Steel Connections

Steel Connections Design Issues

Dr. Seshu Adluri

I Introduction d i  Steel

Connections

Unlike

concrete, connections in steel structures need special p design g Bolts, Rivets and Welds are typical connectors

Steel Connections -Dr. Seshu Adluri

J i i St Joining Structural t l elements l t Mechanical fastenings  Mechanically formed joints  Welding  Adhesive Adh i b bonding di 

Steel Connections -Dr. Seshu Adluri

MECHANICAL FASTENINGS        

Rivets B lti Bolting Stud Welding Powder-Actuated Fastenings Threaded Fasteners & Nails Expansion p Bolts Adhesive-held fasteners Mechanically formed joints

Steel Connections -Dr. Seshu Adluri

Ri t Rivets

    

Old style connectors Permanent, Need field heating and head forming Safety issues Tension on cooling is not estimated accurately Load distribution is not as good as that for bolts

Steel Connections -Dr. Seshu Adluri

Ri t Rivets

    

Old style connectors Permanent, Need field heating and head forming Safety issues Tension on cooling is not estimated accurately Load distribution is not as good as that for bolts

Steel Connections -Dr. Seshu Adluri

Pins  

Rarely used compared to bolts and welds Special projects only

Golden gate bridge approaches

Steel Connections -Dr. Seshu Adluri

B lt Bolts 

Steel Connections -Dr. Seshu Adluri

B lt Bolts 

Steel Connections -Dr. Seshu Adluri

B lt Bolts 

Carbon Steel Bolts -

Normal strength g ((A307))



Similar to ordinary machine bolts  Lower Strength, low load/shear connectors 

High Strength Bolts - (A325, (A325 A325M A325M, A490 A490, A490M etc etc.))    



–Sec. 3, CISC Handbook Heat treated for greater strength Higher shear resistance Can also be used in Friction Connections Can be used with or without washers

Bolt function 

Snug tight bolts (allow slippage)  Pre-tensioned bolts (slip critical)  Both B th h have th the same ultimate lti t strength t th Steel Connections -Dr. Seshu Adluri

M t i lb Material behaviour h i 

Steel Connections -Dr. Seshu Adluri

M t i lb Material behaviour h i 

Steel Connections -Dr. Seshu Adluri

B lt Bolts 

Snug tight bolts (allow slippage)  Easy

to install (till about the first impact using the pneumatic wrench). No inspection for tension  10-20% of tension strength 

Pre-tensioned bolts (slip critical –no slip)  Costly C tl tto install, i t ll need d iinspection ti  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

Steel Connections -Dr. Seshu Adluri

P t Pre-tensioned i dB Bolts lt 

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

 Tension

indicator washers (ASTM F959) Cl. 23.8.3  Torque wrench  Strain gauges, etc.  Bolt tension as per Table 7, CSA-S16

Steel Connections -Dr. Seshu Adluri

P t Pretension i effect ff t 

Steel Connections -Dr. Seshu Adluri

P t Pretension i effect ff t 

Steel Connections -Dr. Seshu Adluri

T Tension i controlled t ll d b bolts lt  

Wrench grips both the nut & bolt When required torch reached, 

End twists off  A plunger inside discharges the splined end 

Ease of installation & consistency

Steel Connections -Dr. Seshu Adluri

B lt di Bolt dimensions i 

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 Grip

5/8”

7/8”

¾”

1”

7/8”

1 1/8”

1”

1 ¼”

Steel Connections -Dr. Seshu Adluri

B lt Bolts 

Tension indicator washers

Steel Connections -Dr. Seshu Adluri

T Tension i iindicator di t W Washers h 

ASTM F959 washers (Cl. 23.8.3)

Steel Connections -Dr. Seshu Adluri

Tension indicator Washers 





Washer with Protrusions (Gap) Protrusions fl tt as Bolt flatten B lt is tightened Visually p to inspected ensure that protrusions are flat (gap closed))

Steel Connections -Dr. Seshu Adluri

Tension indicator Washers 

Load Indicator Washers with a Visible Dye that squirts out when the washer h h has sufficiently ffi i tl flattened

Steel Connections -Dr. Seshu Adluri

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

Steel Connections -Dr. Seshu Adluri

L d vs. El Load Elongation ti



Steel Connections -Dr. Seshu Adluri

P t Pre-tension i effect ff t 

Steel Connections -Dr. Seshu Adluri

Pre-tension effect on tension force on the joint 

As the applied tension on the joint increases, the bolt elongates a little and eventually elongates g ((to the length g before enough tightening. At that point, the bolt pretension effect disappears and the joint will behave as if the pretension had never been there. p If the joint is unloaded at that point, the clamping effect due to pretension will return.

