Study On Mechanical Properties Of Typical Mortise-Tenon Joints Of Traditional Timber Buildings In Jiangsu And Zhejiang Province

There are many traditional timber buildings built during the period of Ming and Qing Dynasties in Jiangsu Province and Zhejiang Province, their structural types are mainly post-and-lintel construction and column-and-tie construction. Due to the long-term erosion of wind and rain, war damage, earthquake damage, etc, there are a lot of damages in different degrees for these ancient timber buildings, scientific conservation of these timber buildings have been very urgent. The assessment of structural safety is the base of the scientific conservation, and the mechanical properties of mortise-tenon joints are the key problems of the structural safety assessment. In this paper, first, the typical mortise-tenon joints in Jiangsu and Zhejiang province were surveyed and analyzed, then, the four types of typical mortise-tenon joints which are Tou mortise-tenon, Ban mortise-tenon, Mantou mortise-tenon, Zhi mortise-tenon at the foot of short column were chosen and the relevant experimental models were designed. Finally, with the methods of experimental research and finite element simulation, the mechanical properties of these four types of typical mortise-tenon joints were analyzed in detail. The main conclusions of this study are summarized as follows:According the relevant standards, the compressive strength parallel to grain, the tensile strength parallel to grain, the shear strength parallel to grain, the bending strength, the modulus of elasticity and the moisture content of the timber are tested. Based on the principle of orthogonal symmetric, the stress-strain relationship is deduced by elasticity theory. The elastoplastic parameters of the timber are calculated by using the empirical formula and generalized hill yield criterion, the elastic-plastic constitutive model of the timber is presented.These four types of mortise-tenon joint specimens are tested under reversed cyclic vertical loading in this paper. The final failure mode of Tou mortise-tenon joint is the fracture of tenon. The final failure mode of Ban mortise-tenon joint is the pulling out of tenon. The final failure mode of Mantou mortise-tenon is the fracture of mortise. The final failure mode of Zhi mortise-tenon is the pulling out of tenon. The skeleton curves of these mortise-tenon joints can be simplified as trilinear model with elastic stage, yield stage and failure stage. The regularity of rigidity degeneration of these mortise-tenon joints is summarized, the coefficient of displacement ductility and the capability of energy dissipation are compared among these four types of mortise-tenon joints. The results show that in terms of displacement ductility, the type of Zhi mortise-tenon joint is the best, the type of Mantou mortise-tenon joint is the second, the types of Ban mortise-tenon joint and Tou mortise-tenon joint are the last. In terms of energy dissipation capacity, the type of Ban mortise-tenon joint is the best, the types of Tou mortise-tenon joint and Mantou mortise-tenon joint are the second, the type of Zhi mortise-tenon joint is the last.In this paper, considering the material non-linearity and the contact non-linearity, the finite element models of these four types of mortise-tenon joints are established to study their mechanical properties under in-plane loading by ANSYS software. The results of numerical analysis well coincide with those of the experimental results, which verifies the feasibility of nonlinear numerical simulation. Then, the mechanical properties of these four types of mortise-tenon joints under the out-plane loading and the torsion loading are studied and analyzed. The final failure modes, the relationship of bending moment and rotation angle, the regularity of rigidity degeneration of these mortise-tenon joints are analyzed. Finally, the rigidity ratios of these four types of mortise-tenon joints under in-plane loading, out-plane loading,and tortion loading are presented.