Qualitative Assessment of Failure in Bolted Connections: Tsai-Wu Criterion

In a companion paper, a characterization is presented of stress fields in a single-shear bolted connection subjected to tension loading. Numerous stress contours are presented that illustrate the magnitude of the parallel-to-grain compression and shear stresses, as well as the perpendicular-to-grain tension stresses. In addition, regions of potential failure in the selected specimens are identified based on a maximum stress failure criterion. The work presented in this paper represents additional efforts to identify the effect of stress interactions on the strength of the previously mentioned connections. The Tsai-Wu criterion, quantified by its failure index, is used as the tool to identify stress interactions between the aforementioned stress components. Connection geometries similar to those discussed in the companion paper [end distance/bolt diameter ( e ∕ d ) = 4 ; and length of bolt in main member/bolt diameter (aspect ratio) ( l ∕ d ) = 2 , 5 , and 7 ] are studied. In addition, several other geometries are discussed that illustrate the effects of changing aspect ratio and end distance. A number of significant findings are reached in this study. As is the case in the companion study, all connections with ( l ∕ d ) = 2 have nearly uniform distributions of the Tsai-Wu failure index (FI) through the specimen thickness. No significant pin bending is associated with this geometry. Connections with l ∕ d > 4 have a failure mode (interpreted from the numerical model) that includes substantial pin bending due to steel yielding, wood crushing, and localized cracking.