Effects of gaps on the seismic performance of traditional timber frames with straight mortise-tenon joint: Experimental tests, energy dissipation mechanism and hysteretic model

Abstract

The gaps are very common in the mortise-tenon (M-T) joints of the column-frame layer for the existing ancient timber buildings, which severely threaten the whole stability and safety of the structures. To study the effects of gaps on the seismic performance of traditional timber frames with straight M-T joint. Three 1/3.2-scaled straight M-T jointed timber frames, including one intact timber frame as a contrast and two timber frames with different gaps, were fabricated using Pinus sylvestris logs, and subjected them to reversed cyclic loading tests in strict accordance with the international test standard ISO-16670. The failure modes, load-displacement hysteretic response, strength, initial elastic stiffness, ductility, and stiffness degradation of the specimens were analyzed. The energy dissipation mechanisms of the timber frames with different gaps were evaluated, based on the law of energy conservation. Results indicated that the strength, initial elastic stiffness, and hysteretic energy dissipation capacity of the timber frames with gaps decreased significantly with increasing damaged degree. The gap can weaken the ductility of the timber frame, however, the inter-story drift ratio of the timber frame with gap can reached 0.16, indicating good deformation capacity. The gap had little effect on the degradation degree of the residual stiffness of the timber frame under large displacement amplitude. When the damage degree was 10%, under large displacement amplitude, the hysteretic energy consumption, elastic strain energy, and gravitational potential energy of the timber frame approximately accounted for 54%, 16%, and 30% of the total input energy, respectively. Based on the experimental results, the empirical formulas related to key cyclic performance parameters, considering the gap effects, were established. Based on the empirical relationships of the key hysteretic parameters of the timber frame with gaps, an improved hysteretic model for a timber frame with a gap was proposed and also validated. Good agreement between the model predictions and experimental results was observed.