Experimental Study on Seismic Performance of Through-Tenon Joints with Different Degrees of Looseness

This study investigated the impact of joint looseness on the seismic performance of through-tenon joints in traditional timber structures. The through-tenon joint from the fourth floor of Guangyue Tower served as the research prototype. Five specimens, including one intact joint and four joints with varying looseness levels, were fabricated at a geometric scaling ratio of 1:2. Low-cycle reversed cyclic loading tests were conducted to characterize the mechanical behaviors of all specimens. Evaluation parameters included failure modes, moment–rotation hysteretic curves, skeleton curves, strength degradation curves, stiffness degradation curves, energy dissipation capacity, and ductility performance. The test results revealed that increasing joint looseness transformed the hysteretic curve from an anti-Z shape to an arch shape. This transformation involved aggravated pinching behaviour and evident slippage. All test specimens showed strength degradation coefficients below unity. Loosened joints exhibited lower stiffness and energy dissipation capacity than the intact joint. These properties declined monotonically with increasing looseness levels. Ductility performance revealed a remarkable directional discrepancy under bidirectional loading. Deformation responses diverged notably under positive and negative cyclic loads. All specimens possessed favorable global deformability. Ultimate rotation angles and loading displacements correlated positively with the degree of looseness. Tenon withdrawal deformation continuously accumulated with an increasing rotation angle.