erection methods tend to be prototypes and as such longer fabrication, commissioning and debugging times should be anticipated.
)
Figure 10.31 -Special Erector (drawing courtesy of Flatiron Constructors, Inc.)
l) Chapter I 0.0 Procedures for Handling, Transporting and Erecting Segments
36 of37
Figure 10.32- Special Erector Used on the Dallas High Five Project, TX (photo courtesy ofDEAL/Rizzani De Becher USA) Safety Using Special Erection Equipment Requires: Properly trained labor force Checklists and procedures Experienced site supervision and construction staff
Experienced construction engineer Inspectors are a 2nd set of eyes Repetitive nature of work causes slacking off which increases the risk of an accident through carelessness.
10.4.2.3 Erection Methods Conclusion Many erection methods available Conditions that might dictate or eliminate certain methods: Design Site conditions Schedule Construction sequence Equipment availability Contractor experience Design to US standard and in conformance with OSHA
·..... )
Design-Build projects and Design-Bid-Build projects, that allow redesign or Value engineering to suit the contractor needs and expertise, lead to optimization, creativity and more competitive bidding.
Chapter 10.0 Procedures for Handling, Transporting and Erecting Segments
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TABLE OF CONTENTS
)
CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 11.0 ERECTION DETAILS
)
··. ·-
11.0
Erection Details
3
11.1
Permanent Post-Tensioning
3
11.1.1 Anderson Technology Corporation - Transparent Sheathing
4
11.1.1 Anderson Technology Corporation - Super Corrosion Protective (Supra Strand)
5
11.1.2 AVAR Post-Tensioning Systems for Segmental Bridge Construction Single Plane/Multi Plane
6
11.1.2 AVAR Post-Tensioning Systems for Segmental Bridge Construction Single Plane/Flat Anchorage
7
11.1.3 DYWIDAG-Systems International- DYWIDAG Post-Tensioning Systems for Segmental Construction
8
11.1.3 DYWIDAG-Systems International- DYWIDAG Post-Tensioning Systems for Segmental and CIP Construction
9
11.1.4 Freyssinet Post-Tensioning Systems- Freyssinet Post-Tensioning Hardware for Segmental Bridges/G-Range Post-Tensioning Systems
10
11.1.4 Freyssinet Post-Tensioning Systems- Freyssinet F-Range PostTensioning Systems
11
11.1.5 Mexpressa- Jacks and Pumping Units
12
11.1.5 Mexpressa - Anchorages and Couplers
13
11.1.6 SDI Post-Tensioning Systems and Services
14
11.1.6 SDI Type C Multistrand Anchorageffype C4.6 Multistrand Anchorage/ Type D Multistrand Anchorage
15
11.1.7 VSL Segmental Bridge Post-Tensioning Systems- Anchorage VSL Type ECiffype ESffype E/PT-Pius Duct System
16
11.1.7 VSL Segmental Bridge Post-Tensioning Systems- Anchorage VSL Type SANS LAB+® System
17
11.1.8 Williams Form Engineering Corporation -The Williams System
18
11.1.8 Williams Form Engineering Corporation -150 KSI All-Thread Bar
19
11.2
Temporary Post-Tensioning
20
11.3
Post-Tensioning Safety Issues
23
11.4
Lifting Segments for Erection
30
11.5
Temporary Supports
31
11.6
Midspan Closure
32
11.7
Construction Schedule and Sequence
33
) Chapter 11.0- Erection Details
I of34
TABLE OF FIGURES CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-5UPPORTED BRIDGES CHAPTER 11.0 ERECTION DETAILS
Figure 11.1
Use of Temporary Post-Tensioning for Erection
21
Figure 11.2
Use of Continuously Coupled Post-Tensioning Bars
21
Figure 11.3
Coupled Post-Tensioning Bars (Continued)
22
Figure 11.4
Anchor Head Hole Pattern
25
Figure 11.5
Jack Alignment with Tendon
26
Figure 11.6
Support of Stressing Ram
27
Figure 11.7
Stressing Personnel Located Away from the Stressing Ram
28
Figure 11.8
Stressing Personnel Safety Harness
28
Figure 11.9
Coupling of High-strength Bars
29
Figure 11.10
Erection Systems: Setting of a Pier Segment and Start of Cantilever
31
Figure 11.11
Erection Systems: Means of Stabilizing Cantilever
32
Figure 11.12
Aligning Cantilevers for Midspan Closure
33
Figure 11.13
Effect of Construction Sequence
34
Chapter 11.0 - Erection Details
2 of34
11.0 Erection Details 11.1
Permanent Post-Tensioning Permanent post-tensioning tendons are installed and stressed as erection of segments proceeds. Both internal and external tendons are used. Internal tendons are located in ducts inside the concrete slabs and webs. They are conunonly used in case of balanced cantilever erection. External tendons are located in polyethylene sheathing which is placed in the interior space of the box girder. External tendons are attached to the structure at the pier diaphragms and at deviation blocks. Comprehensive information on post-tensioning technology is presented in Chapter 3 ~ "PostTensioning Duct and Tendon Installation" of the FHWA "Post-Tensioning Tendon Installation and Grouting Manual" presented in Section II of this Handbook. As an addendum to Section II of the Handbook, information on safety during stressing operations, alternative procedures for calibration of jacks and gauges, and temporary tendon corrosion protection is presented below, and in Section 11.3. Safety PoSt-tensioning stressing operations create very high forces in the tendons and surrounding concrete. Therefore, precautions must be taken to prevent personal injury or damage to the structure. Prior to starting stressing operations, inspect anchorages and surrounding concrete.
