Rotational Performance of Traditional Straight Mortise-Tenon Joints with Gap: Theoretical Model and Numerical Analyses

Gaps are very common in the mortise-tenon (M-T) joints of traditional timber structures. To investigate the rotational behavior of straight M-T joints with gaps, the mechanical mechanism and contact states between the mortise and tenon for the straight M-T joints with gaps were analyzed. A moment-rotation theoretical model of straight M-T joint with gap, based on the embedded compressive and friction mechanisms of the contact surfaces, was proposed and verified by the cyclic loading tests of four 1/3.2-scaled straight M-T joint specimens with different gaps. To further predict the deformation modes and hysteretic behavior of the joint involving gap, nonlinear numerical analyses were performed using ABAQUS. Results indicated that the predictions of theoretical and numerical model were in good accordance with the experimental results. Then, the parametric analyses were carried out based on the validated finite element model, the effects on the rotational behavior of straight M-T joint of major parameters, such as the friction coefficient of wood, vertical gaps, and horizontal gaps, were analyzed. It is found that the initial rotational stiffness, yielding moment, peak moment, and ductility of the joint with gap increased with an increase in the friction coefficient. The initial rotational stiffness, yielding moment, and peak moment of the joint remarkably decreased with the increase of the vertical and horizontal gap. The ductility of joint significantly reduced with the increasing vertical gap, however, the joint slightly improved with an increase in the horizontal gap.