The inclination damage, caused by the looseness to mortise and tenon (M&T) joints, seriously threatens the safety and stability of the existing historic multi-story timber buildings and increases the risk of structural collapse. To investigate the influence of the tilt damage caused by joint looseness on the seismic behavior of historic timber frame, an intact timber frame and two tilted timber frames, with a scale of 1/3.2 and straight M&T connection, were fabricated and subjected to the cyclic loading tests. The failure modes, hysteresis characteristics, lateral load-carrying capacity, initial lateral stiffness, ductility, and energy dissipation behavior of the specimens were investigated. The experimental results indicated that compared with the intact timber frame, the tilt damage made the compression plastic deformation of the mortise edge more obvious, the tenon’s split and pull-out were more severe. The hysteresis curves of the tilted timber frames exhibited apparent horizontal slippage at the negative initial loading. At a tilt degree of 4.28%, the negative lateral load-bearing capacity, negative initial lateral stiffness, and accumulative hysteresis energy dissipation of the tilted timber frame degraded to 33%, 42%, and 51% of those of the intact timber frame, respectively. The joint looseness-induced inclination damage can decrease the ductility of the timber frame during the negative loading. Furthermore, the empirical expressions of the key hysteretic parameters were established according to the test results. Based on the degeneration relationship of the critical hysteresis parameters and hysteretic rules, a novel and improved bilinear slip hysteretic model for the tilted timber frame, considering the inclination damage during the service, pinching, negative slipping, and degradation of hysteretic characteristics, was developed and verified by the test results. Good agreements between the predictions and test results were observed.
Xie et al. (Fri,) studied this question.