A Beginner's Guide to the Steel Construction Manual, 14th ed.

Chapter 4 - Bolted Connections

2006, 2007, 2008, 2011 T. Bartlett Quimby

Overview

Mechanics of Load Transfer

Finding Forces on Bolts

Hole Size and Bolt Spacing

Tensile Rupture

Shear Rupture

Slip Capacity

Chapter Summary

Example Problems

Homework Problems

References


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Section 4.8

Bolt Summary

Last Revised: 11/04/2014

Strength Limit States:

All strength limit states take the form:

LRFD ASD
Ru < ftRn Ra < Rn/Wt
Req'd Rn = Ru/ft < Rn Req'd Rn = Ra Wt < Rn
Ru / (ftRn< 1.00 Ra / (Rn/Wt) < 1.00

Which is:  FORCE on a bolt < STRENGTH of a bolt

The STRENGTH of a bolt is computed by:

Simple Tension or Shear

Limit State Specification Nominal Capacity Typical Design Variables f W
Tensile Rupture J3.6 Single Bolt Capacity:
FntAb
Bolt Material, Bolt Size 0.75 2.00
Shear Rupture J3.6 Single Shear Plane:
FnvAb
Bolt Material, Bolt Size 0.75 2.00
Slip Capacity J3.8 Single Shear Plane:
mDuhfTbns
Bolt Material, Bolt Size 1.00, 0.85, or 0.70 1.50, 1.76, or 2.14

Combined Shear and Tension:

Bearing Type Fasteners (-X or -N bolts)

  • Modify the nominal tensile rupture capacity for the presence of shear (SCM J3.7)
  • Apply the shear rupture limit state without modification
Limit State Specification Nominal Capacity, Rn Typical Design Variables f W
Tensile Rupture J3.7 Single Bolt Capacity:
F'ntAb
Bolt Material, Bolt Size 0.75 2.00
Shear Rupture J3.6 Single Shear Plane:
FnvAb
Bolt Material, Bolt Size 0.75 2.00

Slip Critical Type Fasteners (-SC bolts)

  • Modify the nominal slip capacity for the presence of tension (SCM J3.9)
  • Apply the tensile rupture limit state without modification
Limit State Specification Nominal Capacity, Rn Typical Design Variables f W
Tensile Rupture J3.6 Single Bolt Capacity:
FntAb
Bolt Material, Bolt Size 0.75 2.00
Slip Capacity J3.9 Single Shear Plane:
mDuhfTbnsks
Bolt Material, Bolt Size 1.00, 0.85, or 0.70 1.50, 1.76, or 2.14

The FORCE on a bolt is computed by:

Forces Concentric with the Bolt Group at the Faying Surface:

  • All bolts are assumed to be equally stressed in tension.
  • All shear planes are assumed to be equally stressed in shear.

Eccentricity in the Plane of the Faying Surface: 

  • Elastic Vector Method:  See SCM pg 7-8.  Computes shear in the bolts.  Direct method that is conservative and has an inconsistent factor of safety.
  • Instantaneous Center of Rotation Method:  See SCM pg 7-6.  Computes the relationship between the applied load and the shear load in the worst case bolt.  Iterative method that is more consistent with test results and not as conservative as the Elastic Method.

Eccentricity out of the Plane of the Faying Surface:

  • Case I Method:  See SCM pg 7-10.  Basic mechanics (Mc/I) using the compression contact area to find the tension in the worst case bolt.  Finding Ix may be iterative.  If the shear is concentric with the bolt group it is equally divided among the shear planes otherwise use either the elastic vector or IC method to find the bolt shear forces.
  • Case II Method:  See SCM pg 7-12.  Uses basic statics (Applied Moment = Pe = rat n' dm= Internal Moment) without considering the contact area to find the tension in the worst case bolt. If the shear is concentric with the bolt group it is equally divided among the shear planes otherwise use either the elastic vector or IC method to find the bolt shear forces.

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