Clear the work area of debris to allow for unobstructed movement of the stressing crew. Read and understand all operating and safety instructions for the stressing equipment before stressing tendons. Make sure that all safety stickers applied to the equipment are intact, legible and understood by the stressing crew. Comprehensive discussion of safety issues related to stressing of post-tensioning tendons is presented in Section 11.3. Calibration The FHWA Post-Tensioning Tendon Installation and Grouting Manual requires that all calibrations be performed with specific service gauges and a master gauge as a system. Gauges are often damaged on the job sites as a result of impact or shock, and often two service gauges do
not last the normal six-month period between recalibrations. Recalibration of jacking systems is time consuming and expensive, but can be avoided if the service and master gauges are calibrated
at a dead weight indicator to read true pressure. The dead weight indicator must be calibrated and traceable through the National Bureau of Standards. The contractor should seek approval from the engineer prior to beginning stressing operations to use dead weight-indicated gauges in order to
replace damaged gauges without having to recalibrate the ram and gauges as a system. Temporary Tendon Corrosion Protection Temporary corrosion protection is required for tendons that must be left ungrouted for extended periods due to cold weather or other circumstances. Vapor Phase Inhibitor Powder (VPI Powder) was used for this purpose for many years, but use of this product was abandoned due to health hazard concerns. Currently, corrosion inhibiting oils are being used for temporary corrosion
protection which have detrimental effects on bond. Recently, VpCI Powder has been developed which is non-toxic and biodegradeable. Use ofVpCI Powder is reconunended in preference to corrosion inhibiting oils. Product and material safety data on VpCI Powder may be obtained from: Cortec Corporation, 4119 White Bear Parkway, St. Paul, MN 55110 Toll Free (800) 4-CORTEC, Phone (651) 429-1100, Fax (651) 429-I I22 Email:
[email protected], Internet http://www.CortecVpCI.com
)
Details on post-tensioning systems available for use in segmental bridge construction in the United States are presented in Sections 11.1.1 through I 1.1. 8.
Chapter 11.0 ~Erection Details
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11.1.1 Anderson Technology Corporation
SUPPl..ll=ROF AN[)ERSQf\1 POST-'TEN$10NING SY$TEM Anderson 1"Eictlnology Com()ra~i. . -. -. . ott (AT iri.North .Anl!!i:iCa. 'Ilie Andemon PrlS!'tTensil>riing.Systeni (APS)has evolved win the otijlinal Amei:iC311 syswmto in.clpdeay~ ofi1Tmat¢o:i"':andm¢thadodeveloped ato~nd.theP;>eific Rlm.
~Transparent· sheathing for.ciHi:niai tendons inside box jtir in Tablet.
Jriint
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Fig.-1. Dauble Cased Anchorfi>r Clear Duel Tendon
Table. I.
No. ofOB'Strands.
Dianleter
TranspPnmt Sheathing (mm) UnitMass(kg/m)
O.D.
I.D.
12
88.3
79.9
l.lJO
19
l!O;S
100.7
1.45
21
1362
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Head· Office : Onarimon Ynsen Bldg. 2F
3·23-5 Nishi-Shinbashi Minato-kuTokyo, I 05-0003 JAPAN Phone: +81·3·3437-1999
Fax: +81·3-3437-9581
Unit.Length.
9m (Straight)
USA Office: Old Brolin Place Anderson Island, WA98303 Phone: 253·606-6097 Fa.x : 253·884-5683
:.) Chapter 11.0- Erection Details
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... ··~
Anderson Technology Corporation (Continued)
11.1.1
Fig-2 .~bows on~ Qf .b)jdges !!Ddet s~eptal. CQDSlrUction .!n J~pan'.USliig 100% exte1!1altend\»ls 1o1>e l'rt>tedted'by g.:.,tit lilfed !ntra!\Sp..;.,;nt Si!.1emnl aggressive agents (wat;:r, chlorides, etc.) over the service life of the structure.
Leak tight connections prevent cement grout leakage and crossovers during grout injection. LIASEAL components are non-metallic, cannot corrode and offer permanent protection to internal tendon prestressing slecl at segmental bridge joints. •
LIASEAL can be used with HDPEIHDPE ducts to provide a complete leak"'tight plastic encapsulation of the tendons.
)
Mechanical engagement
Scre\\ing
Chapter 12.0- Epoxy Jointing. Duct and Duct Coupler Devices, and Prepackaged Grout
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12.3.2 VSL Segmental Duct Coupler
Segmental Duct Coupler 7455-T New Ridge Rd., Hanover, MD 21076- 888-489-2687 www.vsl.net
Design Features: •
Complete encapsulation of post-tensioning tendons through segment joints
•
Small form factor- does not require increased duct spacing
•
Tendons can pass through bulkheads at an angle, resulting in reduced friction
Casting Features: •
Uses conventional inflatable mandrel to support duct
•
Duct does not need to be precisely cut to length
•
Uses standard bulkhead
Bulkhead
Inflatable Mandrel
Coupler Sleeve
j
~
Seals
Erection Features: •
No components projecting from segments during segment erection
•
Segment shimming does not impact coupler performance
Visit www.vsl.net for updated technical data and dimensions Patent Pending
Chapter 12.0- Epoxy Jointing, Duct and Duct Coupler Devices, and Prepackaged Grout
...
8 of 16
)·.
.
12.3.3 General Technologies, Inc.
Precast Segmental Duct and Duct Coupler 13022 Trinity Drive, Stafford, TX 77477 888-255-0440 www.gti-usa.net
New GTI Precast Segmental Duct Coupler
)
GT14 Strand Fully Encapsulated Bonded System
Full Line of Round and Flat Plastic Duct 21mm Grou! Fube
Zero Vofd'/f' -
Monostrond Encapsv/alian w/ Me/a/ Ring
Zerov~
Ccp
Zero vOk::fl?Ccp
Zero Void® Bonded Mono-strand System
Chapter 12.0- Epoxy Jointing, Ductand Duct Coupler Devices, and Prepackaged Grout
9 ofl6
12.4
Prepackaged Grout Prepackaged grouts were developed to reduce or eliminate bleed water voids in the ducts, and to achieve complete filling of the duct with a cementitious grout. Prepackaged grouts are recommended for use on all segmental bridge projects. Even when prepackaged grouts are used, it is necessary to inspect all anchorage areas for bleed water voids within 24 to 48 hours after grouting, until the inspection agency is assured that there are no bleed water voids. Subsequent spot inspections of one or more anchorage per span may be conducted provided no voids are found. Any voids discovered must be filled immediately with cementitious grout, preferably by vacuum grouting.
