Experimental Study On Seismic Behavior Of Dovetail Mortise-tenon Joints Under Different Loose Degrees In Ancient Timber Buildings

Ancient timber buildings are the wisdom which handed down by Chinese ancestor for thousands of years, it has important scientific, cultural and artistic quality. Whereby, it is an important feature that the members of ancient timber structure connected by mortise-tenon joints. Mortise-tenon joint has advantages of good energy dissipation and deformation capacity, while the mortise-tenon joints occurred different loose degrees under the internal and external environment after hundreds or even thousands of years. As a result, mastering the seismic behavior of mortise-tenon joints is the foundation of repairing and protecting the ancient wood structure. The main research work this paper accomplished is as follows:Through adopted the method of artificial simulation of looseness, considering the influence of different loose degrees, the behaviors of joints such as the failure modes, moment-corner hysteretic loops, skeleton curves, degradation of stiffness and strength, energy dissipation and deformation capacity were studied through low-cycle reversed loading experiment. The results indicate that the tenons are partially pulled out, the mortise-tenon joints occur extrusion deformation and the fiber of wood is cocked, while the column and beam are almost intact. The shape of hysteretic loops of all joints is Z-shaped and the gathering effect gets more obvious with the increase of loose degree. The rotation capacity, stiffness and energy dissipation capacity of the loose joints are significantly below the intact one and reduce gradually as the loose degree increases, while the joints have good deformation capacity under different loose degrees.By analyzing the test results, three kind of damage assessment methods including destruction-resistance-potential-based, double parameters of loose degree and destruction-resistance-potential-based and strength reservation-based were put forward and compared. The results indicate that the single influence factor is considered in destruction-resistance-potential-based and strength reservation-based damage assessment method respectively to evaluate the damage of the joints. The result is largely discrete, the method is not comprehensive, and the damage coefficient of strength reservation-based is small. While both loose degree and destruction-resistance-potential can be considered in loose degree and destruction-resistance-potential-based double parameters damage assessment method to evaluate the damage of the joints, and the damage assessment are comprehensive and reasonable.Based on the experimental research, finite element analysis software ABAQUS was used to simulate the properties of joints, the calculation results agreed with the results of test very well. Parametric analysis of joint was carried out based on the theoretical analysis. The friction coefficient, material property, loose degree, axial loading and size of joint were all considered as analysis parameters. The results show that: with the increase of the friction coefficient, parallel-to-grain elastic modulus, horizontal-to-grain elastic modulus and height of tenon, the moment and rotational stiffness of joints are improved, while the mechanical properties of joints was slighty affected by the parallel-to-grain compressive strength, axial loading and diameter of column. The degradation rate of moment and rotational stiffness of joints gets faster as the increase of loose degrees.