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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. Introduction

2. Bolts and Welds

3. Types of Construction Permitted

4. Economics

5. Types of Connections

6. New Connection Guidelines in CSA S16-09

7. Connection Comments

8. Summary

9. 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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A325 A490 Heavy Hex

..and equivalents F 1852 F 2280

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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

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Field Welding

Welding performed under varying conditions

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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.

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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%

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Construction Types CSA S16-09 permits three

construction types

• 8.2.2 Rigidly connected and

continuous construction

• 8.2.3 Simple construction

• 8.2.4 Semi-rigid (partially

restrained) construction

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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.

• Complexities of connection behaviour cannot be

readily analyzed by conventional means.

• Based on research, rational models and procedures

have been developed for analyzing connections and

simple rules have been established for proportioning

connection components

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Connection Design

Should not be approached as an exact

science

• 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

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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

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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?

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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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49

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

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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?