The cement grout injected into a post-tensioning duct is often the last line of defense against corrosion of the steel tendon. Inspection of the tendons is often difficult, and therefore severe corrosion may go undetected for a long period oftime before failure occurs. The steel tendons are susceptible to corrosion damage because of the high steel stress and the small wire diameter, and if allowed to corrode, there is a danger of structural distress. This underscores the need for the use of quality prepackaged cement grout during the construction of the post-tensioned structures.
Prior to the use of prepackaged grouts, site blended grouts were typically used in post-tensioned applications. The biggest problem with the site blended grouts was the bleed water that would form in the ducts. This bleed water migrates towards the upper end of the duct where it accumulates, and is subsequently absorbed into the matrix. This in turn leaves large voids within the duct containing the cable, and this makes the cable more vulnerable to deleterious chemical attack and/or corrosion. In addition, bleed water itself, and deleterious chemicals that are sometimes admixed, migrate with the bleed water and accelerate strand corrosion. For these reasons, site blended grouts are not recommended for use on segmental bridges.
Post-tensioning techniques There are two types of post-tensioning methods: unbonded and bonded (grouted). An unbonded tendon is one in which the prestressing steel is not actually bonded to the duc1fconcrete that surrounds it except at the anchorage points. In this form of post-tensioning, the tendon (seven-
wire stand) is simply coated with a corrosion inhibiting grease and encased in a plastic protective sheath. In bonded systems, two or more seven-wire strands are installed in steel or plastic ducts in the concrete. The strands are stressed and anchored at a connnon site. After the tendons are
stressed surrounding duct is filled with a prepackaged cement grout that provides corrosion protection to the strands. As seen in Figure 12.5, bonded post-tensioning offers multiple layers of corrosion protection to the steel tendon. Protective measures include surface treatment of the concrete, the concrete itself, the duct, the grout, and possibly, strand or bar coating such as epoxy or galvanizing.
In order for the grout to provide protection to the steel, it should form a good bond between the duct and the steel. A grout having good bond characteristics, transmits forces from the concrete
Chapter 12.0- Epoxy Jointing, Duct and Duct Coupler Devices, and Prepackaged Grout
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.)
Figure 12.5- Multilevel Corrosion Protection for Bonded Post-Tensioning Tendons to the steel over its length, and thereby relieves load stress fluctuations at specific sites. As a result of site-specific load stress fluctuations, grout sections having poor bond characteristics
)
may crack easily thereby creating easy access for the ingress of moisture and deleterious chemicals such as deicing salts. The grout functions to provide corrosion protection by passivating the steel strands due to its high alkalinity, which in turn is provided by the hydration of potassium, sodium and calcium ions in the Portland cement. Complete filling of the ducts with a non-bleed grout ensures that there is no damage due to freezing and expansion of trapped water/moisture, which in turn prevents damage to the external concrete. This can only be consistently achieved with the use of prepackaged grouts having been formulated to have zero bleed. High permeability resistant characteristics of the prepackaged grout ensure that no deleterious chemicals (deicing Cr) have easy access to the encased steel. Chloride ions destroy the passivating iron-oxide layer on the steel surface, which in turn exacerbates steel corrosion. In addition, carbon dioxide from the atroosphere, if allowed to penetrate through the cement grout, could reduce the pH and thereby could lead to loss of passivity, and ultimately, corrosion. Therefore, it is important that the prepackaged grout have a low permeability .
Figure 12.6- Completely filled duct with prepackaged grout Chapter 12.0- Epoxy Jointing, Duct and Duct Coupler Devices, and Prepackaged Grout
II ofl6
Prepackaged Epoxy Grouts for Anchorage Zones Prepackaged epoxy grouts are designed to seal and protect the anchorages of post-tensioned tendons on segmental bridges. This is the area that is the most critical for post-tensioned bridges since it is completely exposed to the elements. If site batched cementitious grouts are used for the "pourbacks," they can shrink and crack over time, allowing moisture and chlorides to gain direct access to the steel strands, and over time, initiate the corrosion process. Prepackaged epoxy grouts offer the following benefits: • •
Pre-measured kits (no mixing errors) High bond strength
•
Non-shrink
• • •
Low exotherm Impermeable to moisture, chlorides and chemicals Resistant to impact, vibration and stress
) Figure 12. 7- Prepackaged epoxy grout poured into anchorage zone
Details on commercially available, prepackaged grouts are presented in Sections 12.4.1 and 12.4.2
Chapter 12.0- Epoxy Jointing, Duct and Duct Coupler Devices, and Prepackaged Grout
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12.4.1 BASF Construction Chemicals- Building Systems Epoxy and Prepackaged Grout for Segmental Bridge Construction
D•BASF The Chemical Company
Bridge Products By BASF Construction Chemicals - Building Systems Building Bridges for Durability
1. Corrosion Protection for PT Strands. Complete fill and protect PT ducts with Masterflow® 1205 distances.
cable grout.
High-flowability, easily pumped long
2. Bearing Pad Grouting - Highly flowable leveling grouts.
Masterflow® 928.
Easy install, especially in hot weather conditions
3. Protect PT Anchorage Blocks Coat with Sonoguard® Top Coat, flexible urethane waterproofing. 4. Patching P-T block outs and inspection points use Weather" rapid set.
