Effects of gaps on the rotational performance of traditional straight mortise-tenon joints

Abstract

Gaps are very common in the mortise-tenon (M-T) joints of traditional timber structures, and they significantly reduce the rotational performance of joints. To evaluate the effect of gaps on the rotational behavior of straight M-T joints, we fabricated four 1/3.2-scaled Chinese traditional straight M-T joint specimens using Pinus sylvestris logs, one without a gap and three with different gaps, and subjected them to cyclic loading tests strictly in accordance with the international test standard ISO-16670. The failure modes, strength, initial rotational stiffness, ductility, deformation, and energy dissipation capacity of the joints were investigated. The results indicated that the apparent slippage, the tenon pulled out, and the plastic deformation for the mortise edge were exhibited in the specimens with gaps. The bending moment, initial rotational stiffness, and energy dissipation capacity of the joints with gaps gradually decreased as the damaged degree increased. The ultimate rotation of joints with gaps reached 0.2 rad, indicating a good deformation capacity. Furthermore, the gap can aggravate the degree of stiffness degradation of the M-T joint at the same rotation. Based on the experimental results, the empirical degradation formulas related to key cyclic performance parameters, considering the gap effects, were established. Based on the degradation relationships of the key hysteretic parameters of the joint with gaps, a hysteretic model for a joint with a gap was proposed and validated. Good agreement between the model predictions and experimental results was observed.