Experimental Study On Seismic Behaviors Of Dovetail Mortise-tenon Joints Of Ancient Timber Buildings

Due to its non-renewable characteristics, the protection of ancient buildings is very important. C hinese ancient buildings were mainly built with wood, which conists of many mortise-tenon joints without using any nails or iron. The mortise-tenon joint is one of the main features of ancient timber buildings. Under seismic action, the squeezed formation and friction between mortise and tenon could dissipate the energy. The destruction of the joints usually causes serious damage of the structure such as tilt and even collapse, so the study of seismic behaviors is significant for the seismic assessment and maintenance of ancient timber buildings.The dovetail mortise-tenon joint was selected as a research object which was widely used in ancient timber buildings. The unique load-transferring mechanism and seismic characteristics have been studied by model tests, theoretical analysis and numerical simulation. The main research contents are as follows:(1) Several common mortise-tenons were summarized. The load-transferring mechanism and usual failure forms of straight mortise-tenon and dovetail mortise-tenon were analyzed. Based on the actual performance of mortise-tenon of existing ancient timber buildings under seismic action, the necessity and importance was illustrated for the study of mortise-tenon joints.(2) In order to investigate the seismic performance of the mortise-tenon joints, considering the influences of vertical load, Pubofang, sparrow brace and size effect, the low-cyclic reversed loading tests were carried out. Seven mortise-tenon joints were made as the Fabrications Methods of Song Dynasty. The seismic behaviors and changing laws, such as failure characteristics, hysteretic behaviors, bearing capacity, degeneration of stiffness and energy diss ipation, were compared and analyzed(3) In order to investigate the influence of damage on the seismic performance of dovetail mortise-tenon joints, two common damage states-fungi and termites were simulated artificially. According to the low-cyclic reversed loading tests, the seismic behaviors, such as failure characteristics, hysteretic curve, skeleton curve, degeneration of stiffness and energy dissipation, were compared and analyzed.(4) The force mechanism of dovetail mortise-tenon joint was investigated and the moment-rotation relationship was deduced according to the mechanical equilibrium and deformation coordination. A two- linear model which defined with yield point and ultimate point was proposed based on the results of low-cyclic reversed loading test. Existed test approved that the formula is accurate and the calculated result agrees well with test result. According to the moment-rotation calculation formula, the factors affecting the rotational stiffness of dovetail joints were analyzed(5) Three different kinds of dovetail mortise-tenon joints were analyzed according to the analysis software ABAQUS. The load-transferring mechanism and failure patterns were verified through the deformation, stress distribution and moment-corner skeleton curves under low-cyclic reversed load. The results show that the finite element models could reflect the seismic behaviors of dovetail mortise-tenon joints of ancient timber buildings.