)
"Set 45 Hot
5. End anchorage caps corrosion protection- Encapsulate caps with Masterf/ow® 648 CP Plus epoxy grout. 6. Anti-carbonization Coating Thorocoat smooth, a pure acrylic coating. Exceptional long-life, rich custom colors for beautiful bridges.
7. Segmental Epoxy Adhesives - Concresive® SBA 1440 series
Protection for 8. Chloride Concrete "Enviroseal 40" Silane waterbased penetrating sealer. 9. Bonding Bridge Overlays & cold joints, Concresive Liquid LPL epoxy. lO.Key Way grouting "Set® 45" magnesium phosphate based concrete. Non-shrink, chloride resistant and rapid setting even in freezing temperatures BASF Construction Chemicals - Building Systems 889 Valley Park Drive Shakopee, MN 55379 Customer Service 800-433-9517 Technical Service 800-243-6739
Chapter 12.0- Epoxy Jointing, Duct and Duct Coupler Devices, and Prepackaged Grout
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12.4.1 BASF Construction Chemicals - Building Systems Epoxy and Prepackaged Grout for Segmental Bridge Construction
D•BASF
Bridge Repair
1. Crack Repair of Structural Elements Concresive® Standard SLV epoxy used for injection grouting of fine cracks. Structurally bonds concrete.
The Chemical Company
2. Heal and Seal Map Cracked Decks. Concresive® 2070 Methacrylate penetrates cracks, seals bridge decks and gets traffic lanes reopened with hours of application. 3. Repair Concrete Pavements, Bridge Decks, and Resurface Traffic Lanes - "Emaco® T-430" and "Thoroc SD2" mortar. 4. Dowel Bar Pinning of Joints in Concrete Roadways - Dowels are installed to pin jointed pavement sections together for the purpose of preventing bounce (and resulting wear) between pavement sections. "Set® 45" Manesium Phosphate based concrete. 3000 PSI in 1 hour. Non-shrink. 5. Piles, Pier Sections, Girder Repairs Three types of repairs are most common: • Small spalls - Emaco S88 silica fume mortar & Thoroc® HBA non-sag mortar. • Larger isolated areas - damaged caused by impact (over height vehicles) on the underside of Beams, Spalling caused by corroding steel reinforcing, deck areas joints. including spalling expansion Typically a highly flowable, shrinkage compensated, low permeability repair mortar is desirable. These mortars can for PUMPED or Poured into formed spaces. Good choices for beam and girder repair include "Emaco 566", "Thoroc LA 40" flowable, fast setting repair mortars. • Large area I volume repairs - vertical and overhead (not pavements), i.e. bridge abutments, protective seawalls, bascule bridge structures, piles etc .... Shotcrete repairs are often the best solution. Use "Shotpatch® 21F". 6. Corrosion Inhibiting Passive Galvanic I Cathodic Protection: Corr-Stops® easily installed zinc based corrosion mitigating anodes. BASF Construction Chemicals - Building Systems 889 Valley Park Drive Shakopee, MN 55379 Customer Service 800-433-9517 Technical Service 800-243-6739 Chapter 12.0- Epoxy Jointing, Duct and Duct Coupler Devices, and Prepackaged Grout
,~) 14 of 16
12.4.2 Sika Corporation Epoxy Resins for Segmental Bridge Construction Sika Corporation 20 I Polito Avenue Lyndhurst, NJ 07071 Tel: (201) 933-8800 Fax: (201) 933-6225 Email:
[email protected] Web: www.sikaconstruction.com Sika Corporation is a worldwide leader in the construction industry specializing in systems for concrete repair, protection and structural strengthening. Sika offers products such as concrete admixtures, corrosion inhibitors, repair mortars, prepackaged grouts, sealants, adhesiveS, c0atings, and segmental bridge epoxies. Sikadur 31, SBA (Segmental Bridge Adhesive) has been used on most of the segmental bridges constructed in the United States and around the world. The specially formulated epoxies are available in Normal Set and Slow Set formulations for use in temperatures from 20 degrees F to 115 degrees F. Sikadur 31, SBA is a unique high-modulus, 2-component, moisture-tolerant, solvent free, epoxy resin. It conforms to the current ASTM C-881 requirements and ASBI Guidelines for epoxy resins. The range of products is as follow:
)
Normal Set
Slow Set
Sikadur 31, SBA (20-45F) Sikadur 31, SBA (40-60F) Sikadur 31, SBA (55-95F) Sikadur 31, SBA (80-115F)
Sikadur 31, SBA Slow Set (40-61F) Sikadur 31, SBA Slow Set (55-75F) Sikadur 31, SBA Slow Set (70-90F)
Figure 12.8- Applying Sikadur 31, SBA on Central Artery Bridge in Boston, MA
Chapter 12.0- Epoxy Jointing, Duct and Duct Coupler Devices, and Prepackaged Grout
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12.4.3 Sika Corporation Prepackaged Grouts for Segmental Bridge Construction SikaGrout 300 PT is a high performance, zero bleed, sand-free, non-shrink cementitious grout with a unique 2-stage shrinkage compensating mechanism. It is non-
metallic and contains no chlorides. With a special blend of shrinkage-reducing and plasticizing/water-reducing agents, SikaGrout 300 PT compensates for shrinkage in both the plastic and hardened states. SikaGrout 300 PT is designed for use in horizontal and vertical grouting of ducts within bonded, post-tensioned structures. It can also be used to repair voids within ducts of post-tensioning strands for corrosion protection. With its high fluidity, SikaGrout 300 PT can also be use for grouting in tight clearances.
