Steel Connections
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Transcript of Steel Connections
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Steel ConnectionsDesign Issues
Dr. Seshu Adluri
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I d iIntroduction
Steel ConnectionsUnlike concrete, connections in
steel structures need special designp gBolts, Rivets and Welds are typical
connectorsconnectors
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J i i St t l l tJoining Structural elements
Mechanical fastenings Mechanically formed joints Mechanically formed joints Welding
Adh i b di Adhesive bonding
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MECHANICAL FASTENINGSMECHANICAL FASTENINGS
RivetsB lti Bolting
Stud Welding Powder-Actuated Fastenings Powder-Actuated Fastenings Threaded Fasteners & Nails Expansion Boltsp Adhesive-held fasteners Mechanically formed joints
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Ri tRivets
Old style connectors Permanent, Need field heating and head forming Safety issues Safety issues Tension on cooling is not estimated accurately Load distribution is not as good as that for bolts
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Ri tRivets
Old style connectors Permanent, Need field heating and head forming Safety issues Safety issues Tension on cooling is not estimated accurately Load distribution is not as good as that for bolts
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Pins Rarely used compared to bolts and welds Special projects only
Golden gate bridge approaches
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B ltBolts
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B ltBolts
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B lt Carbon Steel Bolts - Normal strength (A307)
Boltsg ( )
Similar to ordinary machine bolts Lower Strength, low load/shear connectors
High Strength Bolts - (A325 A325M A490 A490M etc ) High Strength Bolts - (A325, A325M, A490, A490M etc.) –Sec. 3, CISC Handbook
Heat treated for greater strength Higher shear resistance Higher shear resistance Can also be used in Friction Connections Can be used with or without washers
Bolt function Bolt function Snug tight bolts (allow slippage) Pre-tensioned bolts (slip critical)
B th h th lti t t th
Steel Connections -Dr. Seshu Adluri
Both have the same ultimate strength
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M t i l b h iMaterial behaviour
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M t i l b h iMaterial behaviour
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B ltBolts
Snug tight bolts (allow slippage) Easy to install (till about the first impact using the
pneumatic wrench). No inspection for tensionpneumatic wrench). No inspection for tension 10-20% of tension strength
Pre-tensioned bolts (slip critical –no slip)C tl t i t ll d i ti Costly to install, need inspection
Repeated loadings, bridges, communication towers, load reversals, impact, cranes, direct tension, etc.
Safety against twist-off, all bolts yield Both have the same ultimate strength
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P t i d B ltPre-tensioned Bolts
Installation Turn of the nut method (Table 8 –CSA-S16)
1/3 turn for Lb < 4db
1/2 turn for 4db < Lb < 8db (or 200 mm) 2/3 turn for longer bolts 2/3 turn for longer bolts
Tension indicator washers (ASTM F959) Cl. 23.8.3 Torque wrench Strain gauges, etc. Bolt tension as per Table 7, CSA-S16
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P t i ff tPretension effect
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P t i ff tPretension effect
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T i t ll d b ltTension controlled bolts
Wrench grips both the nut & bolt When required torch reached,
End twists off A plunger inside discharges the splined end
Ease of installation & consistency Ease of installation & consistency
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B lt di iBolt dimensions Standard dimensions, thread ,
lengths, bolt lengths for different grips Handbook p.6-152 to 6-156 Gauge dist. P.6-162
Nominal Bolt Size
Length Added To GripTo Grip
5/8” 7/8”¾” 1”
7/8” 1 1/8”1” 1 ¼”
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B ltBolts
Tension indicator washers
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T i i di t W hTension indicator Washers ASTM F959 washers (Cl. 23.8.3)
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Tension indicatorTension indicator Washers Washer with Washer with
Protrusions (Gap)
Protrusions fl tt B ltflatten as Bolt is tightened
Visually inspected to pensure that protrusions are flat (gap closed))
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Tension indicatorTension indicator Washers
Load Indicator Washers with a Visible Dye that squirts out when the
h h ffi i tlwasher has sufficiently flattened
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Pre-tension effect on shear forcePre tension effect on shear force on the joint
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L d El tiLoad vs. Elongation
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P t i ff tPre-tension effect
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Pre-tension effect on tension force on the jointthe joint
As the applied tension on the joint increases, the bolt elongates a little and eventually elongates enough (to the length before g ( gtightening. At that point, the bolt pretension effect disappears and the joint will behave as if the pretension had never been there. pIf the joint is unloaded at that point, the clamping effect due to pretension will return.
