Steel Connections Design Issues - Faculty ofadluri/courses/steel/ppt files1/Topic...

Steel ConnectionsDesign Issues

Dr. Seshu Adluri

I d iIntroduction

Steel ConnectionsUnlike concrete, connections in

steel structures need special designp gBolts, Rivets and Welds are typical

connectorsconnectors

Steel Connections -Dr. Seshu Adluri

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

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

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

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

Pins Rarely used compared to bolts and welds Special projects only

Golden gate bridge approaches

B ltBolts

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

Both have the same ultimate strength

M t i l b h iMaterial behaviour

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

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

P t i ff tPretension effect

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

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”

B ltBolts

Tension indicator washers

T i i di t W hTension indicator Washers ASTM F959 washers (Cl. 23.8.3)

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))

Tension indicatorTension indicator Washers

Load Indicator Washers with a Visible Dye that squirts out when the

h h ffi i tlwasher has sufficiently flattened

Pre-tension effect on shear forcePre tension effect on shear force on the joint

L d El tiLoad vs. Elongation

P t i ff tPre-tension effect

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.

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

B l H dBolt Heads

Required MarkingsMarkings

TypicalTypical Bolted J i tJoints

Typical Bolted JointsTypical Bolted Joints

Typical BoltedTypical Bolted Joints

Typical Bolted Joints

B i t b lt i ShBearing type bolts in Shear

Bearing type Bolted JointsBearing type Bolted Joints

B lt i ShBolts in Shear

B lt b i ff tBolt bearing effect

B lt i t i f ilBolts in tension failure

B lt bl k t t ff tBolt block tear out effect

Sh l ff tShear lag effect

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

VV 1.9 1

V TV nA F

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

Bolt Power!It’s cheesy cartoon time!cartoon time!

She has the hex boltpower! He has the other kind!

power! He has the other kind!

Together, bolt and nut can keep the structure intact!

E t i b lt d tiEccentric bolted connectionL = Moment/Load

b P8 1

Equivalent

Equivalent eccentric load

E t i b lt d tiEccentric bolted connection

Rotation effect only Direct shear effect only

E t i b lt d tiEccentric bolted connection

Resultant of both rotation and direct shear effects

B lt P i tiBolts – Prying action

Prying effectPrying effect

Use procedure in the Handbook (no code clauses))

Bolts –Bolts –Prying action

WeldsWelds

MIG (Metal Inert Gas) welding

Steel Connections -Dr. Seshu AdluriFlux core welding

WeldsWelds

Stick welding torch (tig)(Tungsten Inert Gas) welding

Automated Weldingg

Plasma Welding & Cutting

Tungsten Inert Gas Arc Welding (TIG)

Steel Connections -Dr. Seshu Adlurilaser welding wire feed system

W ldWelds

Weld failure underWeld failure under electron microscope

Types of ypwelds

Fillet welds

B tt W ldButt Welds

W ldi b lWelding symbols

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

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

P bl i W ld lProblems in Weld placement

Alignment not very good

ProblemsProblems in Weld

lplacement

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 Design Issues - Faculty ofadluri/courses/steel/ppt files1/Topic...

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