Figure 12.9- SikaGrout 300 PT being used in Segmental Bridge Construction Sikadur 42, Grout-Pak PT Sikadur 42, Grout-Pak PT is a prepackaged, three component, !00% solids, moisture tolerant epoxy grout specifically designed to seal and protect the anchorages of post-tensioning tendons on segmental bridge projects. Anchorage locations are commonly referred to as "pour-back" boxes. Sikadur 42, Grout-Pak PT is an impermeable epoxy grout that is resistant to chemicals, corrosion, impact, vibration and stress. Even when poured in mass, Sikadur 42, Grout-Pak PT has a low peak exotherm, meaning it safely cures with low heat development. It is a non-shrinking grout providing high compressive strengths.
Figure 12.1 Oa -Post-tensioned strand terminus
Figure 12.1 ObSikadur 42, Grout-Pak PT mixed in pail
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TABLE OF CONTENTS
CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 13.0 GEOMETRY CONTROL
13.0 13.1 13.2 13.3 13.4 13.5 13.6 13.7 13.8 13.9 13.9.1 13.9.2
•...
Geometry Control General Casting Cell Geometry Control System Tools Used for Geometry Control Geometry Control of the First Pier Segment Field Survey Checking During Erection Systematic Error Achieved Profiles Pier Shaft Segments Temperature Effects Temperature Expansion and Contraction Temperature Gradient
3 3 7 12 13 13 14 15 15 15 15 18
) Chapter 13- Geometry Control
I of 19
TABLE OF FIGURES
CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 13.0 GEOMETRY CONTROL
Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure
13.1 13.2 13.3 13.4 13.5 13.6 13.7 13.8 13.9 13.10 13.11 13.12 13.13 13.14 13.15 13.16 13.17 13.18 13.19 13.20
4 4 6 7 8 8 9
Alignment Control: Set-Up Alignment Control: Set-Up (Continued) Setting Pier Segment from Ground Definition of Global Geometry Match-Cast, New-Cast and Bulkt)ead Joint in Global Structure Segments in Local Casting Cell Coordinates Cell Hardware and Survey Observations After-Cast Survey Observations- General Case A check for twist of the Match-Cast Segment Geometry Control Measuring Equipment Geometry Control for Starting (Pier) Segment Effect of Accumulation of Systematic Errors Alignment of Cantilever Structure (Three Span) Alignment of a Span-by-Span Structure Shimming Joints to Correct Profile Shimming Joints to Correct Profile (Continued) Geometry Control for Precast Pier Shaft Segments Temperature Expansion and Contraction Temperature Gradient Deflection Caused by Temperature Gradient
Chapter 13 - Geometry Control
10 11 12 14 14 15 16 16 17 17 18 19 19
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13.0 Geometry Control 13.1
General The geometry control of precast segmental bridges is achieved io the casting yard. The "shortline" casting system is based on making very fine adjustments to each match cast segment in the casting cell, and therefore requires precision; more so than the 11 }ong-line" system where the geometry control is maioly achieved when building the soffit. The following discussion concentrates on the "short-line" system since it is more commonly used, although the principles apply to both systems.
Precision geometry control has nothing to do with the sizes, thickness variations or tolerances of the component pieces of the segments, important though as these are to the overall quality of the finished product. The precision is required for measuring the relative as-cast position of the new segment in relation to its match cast neighbor. These measurements are critical. The setup required for this io the casting yard is shown in Figure 13.1. The aligmnent is controlled by an instrument on a permanent base and a permanent target. Neither instrument nor target should be disturbed throughout the production, otherwise control must be reestablished. For this, adequate bench marks should be maiotained. The casting cell is always plumb, level and usually square so the geometry control is established, mainly by positioning the old segment as prescribed by the castiog curve and as shown in Figures 13.2(a) and (b).
)
As the first segment is cast and the top slab has been fmished, four elevation bolts, A, B, C, and D, as well as two centerline markers, E and F, are installed. The following morning, the elevations of the tops of the bolts are recorded and the centerline is scribed onto the centerline markers. Now the segment can be rolled forward for match casting. After the first segment is moved to the match casting position, it is reset to the instructions provided by the casting curve. The centerline will be as it was before, unless the bridge is curved. In case of a curved bridge, an offset "0" is used as shown in Figure 13.2(a). The vertical curvature is handled similarly. But even if the bridge is flat, it is necessary to adjust for the deflections which occur during construction. As mentioned, the amount of adjustment to be made is determined by the casting curve which can be part of the shop drawings. Note that if the segment would be positioned in such a way that both centerline markers are in line with instrument and target and the bolt elevations are the same as those measured before the segment was moved, the segment would lioe up exactly with the next segment-to be poured. Geometry control for precast segmental bridges requires an excellent surveyor. He should be on the job daily and keep accurate records. In spite of his competence, his work should be meticulously checked by the inspector since errors are expensive and time consuming to correct. After the old segment is properly reset and the setup for the new segment is complete, the new segment can be cast. The following morning, the surveyor marks the center line and records the bolt elevations of the new segment. In addition, before the old segment is moved, the elevations of its bolts and its centerline position are checked to determine if the old segment has moved during casting the new segment. It is often noted that position changes of the "old segment" occur due to settlement of the soffit rails by the segment weight, due to vibrating of fresh concrete against it, or due to forces applied to it while closing the forms.
Chapter 13 - Geometry Control
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"'f>'·
level boll
Old ,...gment
N.e w SErgment
---
-
lllS'lrument
llorbtoni.,J refe#Wl!Cf!
Levt!!l boll Ne-w .segment.
~;:S:~~;:~p=lo~ne
__________~-, OM segment
ELEVATION
Figure 13.1 -Alignment Control: Set-Up
/n•
Cenler line
•A IE
.
Form always
plumb, level
~c
ll.J
square
Segment rotalion
Amount of offset determines horizontal
·o·
curvature
Level bolls ~
n
-
1 ~Target
anrl usually
(a)
Old segment
-
lJ.
•Ne. w ..