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B lt BIBLE!Bolts BIBLE! “Guide to Design Criteria for Bolted and Riveted Joints” by
Geoffrey L. Kulak, John W. Fisher & John H. A. Struik at:
http://www boltcouncil org/files/2ndEditionGuide pdf http://www.boltcouncil.org/files/2ndEditionGuide.pdf
RCSC: Research Council on Structural Connections Specification for Structural Joints Using ASTM A325 or A490 Bolts Specification for Structural Joints Using ASTM A325 or A490 Bolts
http://www.boltcouncil.org/index.html
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B l H dBolt Heads
Required MarkingsMarkings
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TypicalTypical Bolted J i tJoints
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Typical Bolted JointsTypical Bolted Joints
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Typical Bolted JointsTypical Bolted Joints
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Typical BoltedTypical Bolted Joints
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Typical Bolted Joints
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B i t b lt i ShBearing type bolts in Shear
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Bearing type Bolted JointsBearing type Bolted Joints
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B lt i ShBolts in Shear
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B lt b i ff tBolt bearing effect
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B lt i t i f ilBolts in tension failure
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B lt bl k t t ff tBolt block tear out effect
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Sh l ff tShear lag effect
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D i f b lt Cl 13 12Design for bolts Cl. 13.12 Shear: Vr = 0.6φb n m AbFu bolt >Vf, φb =0.8Shear: Vr 0.6φb n m AbFu-bolt Vf, φb 0.8
(Cl. 13.12.1.2)
Bearing: Br = 3φbr tdb n Fu-plate >Vf, φbr =0.8(Cl 13 12 1 2)(Cl. 13.12.1.2)
Tension: Tr = 0.75φb AbFu-bolt >Tf, φb =0.8(Cl. 13.12.1.3)
Slip resistance (Cl. 13.12.2.2): Vs = 0.53 c1 Ks mn AbFu-bolt >V (table 3 –CSA-S16)
Combined: 122
≤
+
r
f
r
f
TT
VV 1.9 1
s b u
V TV nA F
+ ≤
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Design for bolts Spacing etcDesign for bolts, Spacing, etc. If threads are intercepted in shear, reduce A to 70%If threads are intercepted in shear, reduce A to 70% spacing: 2.7db (usually 3db) Cl. 22.3.1 Min. Edge dist.: Table 6 (based on db & edge type) Max. Edge dist.: 12t or 150mm End distance: Table 6 or 1.5 db
Bolt hole diam.: db + 2mm (or 1/16”) Eff. hole diam.: hole diam.+2mm (for punched holes) d =d +4 mm (punched holes); d =d +2mm (drilled holes) dh=db+4 mm (punched holes); dh=db +2mm (drilled holes) Installation and inspection: Cl. 23, Washers: Cl. 23.5
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Bolt Power!It’s cheesy cartoon time!cartoon time!
She has the hex boltpower! He has the other kind!
Steel Connections -Dr. Seshu Adluri
power! He has the other kind!
Together, bolt and nut can keep the structure intact!
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E t i b lt d tiEccentric bolted connectionL = Moment/Load
b P8 1
b
b
P
Equivalent
7
6
2
3b
Equivalent eccentric load
6
5
3
4
D
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E t i b lt d tiEccentric bolted connection
Rotation effect only Direct shear effect only
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E t i b lt d tiEccentric bolted connection
Steel Connections -Dr. Seshu Adluri
Resultant of both rotation and direct shear effects
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B lt P i tiBolts – Prying action
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B lt P i tiBolts – Prying action
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Prying effectPrying effect
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B lt P i tiBolts – Prying action
Use procedure in the Handbook (no code clauses))
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Bolts –Bolts –Prying action
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WeldsWelds
MIG (Metal Inert Gas) welding
Steel Connections -Dr. Seshu AdluriFlux core welding
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WeldsWelds
Stick welding torch (tig)(Tungsten Inert Gas) welding
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Automated Weldingg
Plasma Welding & Cutting
Tungsten Inert Gas Arc Welding (TIG)
Steel Connections -Dr. Seshu Adlurilaser welding wire feed system
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W ldWelds
Weld failure underWeld failure under electron microscope
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Types of ypwelds
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Fillet welds
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Fillet welds
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B tt W ldButt Welds
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W ldi b lWelding symbols
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W ldi b lWelding symbols
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W ldi b lWelding symbols
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W ldi b lWelding symbols
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D i f W ld Cl 13 13Design of Welds Cl. 13.13Groove Welds φ 0 67Groove Welds φw =0.67 Base metal: Vr = 0.67φw Am Fu Weld metal: Vr = 0.67φw Aw Xu
Fillet Welds φw =0.67 Base metal: Vr = 0.67φw Am Fu Base metal: Vr 0.67φw Am Fu Weld metal: Vr = 0.67φw Aw Xu (1+0.5sin1.5θ)Mw
governs if θ > 45o for 350W
Flare bevel weld in OWSJ: Vr = 0.67φw Aw Fu Aw = 0.5 wfL
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W ld i tWeld sizes, etcGroove WeldsGroove Welds Min. groove depths for different situations applicable
Fillet WeldsFillet Welds Max. size: Dmax = t-2 mm t > 6mm
Dmax = t t ≤ 6mm Dmax = 0.75t for the rounded edges of rolled
tisections Min. size: Dmin = 5 mm tmax ≤ 12mm
Dmin = 6 mm 12mm ≤ tmax ≤ 20mmDmin = 8 mm 20mm ≤ tmaxmin max
Min length Lmin = max (4D, 40 mm) Lap Joints: min. lap length Llap = 5tmin or 25 mm
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P bl i W ld lProblems in Weld placement
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P bl i W ld lProblems in Weld placement
Alignment not very good
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ProblemsProblems in Weld
lplacement
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R fReferences Many pictures in this file are taken from various sources such as CISC, AISC, etc. The copyrights for those materials are with the original
sources. No copyright is claimed or implied by Dr. Seshu Adluri for things that are already under copyright protection. This file is for teaching purposes olny.
Steel Connections -Dr. Seshu Adluri