Chapter 4 - Bolted Connections
The limit state of shear rupture is introduced in SCM J3.6 (SCM pg 16.1-125).
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 Pu and Pa are the LRFD and ASD factored loads, respectively, applied to the bolt. These forces are computed using the mechanics principles discussed in BGSCM 4.3.
In this case Rn is the nominal shear strength of a shear plane is computed using SCM equation J3-1:
Rn = FnvAb
The nominal shear strength of a connection that is concentrically loaded is determined by:
Rn = FnvAbns
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.
SCM 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 SCM 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 Ab, the SCM specification reduces Fnv. Use the tabulated value for Fnv 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 BGSCM 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.