'(b)
'
B D
1
"old"
Amount of till
rcurva l ure
l-r·
El.EVAT[(JN
Figure 13.2 -Alignment Control: Set-up (Continued)
Chapter 13 -Geometry Control
-r-
det-ermines vertical
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When constructing a bridge using girders or whole spans cast in place, it is normal practice to set forms to within 1/100 feet (1/8 inch) of the desired position duly corrected for anticipated deflections. Each new segment should be cast to stay within this tolerance based on as-cast surveys of the previous segments. As accuracy depends upon consistency, it is important that the same individuals make the critical"as cast" observations at the same time each day prior to stripping the forms ofboth the new and the old match cast segments. Usually, this is the first thing each morning before the daily crews arrive and when weather conditions are most stable from day to day. Note that all the critical readings are those after casting. While it is important to have an accurate set up before casting, this is unlikely to remain so during the casting operation. Some movement,
however slight, will occur, so the true achieved geometry is recorded after casting. It is possible to compensate for casting errors by adjusting the position of the next set up and so on. In fact, the major challenge in geometry control lies in keeping track of casting errors and correcting for them. Erection of the first segment, usually a pier segment, is critical and should be done as accurately as possible. This segment should be placed to an accuracy of Ill 000 feet. It is very important that all the information from the casting operations and the calculated "as cast"
actual relative positions of the segments be carried through the field erection process as well. This poses some practical difficulties because it is by no means as easy to obtain the same accuracy in the field as in the casting yard. However, the field setting is only required at each pier segment or start of a successive run, and it is worthwhile doing this correctly. Placing a large chunk of concrete with a crane to an accuracy of a few thousandths of a foot is difficult. In practice, it is possible to use shims, packs and wedges to maneuver the segments to an acceptable
)
accuracy. Also, by installing supplementary transverse alignment markers while in the casting cell, the horizontal adjustment ofthe pier segment can be set in the field using the base line of the full segment width, thereby not relying solely upon the shorter, front to back; longitudinal centerline marks (Figure 13.3). During erection, elevations and horizontal alignment should be checked to see if they are in agreement with the calculated as cast positions. If not, then adjustments may be necessary. Such compensations include: re-orienting or rotating the cantilever after erection, calculating a
compensatory setting for the next cantilever, or shimming the joints. The latter should only be used as a last resort as it can unpredictably lead to "correction of corrections," and so on. Moreover, it is not effective for short cantilevers or deep girders.
Chapter 13 - Geometry Control
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liPrizont'BI' n.figumeul: -cont-rol by observation onlo P-I'e-sel lrt~nsverse
een-lertine
\
Figure 13.3 - Setting Pier Segment from Ground
Precision within the geometry control system is essential in order to avoid errors in the geometry of the structure. A source of error in aligmnent may arise from the deformation characteristics of the concrete being different from those assumed. Deformations of concrete are difficult to predict with any degree of accuracy, and most attempts are, at best, sophisticated judgments. In segmental construction the actual deflection can differ from the theoretical just as in precast girder production, where identical girders can differ in camber by a few inches. However, with precast segmental construction most of the shrinkage has usually occurred during storage, and the concrete has matured substantially by the time of erection. This helps to eliminate the significant variations likely with young concrete.
Chapter 13 -Geometry Control
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13.2
Casting-Cell Geometry Control System
Geometry control is achieved in the casting cell by means of a system illustrated in Figures 13.1 and 13.2. The elevation control bolts A, B, C, Din Figure 13.2 are set over the webs as these are stable locations where no vertical deflection occurs from transverse flexure or post-tensioning. For example, wing tips can sometimes deflect upward by Y. inch from post-tensioning. Horizontal control is established by setting the match cast segment at the necessary skew at offsets measured at centerline hairpins E and F. Vertical alignment is set by adjusting jacks on the soffit carriage of the match-cast segment until the elevation bolts are above or below the plane of the top of the bulkhead by a desired amount. Normally, the geometry of a segmental bridge surface is defined by establishing three dimensional global coordinates (easting, northing, and elevation) at the centerline and equidistant to the left and right over each web at each joint (Figure 13 .4). These coordinates are directly calculated from the stationing, Instantaneous radius of curvature, longitudinal profile grade and snperelevation at each joint. Global elevations are adjusted for camber (the opposite of deflection). Normally, camber adjustment for global structural torsional twist is rarely needed but could be incorporated if necessary.
Geometry Control: 30, Define Structure Geometry
Global
v"""""
/
'
j'
Global Coordinates: E, N, Z at left, center, right at each joint
Figure 13.4 - Definition of Global Geometry
Chapter 13 -Geometry Control
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Three consecutive joints defme the intrinsic geometric surface shape of two consecutive segmentsnamely: the previously made match-cast segment and the yet to be made new-cast segment.
Geometry Control: Relation Global Space to Cell Up
Station
Match Cast (M) and New-Cast (C) in Global Space
Figure 13.5- Match-Cast, New-Cast and Bulkhead Joint in Global Structure Geometry Control: Relation Global Space to Cell
Match Cast (MC) and New-Cast (NC) in Local Cell
Figure 13.6- Segments in Local Casting Cell Coordinates
Chapter 13- Geometry Control
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)
If it is assumed that the after-cast coordinates of the match-cast segment are already known from previous observations and calculations, it is a tedious but relatively straightforward mathematical process to imagine setting the cell-bulkhead at the desired position of next (new-cast) joint in global space (Figure 13.5) and transforming the global coordinates of the two known joints and the new desired (bulkhead) joint from 3-D global space to the local coordinates of the casting-cell. The latter are defined by the bulkhead and cell centerline (Figure 13.6). This transformation provides the set-up of the match-cast segment relative to the desired bulkhead location for the new-cast segment. To reference the new segment to the cell and facilitate after-cast observations, four new elevation bolts and two new centerline hairpins are placed in the top of the new-cast segment, close to match-cast joint and bulkhead. Those close to the bulkhead (bolts Ao and C, and centerline pinE,) define the position of the bulkhead joint. Those close to the match-cast face (bolts B, and D, and centerline pin F ,) relate directly to those next to them on the match-cast segment (Am, Cm and E.,) and thus to the previous bulkhead joint. Likewise, those at the far end of the match-cast segment (Bm. Dm and F.,) relate to the previous (A", C" and E" -not shown) and the previous bulkhead joint.
