Fracture Modeling of Bolted Connections in Wood and Composites

Abstract

Brittle failures are frequently encountered in wood bolted connections. Because of high localized stress concentrations, cracks initiate at the boundary of the bolt-hole and propagate parallel to the grain. This paper is intended to examine the attributes of fracture mechanics in predicting the brittle failure of such structural joints under short-term loading. Models proposed for wood and fiber-reinforced composites are reviewed. Then solution techniques for the stress analysis and failure criteria of connections are presented with typical examples from literature. It is found that several conditions must be considered simultaneously in the analysis. These are the geometric nonlinearity due to sliding contact, the material nonlinear behavior before and after fracture, and the fastener deformation in the plane parallel to the bolt axis in the case of connections between thick members. As yet, there is no failure theory for bolted joints in orthotropic materials with general applicability. Fracture mechanics models are more appropriate than strength criteria as tools for predicting brittle failures. They should, however, be applied with caution by identifying the fracture parameters that control the initiation and stable propagation of cracks until ultimate failure.