Effect of changes in the moisture content due to surrounding relative humidity on the contact stress in traditional mortise and tenon joints, 3: Pull-out strength of compressed sugi [Cryptomeria japonica wood] komisen joints

This research is focused on evaluating the efficiency and failure mechanism of joints using a komisen (Japanese traditional square key) of compressed sugi (Japanese ceder ; Cryptomeria japonica D. Don), and to evaluate to what extend hozo-komisen (Japanese traditional mortise and tenon) joint strength is being influenced by the recovery of compressed sugi komisen when exposed to long term humidity cycling. Compressed sugi komisen showed a change of yield and rupture mode compared to shirakashi (Quercus myrsinaefolia Blume) komisen, as did the komisen inserting direction into the joint because it has characteristic and anisotropic properties. The compressed sugi komisen joint (C1R) , when inserted according to the R-type, yielded by shear of the komisen and reached its maximum strength (Pmax : 12.5 kN) just before rupture at 10 mm displacement at the tenon. The failure mode showed a different pattern, compared to the shirakashi komisen joint (S1R) where the central komisen yielded in bending. The strength of the compressed sugi komisen joint (C1RH) exposed to cyclic changes of humidity (40-80%RH) during two years increased in maximum strength, yield strength, and energy absorption. This is in contrast to the shirakashi komisen joint (C1RH) that showed a dramatic and remarkable strength decrease when exposed to the climatic environment.