Steel Connections -Dr. Seshu Adluri

B lt BIBLE! Bolts 

“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 

http://www.boltcouncil.org/index.html



Steel Connections -Dr. Seshu Adluri

B l H Bolt Heads d 

Required Markings

Steel Connections -Dr. Seshu Adluri

Typical Bolted J i t Joints 

Steel Connections -Dr. Seshu Adluri

Typical Bolted Joints



Steel Connections -Dr. Seshu Adluri

Typical Bolted Joints



Steel Connections -Dr. Seshu Adluri

Typical Bolted Joints



Steel Connections -Dr. Seshu Adluri

Typical Bolted Joints



Steel Connections -Dr. Seshu Adluri

B i ttype b Bearing bolts lt iin Sh Shear 

Steel Connections -Dr. Seshu Adluri

Bearing type Bolted Joints



Steel Connections -Dr. Seshu Adluri

B lt iin Sh Bolts Shear 

Steel Connections -Dr. Seshu Adluri

B lt b Bolt bearing i effect ff t 

Steel Connections -Dr. Seshu Adluri

B lt in Bolts i ttension i ffailure il 

Steel Connections -Dr. Seshu Adluri

B lt bl Bolt block k ttear outt effect ff t 

Steel Connections -Dr. Seshu Adluri

Sh Shear llag effect ff t 

Steel Connections -Dr. Seshu Adluri

D i ffor b Design bolts lt 

Shear:

Cl 13.12 Cl. 13 12

Vr = 0.6φb n m AbFu-bolt V f, u bolt >V

φb =0.8 0.8

Br = 3φbr tdb n Fu-plate

>Vf,

φbr =0.8

Tr = 0.75φb AbFu-bolt

>Tf,

φb =0.8

(Cl. 13.12.1.2)



Bearing: (Cl 13.12.1.2) (Cl. 13 12 1 2)



Tension: (Cl. 13.12.1.3)



Slip resistance (Cl. 13.12.2.2):  Vs = 0.53 c1 Ks mn AbFu-bolt >V

Combined:

Vf   Vr

2

2

  Tf   +   ≤ 1   Tr 

(table 3 –CSA-S16)

V T + 1.9 ≤1 Vs nAb Fu

Steel Connections -Dr. Seshu Adluri

Design for bolts bolts, Spacing Spacing, etc etc.         

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) dh=db+4 mm (punched holes); dh=db +2mm (drilled holes) Installation and inspection: Cl. 23, Washers: Cl. 23.5

Steel Connections -Dr. Seshu Adluri

It’s cheesy cartoon time!

Bolt Power!



She has the hex bolt power!

He has the other kind!

Together, bolt and nut can keep the structure intact! Steel Connections -Dr. Seshu Adluri

E Eccentric ti b bolted lt d connection ti L = Moment/Load

 8

1

b 7

2

6

3

5

4

P

b b

Equivalent eccentric load

D

Steel Connections -Dr. Seshu Adluri

E Eccentric ti b bolted lt d connection ti 

Rotation effect only

Direct shear effect only

Steel Connections -Dr. Seshu Adluri

E Eccentric ti b bolted lt d connection ti 

Resultant of both rotation and direct shear effects Steel Connections -Dr. Seshu Adluri

B lt – Prying Bolts P i action ti 

Steel Connections -Dr. Seshu Adluri

B lt – Prying Bolts P i action ti 

Steel Connections -Dr. Seshu Adluri

Prying effect 

Steel Connections -Dr. Seshu Adluri

B lt – Prying Bolts P i action ti 

Use procedure in the Handbook (no code clauses))

Steel Connections -Dr. Seshu Adluri

Bolts – Prying action



Steel Connections -Dr. Seshu Adluri

Welds  MIG (Metal Inert Gas) welding

Flux core welding

Steel Connections -Dr. Seshu Adluri

Welds  (Tungsten Inert Gas) welding

Stick welding torch (tig)

Steel Connections -Dr. Seshu Adluri

Automated Welding g  Plasma Welding & Cutting Tungsten Inert Gas Arc Welding (TIG)

laser welding wire feed system Steel Connections -Dr. Seshu Adluri

W ld Welds 

Weld failure under electron microscope

Steel Connections -Dr. Seshu Adluri

Types yp of welds 

Steel Connections -Dr. Seshu Adluri

Fillet welds 

Steel Connections -Dr. Seshu Adluri

Fillet welds 

Steel Connections -Dr. Seshu Adluri

B tt Welds Butt W ld 

Steel Connections -Dr. Seshu Adluri

W ldi symbols Welding b l 

Steel Connections -Dr. Seshu Adluri

W ldi symbols Welding b l 

Steel Connections -Dr. Seshu Adluri

W ldi symbols Welding b l 

Steel Connections -Dr. Seshu Adluri

W ldi symbols Welding b l 

Steel Connections -Dr. Seshu Adluri

D i off W Design Welds ld Groove Welds  Base metal:  Weld metal:

Cl 13.13 Cl. 13 13

φw =0.67 0 67 Vr = 0.67φw Am Fu Vr = 0.67φw Aw Xu

Fillet Welds φw =0.67  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

Steel Connections -Dr. Seshu Adluri

W ld sizes, Weld i etc t Groove Welds  Min. groove depths for different situations applicable Fillet Welds  Max. size:  

 

sections ti Min. size:

Dmax = t-2 mm Dmax = t Dmax = 0.75t

t > 6mm t ≤ 6mm for the rounded edges of rolled

Dmin = 5 mm tmax ≤ 12mm 12mm ≤ tmax ≤ 20mm Dmin = 6 mm 20mm ≤ tmax Dmin = 8 mm Min length Lmin = max (4D, 40 mm) Lap Joints: min. lap length Llap = 5tmin or 25 mm

Steel Connections -Dr. Seshu Adluri

P bl Problems iin W Weld ld placement l 

Steel Connections -Dr. Seshu Adluri

P bl Problems iin W Weld ld placement l 

Alignment not very good

Steel Connections -Dr. Seshu Adluri

Problems in Weld placement l



Steel Connections -Dr. Seshu Adluri

R f References 

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