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