Geometry Control: Survey Hardware
r"rEie,effon Bolts
(Vertical Control)
Cefl
L..
Bulkhead
Face
'-''""'""on Top of Bulkhead (Typ.)
(shown for bulkhead perpendicular to chord)
Geometry Control Survey Hardware in Local Cell
Figure 13. 7- Cell Hardware and Survey Observations No set-up is ever perfect and match-cast segments always tend to move a little during casting. So, after casting, all bolt elevations are carefully surveyed relative to the elevations at the top of the bulkhead. The centerline of the casting cell is punch-marked into the centerline hairpins on the new-cast segment. Theoretically, these have an offset of zero (Figure 13.7) providing there is no mistake when punching. Regardless, all four centerline hairpin offsets are measured from the casting cell centerline. The length of the new-cast segment is measured along the webs between like-bolt (i.e. Ao to Am and from C, to C.,) - the average is used for the centerline length. This requires that all bolts always be set at a constant, short distance from the joints - and likewise the hairpins. And that elevation bolts always be a a constant distance ("W/2'') from the centerline. For length measurement, the same center-punch marks are used in the elevation bolts as used for setting the point of the survey leveling rod. Figure 13.8 summarizes the necessary after cast observations and includes the general case of a deliberate, or accidental, non-zero center offset at the match cast joint.
) Chapter 13 - Geometry Control
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Geometry Control: After-Cast Observations
Joint jj Previous
Ch Match-Cam Segment
Sight-line
Center Hairpin
A
Jomti
LeftLe
Ceil Left
Em
em
'=======~~-~m==~~~~--==~~~~-====--1 ~ B.c De New-cas!
Segment
Cell Righi
Right Length =Cctocm
cb
Standard 'd'
Fixed
Bulkhead
Non-Zero Offsets - regardless of radial or perpendicular
Figure 13.8- After-Cast Survey Observations- General Case Survey results are converted into coordinates local to the cell itself and then local to the cell-axes of the match-cast segment when it was newly cast. Using these match-cast cell-axes as a reference enables transformation from the cell to global space and provides the actual achieved "as-cast" location of the new bulkhead joint. The entire process is repeated for the next segment, and so on. This process- "3-D Coordinate Geometry Transformation Technique" -was originally developed at the Linn Cove Viaduct in 1979. For simplicity of construction and ease of operation, casting cells are almost always fabricated so that the bulkhead is perpendicular to the cell centerline. Also, the soffit form is rectangular and the web and wing forms operate parallel to the cell centerline- as in Figure 13.7. Horizontal aligmnent is attained by slewing the match-cast segment in plan- holding the centerline offset at the match-cast face at zero - while offsetting the far end face (remote from the bulkhead) by the desired geometric amount. This configuration places the bulkhead joint face perpendicular to the chord conoecting the centerline points of the new-cast segment. The resulting joints in the bridge are not on a radial line but are perpendicular to the chord- i.e. slewed off-radial one way or the other depending upon the direction of casting. Such joints are often referred to as "chord-perpendicular joints" as opposed to the alternative of "radial joints". For the general condition of any type of curvature, the calculation of global 3-D coordinate geometry is relatively sirople when joints are truly "radial" (Figure 13.4). However, in order that casting cells remain simple machines it is necessary to modify coordinates generated on a radial to chord-perpendicular coordinates prior to perfomting transformations from global space to the cell and vice-versa. The mathematical exercise involves interpolating (in 3-D) along the longitudinal lines of the left and right elevation control points, with some iteration, until the global coordinates of the joint lines are mutually perpendicular to the centerline chords. Since the direction to slew the joint depends upon the necessary or Contractor's elected direction of casting, this part of the process may await the actual casting. In the meantime, for information and geometry planning it is useful to have three-dimensional coordinates generated for radial joints provided on design plans - since this is the first step in a general process.
.J Chapter 13 - Geometry Control
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Observations are made to an accuracy of ±(J.OOl feet. It is recommended that readings are by two separate teams or lead surveyors. The alignment of the cell and elevation and attitude of the bulkhead should be checked regularly by reference to remote bench marks or survey points to guard against (unlikely but possible) error due to drift of equipment. Processing of numbers may be graphical or numerically by computer. It is recommended that a graphical plot to an exaggerated scale be run as a separate check against computations and to provide a visually recognizable warning in advance of error.
The above is a basic introduction to geometry control needs and techniques. It is not the intent here to present a full thesis. Geometry control calculations are tedious; they are best made by a computer program and further explanation would add little to this guide. Variations on the basic process are possible to accommodate situations where occasional elevation bolts and centerline hairpins cannot be placed in their desired locations to avoid construction details such as block-outs - or to accommodate breaks in superelevation across the width of the segment or an offset profile grade line - and so on. The key is always to respect that elevation bolts over the webs defme vertical control and centerline hairpins define horizontal control.
It is important that little or no twist is inadvertently introduced when moving a new-cast segment into the match-cast position- a simple check is illustrated in Figure 13.9
Geometry Control: Twist Error Twist: Set-Up of Match-Cast Segment Desired setting
~"'I :?>"'" - - -- -'
Inadvertent twisted setting
------.'it
G>·-----------------------.. .· ............... Bulkhead
For no twist set-up, check elevations: (Dm- Cm) +(Am- Bm).LAB = [De- Cc] + [Ac- Bc].LAB LCD LCD
Figure 13.9- A check for twist of the Match-Cast Segment
Chapter 13 - Geometry Control
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13.3
Tools Used for Geometry Control (I)
Offsets: Centerline offsets are measured from the casting cell centerline using a metal scale fitted with a center point which sits in a pnnch mark on the hairpins. A spirit level shonld be attached to this scale so that it is set horizontal. Also, it should be held at right angles to the centerline of sight in the cell (Figure 13.10).
