Connections for Steel Structures by John Mark (CISC - ICCA)

CALGARY 3 APRIL 2012

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CONNECTIONS FOR STEEL STRUCTURES John Mark P.Eng.

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Steel Handbook 10th Edition 2010

Connection Reference CSA S16-09

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COURSE AGENDA 1. 2. 3. 4. 5. 6. 7. 8. 9.

Introduction Bolts and Welds Types of Construction Permitted Economics Types of Connections New Connection Guidelines in CSA S16-09 Connection Comments Summary Q&A

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CONNECTIONS FOR STEEL FRAMED STRUCTURES Structural Analysis:

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Connection Design & Detailing

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CONNECTIONS FOR STEEL FRAMED STRUCTURES

As Built Connection

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BOLTS & WELDS

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STRUCTURAL BOLTS A307 A325 A490 Heavy Hex

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..and equivalents F 1852 F 2280

A325 A490 Heavy Hex

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…there’s a new kid on the block! the SUPER HIGH STRENGTH BOLT • A325 at 830 MPa • A490 at 1040 MPa • X??? at 1400 MPa

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……threads in the shear plane or not ?

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Twist - Off Assembly…...

………as delivered

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Use of DTI Washers ASTM 959

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Shop Welding Welding performed under controlled conditions 15

Field Welding Welding performed under varying conditions 16

Weld Metal • Weld electrodes are selected to “match or overmatch” the specified minimum tensile strength of the base metal (CSA Standard W59). • The term Xu is the electrode’s tensile strength • E49XX electrodes, Xu = 490 MPa.

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Basic Weld Types

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Shear strength of welds •

• •

Weld resistances use a resistance factor = 0.67, lower than 0.90 that is used for the resistances involving the base metal to preclude the failure of the weld before that of the main material. Weld failures do not involve large deformations. Therefore a higher margin of safety against weld failures has been traditional practice in codes and standards.

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Factored Resistance of Fillet Welds for Direct shear or Tension/Compression Induced Shear

Where Ɵ = angle, in degrees, of axis of weld segment with respect to the line of action of the applied force, 00 for longitudinal weld and 900 for a transverse weld. Mw = strength reduction factor for multi-orientation fillet welds

Base metal check is not required for design of fillet welds. 20

Fillet Weld @ 90 Degrees to Force

Vr = 0.67x0.67x4.24x.490x1.5 x1.0 = 1.3995 kN/mm or 1.40 vs (1.21 kN/mm) 16% 21

CSA S16-09 permits three construction types

Construction Types

• 8.2.2 Rigidly connected and continuous construction

• 8.2.3 Simple construction

• 8.2.4 Semi-rigid (partially restrained) construction 22

Economics

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Economics •

Strength, serviceability and overall cost.

•

Fabrication costs are influenced by the amount of: cutting, hole making, fitting, handling, assembly and joining of detail material to main material. (Therefore fabrication costs are directly influenced by the complexity of detail.)

•

Erection costs are influenced by the time to erect, plumb and complete the connections.

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Economics Simplified economical cost breakdown of Structural Steel Price: Material:

33%

Fabrication: 33% Erection:

33%

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Connection Behaviour •

Connections permit forces to travel to adjoining members to relieve the effects of local stress concentrations at the member intersections or to stabilize certain compression elements.

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Complexities of connection behaviour cannot be readily analyzed by conventional means.

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Based on research, rational models and procedures have been developed for analyzing connections and simple rules have been established for proportioning connection components 26

Connection Design

Should not be approached as an exact science •

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The designer should carry out a rational analysis to determine a realistic distribution of forces within the connection. Failure modes for the connection must be established and are usually based on a simple concept of “force paths” The designer must ensure that each component of each force path has sufficient strength and stiffness to transmit the required forces 27

SEVERAL EXAMPLES OF TYPES OF CONNECTIONS

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SIMPLE SHEAR CONNECTIONS

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SIMPLE SHEAR CONNECTIONS

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Shear Tab

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Bracing Connections

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Column Connections

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Moment Connections

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Truss Connections

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HSS CONNECTIONS

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CONNECTIONS FOR STEEL FRAMED STRUCTURES

New for CSA S16-09 re: connection design

Clause 27 (Seismic Design) is not covered in this course 38

New clause CSA S16-09, Clause 13.11

Block Shear Strength Tr = Øu[UtAnFu+0.6Agv(Fy+Fu)/2] Ut = efficiency factor per connection type An = net area in tension Agv = gross area in shear 𝜙𝘶 = 0.75

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Bolts in Bearing & Shear, Clause 13.12.1.2

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fastener shear strength can only be achieved if sufficient BEARING STRENGTH is there • •

now we must look at the material of the connected member to provide local strength to develop shear this bearing strength saw major revisions in the 1970’s when it was expressed in terms of the Fu of the connected plate

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The bearing is now linked to tear out • There is no longer a “poison bolt” Br = Φ n e t Fu • Bearing has a higher resistance factor Φ = 0.8 Long slotted holes have a reduced (80 %) bearing strength….. Br = 2.4 Φ n d t Fu • Tear out tends to be a “small” connection problem - make them larger; avoid minimum gage/pitch • Many new mechanisms for tear out are now recognized • …..but why do new equations for block shear keep appearing? 42

the questions of tear out strength • What does the ultimate state look like? • Can tensile and shearing strengths occur simultaneously? • If not we need to factor to include the effect.

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Shear through the threads or not

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Resistance of M/D fillet welds, Clause 13.13.2.2

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Example (summary) Per S16-09 Trans. weld

= .933 x 1.5 x 1.0 x 100

= 140 kN

Long. welds

= .933 x 1.0 x 0.85 x 600 = 476 kN Total = 616 kN Previous method A = 1.21 x 100 + .933 x 600 = 681 kN (about 11 % higher)

Previous method B = 0.933 x 700

= 653 kN

(about 6% higher)

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Welds & Bolts in Combination, Clause 13.14

Vr = the largest of:

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Example

Determine Pr = ?

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Example Solution

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Bolts in Bending (Fills), Clause 21.8.1.2 In bolted splices the designer can now account for the bending of the bolts

Rv = 1.1 – 0.0158t Rv is the bolt reduction factor, t is the thickness of the fillers Valid from t = 6.4 mm up to t = 19 mm

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Column Splice Fillers

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Fills with Bolts Example; Using 13 mm of loose fills, Rv = 1.1 – 0.0158 x 13 = 0.895 Therefore 89.5% of the applicable bolt shear is allowed And at 19mm of loose fills, Rv = 1.1 – 0.0158 x 19 = 0.80 or 80% of the applicable bolt shear value Research on thicker loose fill plates is continuing 53

Shear Resistance of Col. Webs, Clause 13.4.2 & Clause 21.3

If Vr calculated from Clause 13.4.2

(= 0.8𝜙AwFs )

is exceeded, the column section should either be changed to one with a heavier web or appropriate web reinforcement must be designed.

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CONNECTION COMMENTS

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CONNECTION COMMENTS

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CONNECTION COMMENTS

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Typical Stiffener Details

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CONNECTION COMMENTS

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Connection Forces

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CONNECTION COMMENTS

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SUMMARY • • • • • •

Don’t always stick to least weight design Visualize how pieces can be connected Lines always connect Reduce stiffeners where feasible before tendering Don’t have small lightweights resist large reactions Talk to your friendly fabricator

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QUESTIONS?

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