Effective Shear Plane Model for Tearout and Block Shear Failure of Bolted Connections

Abstract

In spite of many revisions to the block shear requirements of the AISC Specification, the model in the current Specification can result in calculated strengths and failure modes that are inconsistent with published test data. The inconsistencies are primarily related to the assumed interaction of tensile and shear resisting mechanisms, combined with the definition of net and gross shear planes that are unrealistic. Using recently published test results of single-bolt connections in mild and high-strength steel plates, the shear failure planes are observed to be neither the assumed net nor gross shear planes, which are the basis of the current design provision, but rather effective shear planes with a calculated area that is between the net and gross areas. Based on the tensile rupture and shear yielding mechanism, and assuming that the steel on the effective shear planes is fully strain hardened, a simpler and more accurate block shear design equation is proposed. The new equation is straightforward to implement as it requires a simple rearrangement of existing design variables to determine an effective shear failure area. Through verifications against 161 gusset plate specimens, tested by independent researchers around the world, the proposed equation is shown to be significantly more accurate than the current AISC, Canadian, European and Japanese block shear design provisions. A resistance factor of 0.85 is recommended for use with the proposed equation, based on the available statistics from tests and well-established LRFD reliability principles. An example is presented to illustrate the impact of the proposed design provision, which can result in significantly fewer bolts per connection and/or smaller gusset plates, leading to simpler and more economical designs.