Tomoaki Soma

Study of mechanical properties of wooden bolt-nut connector I: effect of size and shape of thread on withdrawal strength

The withdrawal strength of a bolt-nut connector made from wood-based material was evaluated. The thread strength of the wooden bolt-nut connector was tested to select various parameters of the connector and the type of wood material; the wood materials tested were hard maple, white oak, ebony, glue-laminated bamboo, and densified Japanese cedar. A plane model of wooden threads with various thread angles was also evaluated. The results showed that the maximum failure load of the thread increased with increasing bolt density and connection area, which was calculated from the diameter of the bolt and the thickness of the nut. The withdrawal resistance after reaching the maximum load underwent a graded decrease because the bolt threads were broken one by one. In addition, the thread strength depended on the thread angle. In the model with a thread angle of 90°, compressive deformation in the transverse direction occurred prior to shear deformation along the root of the threads; the model with this thread angle thus had higher strength than those with other angles.

Pull-out Resistance Mechanism of Wari-kusabi Joints

Wari-kusabi Joints (Japanese traditional mortise-tenon joints with wedges) have been used as wooden structure joints in Japan. The pull-out resistance mechanism of the joint which connects post to beam was analyzed and modeled based on mechanical theory. The load-deformation curves in pull-out tests of mortise-tenon joints were influenced by resistance of compressive strain inclined to the grain and friction between post and beam. We proposed a mechanical model including these factors. The load-deformation curves in the elastic and plastic region could be estimated ; initial stiffness K, and yield point deformation δy were calculated by proposed design formula.