Mechanical behavior and degradation mechanism of mortise-tenon joints considering inclination damage in traditional timber buildings: theoretical model, numerical analysis, and experimental verification

Looseness-induced inclination damage can cause degradation of mechanical behavior of wooden mortise-tenon (M-T) joints. However, the degradation mechanism and evaluation method of mechanical behavior of inclined M-T joints remained unclear. To predict and evaluate the effect of inclination damage on the mechanical and hysteretic behavior of M-T joint, the embedded compression and friction mechanisms of inclined M-T joint were investigated and a simplified equation for predicting the moment-rotation relationship was established and validated by the cyclic loading test results of four 1/3.2-scaled M-T joints. The hysteretic model and parameters as well as degradation law of flexural behavior of these joints were determined, the numerical model for inclined joints was established using the OpenSees software. Results showed that the predictions of models were in good agreement with test results, demonstrating the proposed methods could be used to estimate the damaged joint's moment-resisting, rotational stiffness, hysteretic characteristics, and strength and stiffness degradation level. Increasing inclination degree would markedly reduce the joint's energy dissipation and flexural behaviors. At an inclined degree of 5%, the ultimate moment of inclined joint reduced up to 39%. This study would provide important references on the safety evaluation and accurate quantification of mechanical behavior of damaged M-T joints.