A Beginner's Guide to the Steel Construction Manual, 13^th ed. (old)

Chapter 4 - Bolted Connections

© 2006, 2007, 2008 T. Bartlett Quimby

Section 4.6

Shear Rupture

The limit state of shear rupture is introduced in the specification in section J3.6 (SCM pg 16.1-108).

The Limit State:

The basic limit state follows the standard form.  The statement of the limit states and the associated reduction factor and factor of safety are given here:

The values of P_u and P_a are the LRFD and ASD factored loads, respectively, applied to the bolt. These forces are computed using the mechanics principles discussed in Sections 4.3.

In this case R_n is the nominal shear strength of a shear plane is computed using SCM equation J3-1:

R_n = F_nvA_b

Where:

• F_nv is obtained from SCM Table J3.2 (SCM pg 16.1-104)
• A_b is the nominal cross sectional area of the bolt (pd_b²/4), ignoring threads.

[2010 Spec note:  Table J3.2 has been modified to increase F_nv values in the 2010 Specification. Bolt groups have also been created with each group containing a set of different ASTM types of bolts.]

The nominal shear strength of a connection that is concentrically loaded is determined by:

R_n = F_nvA_bn_s

Where:

• n_s is the number of shear planes that transfer the complete load.

For connections that are not concentrically loaded the shear force in the worst case shear plane is determined by structural mechanics and compared against the capacity of a single shear plane.

Table J3.2 tabulates nominal shear stresses for the commonly used structural bolts.  It also provides provision for computing the nominal shear stress for other types of threaded fasteners.

You will notice that Table J3.2 has rows for conditions including or excluding threads from the shear planes.  If threads exist in a shear plane then there is less area available to transfer the shear.  Instead of computing a reduced A_b, the SCM specification reduces F_nv instead.  Use the tabulated value for F_nv that applies to your design situation.

Combined Tension and Shear in Bearing-Type Connections

When this condition occurs, the tensile capacity is reduced as discussed in Section 4.5.

Sample Spreadsheet Computation

This spreadsheet computes both the shear and tension strength limit states, including combined shear and tension.  The input consists of information about the bolts (type, size, tabulated stress, number) and loads (shear and tension) obtained previous to doing this calculation.

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