Fracture modeling of bolted connections in wood and composites

Brittle failures are frequently encountered in wood bolted connections. Bec ause of high localized stress concentrations, cracks initiate at the bounda ry of the bolt-hole and propagate parallel to the grain. This paper is inte nded to examine the attributes of fracture mechanics in predicting the brit tle failure of such structural joints under short-term loading. Models prop osed for wood and fiber-reinforced composites are reviewed. Then solution t echniques for the stress analysis and failure criteria of connections are p resented with typical examples from literature. It is found that several co nditions must be considered simultaneously in the analysis. These-are the g eometric nonlinearity due to sliding contact, the material nonlinear behavi or before and after fracture, and the fastener deformation in the plane par allel 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 shou ld, however, be applied with caution by identifying the fracture parameters that control the initiation and stable propagation of cracks until ultimat e failure.