(2)
Elevations: Elevation readings on the bolts are made with a precision level placed on top of the fixed mounting, reading onto a leveling rod fitted with a scale divided down to at least .005 feet. In order to make sure the readings are taken at exactly the same point each time, the leveling rod should be fitted with a center point which sets into a punch mark in the top of the bolt.
(3)
Lengths: A steel tape is used for length measurement. It is advantageous to measure lengths between the center point marks on the hairpins, the distance between, adjacent hairpins and similarly along the bolt lines between the leveling pnnch marks. Readings should be estimated to at least .002 feet for length (Figure 13.8).
(4)
Lateral offsets to the level bolts should be measured from the centerline hairpins. It is preferable to have the bolt positions accurately marked on the bulkhead so that they are always at the exact required offset from the centerline (Figure 13.8). With care and precision, the readings obtained will allow precise processing using threedimensional coordinate geometry computations which are the most accurate when it comes to defining curved surfaces in space. Good recordkeeping is essential as well. There have been occasions when accidentally one or more of the geometry control hairpins or bolts were lost. This is not irretrievable. It is usually possible to continue construction by using known relative positions of adjacent undamaged markers. What it means is merely a little less predictable control over the erection aligmnent.
Spirit levelling bubble
~
Pfnely divided metal scale
I
pirit level.
~
~
~
. Cenler point c( ha,.,dend sl'eeJ
Center punc!J stirrup
HoNZ!J!!Iaf Qflsel$
Cenl-er point of h~t:delJ
ed steel ___
·an ball -
Figure 13.10- Geometry Control Measuring Equipment Chapter 13 - Geometry Control
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13.4
Geometry Control of the First Pier Segment The first segment of a run or a cantilever is cast between the bulkhead and a temporary bulkhead. Consequently, it has no match cast segment to which its geometric position can be referenced.
When moving this segment from temporary storage into the match-casting position, it is simply set to the same position it had after casting by reading the same elevation on the bolts and the same offsets on the markers; This gives a starting point from which all other segments can be subsequently referenced, assuming that there is no casting curve adjustment to be made. If there is a casting curve adjustment needed, it can be made at this time. The bolt and centerline marker readings are also used for setting the first segment in its required attitude in the erected structure. The technique is again part of regular geometry control procedures and will not be elaborated further here. The main feature of the first segment which, if it is a pier or abutment segment, is usually shorter than the typical segments, is to establish a transverse horizontal control line on the surface of the segment in the casting cell (Figure 13.11 ). This provides a greater base line length to align the segments in the field. The normal procedure is to determine either a radial line or a line parallel to the bulkhead and establish this on the center of the segment with horizontal alignment hairpins set as far out on the segment wings as possible. This requires that this line be observable on the bridge, either from above or from the ground below. In the latter case, the line has to be scribed onto the end faces of the wings, and two observation stations must be established on the ground on either side of the pier (Figure 13.13). Precise setting and checking of the first erected segment is essential since any error in its position
is magnified proportional to the ratio of the length of the cantilever or continuous run of segments and the transverse base line width.
) 13. 5
Field Survey Checking During Erection After the pier segment has been set and checked the horizontal and vertical alignment of successive segments must be checked as well. It is normal practice to calculate and measure elevations each time each segment has been erected. The horizontal alignment is also checked and
should match the theoretical horizontal geometry. The only errors occurring should be slight deviations due to casting errors and corrections. The overall line should closely track the desired
line. A generous tolerance should be allowed for the vertical alignment since this is subject to all kinds of variations due to construction loads, creep, shrinkage, temperature, post-tensioning variations,
and so on. However, the alignment should closely agree with the required alignment at the time of erection when duly corrected for these effects. It is difficult to put a precise figure on this tolerance as it depends upon the type of construction. For cantilever construction, the vertical
alignment should generally be within one- to two-inch per cantilever length of I 00 feet, and similar cantilevers should behave comparably. (This latter point is a guide to the accuracy of the initial material assumptions and calculations). Any substantial variations from line and level or any trends noticed early in the construction
should be subject to close study, and corrective action should be taken. The latter would include checking procedures for errors, especially systematic errors, amending casting curves for future
segments and perhaps shimming the joints with glass fiber matting to adjust the alignments. The use of shims is a "last resort" since it causes stress concentration on the segments and prevents the
joints from closing properly, which may cause problems during grouting.
Chapter 13 - Geometry Control
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Pre-determine and set lhis angle in the casling--cell
f f. C;rsling-cell - ----~
£1e•,.L1on bolts
I
I
...- Tempornry
lmlkl!ead
•
- [-.
.. Auxiliary llD irpins to_/ ll"iiiJSflei"'Se £
Casting-eel/ bulk/lead
scl
Alain longitudinal center line hairpiiJs
Figure 13.11- Geometry Control for Starting (Pier) Segment
13.6
Systematic Error It is worthwhile giving some consideration to the implications of making a systematic error in each casting operation either as a result of a computational method error or as a physical defect of the equipment which is systematically repeated in each segment of a nm. Figure 13.12 shows the effect which creates a total small systematic error (e). The final error after "n'' segments amounts to n(n-1 )e/2. In other words, a systematic error of .002 feet in each segment would amount to an off line error of .09 feet after 10 segments and .38 feet after 20 segments. Clearly, systematic errors must be avoided, and the use of proven techniques should be encouraged. e::;t•rror
---r
n-1
E
___L It can be_ slioivn lllal tile effect of
error
E.
1'1
sm
