Theoretical model of bending moment for the penetrated mortise-tenon joint involving gaps in traditional timber structure

Abstract

Mortise-tenon joints often have neighboring gaps due to initial manufacturing errors and accumulated damage over thousands of years. The looseness of joints can cause degradation of mechanical performance of joint, which might lead to the collapse or damage of the entire structure. In this study, the mechanical performances of penetrated mortise-tenon joint involving gaps were investigated. Working states and judging criteria for different working states were produced under positive and negative loading. A theoretical model of the bending moment for a loose mortise-tenon joint was proposed. Full-scale experiments were conducted to verify the proposed theoretical model. Transverse four-column wooden frames, characterizing the overall mechanical properties of a structure, were chosen to clarify the applicability of the proposed model. A simplified finite element model (FEM) with bar units and rotation springs was established and verified using solid FEM. The deformation characteristics and lateral resistance of wooden frame were then analyzed. The results showed that the theoretical model was in good agreement with test results and could be used to estimate the joint bending moment. Simplified models of joints were then applied in the establishment of a timber structure. The lateral behavior of the wood frame mainly contributed by column foot joints at the beginning of rotation and penetrated mortise-tenon joints at later rotation. This study provided important references on the protection and repair of existing traditional timber structures.