Hysteretic Behavior Characterization of Mortise and Tenon Joints Reinforced Using Viscoelastic Dampers in Historic Timber Frames

Viscoelastic damper (VED) reinforcement has been successfully implemented in Chuan-dou–type timber buildings in southwest China, a region with high seismic intensity. However, the development of analysis models for this reinforcement technique trails behind the requirements of engineering practice. In this study, experimental observations of quasi-static test results for mortise-tenon joints were investigated. The results show that mortise-tenon joints exhibit damage gaps under cyclic loading. Motivated by these observations, the geometric equations for the height of the embedded compression area were derived by considering the damage gap and the tenon’s construction forms. Equivalent stiffness and damping theories were applied to the physical conditions to describe the mechanical properties of VEDs. In the equilibrium equations, external loads were equilibrated by a combination of elastic force provided by a VED and interaction force between the tenon and mortise. Through linearizing the nonlinear segmented skeleton curve model, the new linearization model improves computational efficiency by requiring solution of only the key control points in the nonlinear model. A typical loading and unloading rule is proposed here, and a computational procedure for the proposed hysteresis model is presented in detail. By comparing the existing reinforcement test results for mortise-tenon joints with four construction forms, the proposed model is capable of predicting the hysteresis behaviors of these joints with reasonable accuracy. Further validation was conducted with a focus on the hysteretic behaviors of two Chuan-dou–type timber frames.