Behavior of traditional Chinese mortise-tenon joints: Experimental and numerical insight for coupled vertical and reversed cyclic horizontal loads

Mortise-tenon joints in traditional Chinese architecture are of major importance. Studying their performance under horizontal loads loads is paramount for China, where there are more than ten thousand historical pavilions and buildings -some of them 1000 years old-built with such a technology and where seismicity is high. To probe the impact of damage to mortise-tenon joints on the seismic performance of unidirectional straight-tenon wooden frames, this paper uses the so-called artificial damage simulation method. Under the condition of considering damage depth and degree of surface damage of the tenon, one intact wooden frame and 3 mortise-tenon wooden frames (having joints with different decay degrees of damage) are built in the laboratory using a 1:3.52 scale ratio. To obtain failure modes and hysteresis performance of the specimens, low-cycle reciprocating loading tests were conducted. This paper compares and analyzes the characteristics of edge point strain change of tenon and socket joints, the variation law of seismic performance such as hysteresis characteristics of the wood frame, the stiffness degradation and energy dissipation ability, and the accumulation of damage during repeated loading of the wood frame. Results show that, with an increase of the degree of decadent damage, the peak of the hysteresis curve of the wood frame decreases gradually, the tendency of the skeleton curve is flattened, the equivalent viscous damping coefficient decreases, and the seismic behavior of the wood frame drops. A sophisticated FE approach with contact-frictional interfaces at the mortise-tenon joints and with beams exhibiting a non-linear behavior is adopted to fit data obtained experimentally in the lab. A satisfactory agreement is found between numerical simulations and experimental results, with the comparison giving interesting insight into the expected behavior of such connections in case of an earthquake.