Pretension loss in bolted timber joint under external tensile load

The pretension force for bolted timber joints increases the frictional resistance between the clamping wood and steel plate. Increasing the frictional resistance improves joint stiffness and strength. External tensile load causes the pretension loss in bolted timber joints, but this mechanism remains unclear. This study investigated the mechanism of pretension-bolted timber joints with different pretension forces and clamping part lengths under external tensile loads. Nonlinear finite element analysis (FEA) was conducted. The FEA results were validated by comparison with the experimental results. The separation behavior and mechanism of the clamping wood were also investigated using the FEA results. Moreover, the applicability of conventional theoretical models of the load factor, which is an index for evaluating the pretension loss of bolts, to bolted timber joints was investigated for their practicality. The FEA results provided a good prediction of the initial stiffness, maximum strength, and load factor for the experimental results. The FEA results also showed that increasing the pretension force of the bolt and the length of the clamping wood delayed the onset of separation of the contact interface.