Active Shear Planes of Bolted Connections Failing in Block Shear

Abstract

In the steel design codes worldwide, the shear area for calculating the block shear capacity of a bolted connection is either the gross or the net shear area. The authors have previously noted independent experimental evidence indicating the shear failure planes to lie midway between the gross and the net shear planes, termed the active shear planes. This paper presents the nonlinear contact finite brick element analysis results that confirm the location of the active shear planes, indicated by regions of maximum shear stresses. The finite-element analysis also found that shear stresses approach zero toward the free downstream end of the connection block. The veracity of the active shear area is further demonstrated in terms of the ability of the resulting block shear equation to predict the governing failure modes of test specimens consistently, in comparison with the equations assuming the gross and the net shear areas. Abstract: In the steel design codes worldwide, the shear area for calculating the block shear capacity of a bolted connection is either the gross or the net shear area. The authors have previously noted independent experimental evidence indicating the shear failure planes to lie midway between the gross and the net shear planes, termed the active shear planes. This paper presents the nonlinear contact finite brick element analysis results that confirm the location of the active shear planes, indicated by regions of maximum shear stresses. The finite-element analysis also found that shear stresses approach zero toward the free downstream end of the connection block. The veracity of the active shear area is further demonstrated in terms of the ability of the resulting block shear equation to predict the governing failure modes of test specimens consistently, in comparison with the equations assuming the gross and the net shear areas.

Block shear failure planes of bolted connections — Direct experimental verifications

“…In any case, Clements & Teh [9] have pointed out that the approach of using the net shear area A nv ignores the fact that the planes coinciding with the centrelines of the bolt holes in the direction of loading do not have maximum shear stresses due to the bolt bearing condition.…”

“…Although the finite element analysis results of Clements & Teh [9] clearly showed the location of the active shear planes, there has been no direct experimental verification supporting the use of the active shear planes. Comparisons among the gross, net and active shear planes against laboratory test results were carried out in the context of block shear failures that invariably involved both tensile and shear resistance components [1,9].…”

“…In a recent paper, Clements & Teh [9] have argued that, whether it is shear yielding or shear rupture, the critical shear planes lie midway between the gross and the net shear planes, as indicated by the results of nonlinear contact finite element analysis. These shear planes, depicted in Figure 2 and denoted A av , are termed the active shear planes [1,9] to distinguish them from the gross and net shear planes.…”

“…Comparisons among the gross, net and active shear planes against laboratory test results were carried out in the context of block shear failures that invariably involved both tensile and shear resistance components [1,9]. A more convincing case will result if the comparisons are made against laboratory test specimens each of whose ultimate load depends on the shear resistance only.…”

“…These shear planes, depicted in Figure 2 and denoted A av , are termed the active shear planes [1,9] to distinguish them from the gross and net shear planes. In Figure 2, the variable n r is the number of bolt rows, d h is the bolt hole diameter, and t is the plate thickness.…”