Study On The Mechanical Mechanism Of Straight Mortise-tenon Of Traditional Wooden Structure

According to the different structure system,the traditional wooden structure is mainly divided into two forms,Post and Lintel Construction and Column and Tie Construction.Post and Lintel Construction is mainly distributed in the north of China,while Column and Tie Construction is mostly built in south.Because of the traditional wooden buildings has been damaging by wind and rain,the war and earthquake,the buildings that was remained has some damages,such as the looseness of mortise-tenon joint and tenon was pulled out.The incline of Dougong,and some structural remembers appeared decay,worm-eaten,crack,aging,bend and so on.Which directly affects the safety and longevity of buildings.Straight mortise-tenon joint is a critical joint in traditional wooden structure,there is a gap in it,due to the drying shrinkage of the wood,and cause it to become loose,and then affect the seismic performance of the wooden structure.Therefore,the mechanical mechanism of through-tenon joint and continuous-tenon joint in traditional wooden buildings was intensively studied in this paper,by experimental research and theoretical analysis.Three specimens with different height were made to study the seismic performance of the continuous-tenon joint.The moment-rotation hysteretic loops and skeleton curves of the continuous-tenon joint was obtained by low-cycle reversed loading experiment,and degradation of stiffness,energy dissipation and deformation capacity were studied.In addition,the embedment model of through-tenon joint and continuous-tenon joint was constructed by analyzing the mechanical mechanism of joints,the moment-rotation calculation formula of them was deduced by establishing the relationships of forces,materials and geometries.Finally,The experiment of theloosen through-tenon joint and continuous-tenon joint of the research group were used to verify the correction of the theoretical analysis,good agreement was found between theoretical and experimental data.And the influence parameter that the moment-rotation relationship of two kinds of joints were analyzed,the conclusion is as follows:(1)The experiment of continuous-tenon joint shows that the joint not damaged when it had a big rotation angle,the beam slipped and appeared large plastic deformation because of pressure comes from mortise,and the wood fiber is cocked.The gathering effect of hysteretic loops of joint gets more obvious with the increase of height of the beam.It indicated that the beam slipped along with its stiffness increases.In the elastic stage,the initial rotational stiffness of the joint increases slowly with the increase of height of the beam due to slipping.The joint has a good ductility and a large bearing capacity,which still not destroyed when the rotation angle exceeds 0.2rad.The energy dissipation capacity of the joint decreases with the increase of the height of the beam.(2)Looseness is a main influence factor to the relationship of moment-rotation of through-tenon joint.The positive and negative bending moment,initial rotational stiffness of the through-tenon joint decreased with the increasing of the looseness,but the amplitude of bending-moment decrease before the joint yields is greater.And there is a linear change between looseness and rotational stiffness of the joint;the bending moment and rotational stiffness of the joint increased as the friction coefficient increased under the positive and negative loading,and the positive is bigger than the negative,but the amplitude of increment is small.The positive and negative initial rotational stiffness,bending moment of the through-tenon joint increased,with the increase of the small tenon length and the compressive elastic modulus of the perpendicular grain of the wood,and the increment is larger.(3)the initial rotational stiffness and bending moment of continuous-tenon joint decreased with increasing of looseness,but the amplitude of bending-moment decrease before the joint yields is greater,and the yield point become hysteresis;As the friction coefficient increases,the rotational stiffness of the joint increases,but the increment is small.The flexural capacity of the joint also increased,but the amplitude of the increment is bigger after the joint yield.(4)With increasing of the height of the beam and the compressive elastic modulus of the perpendicular grain of the wood,the stiffness and flexural bearing capacity of continuous-tenon joint increased.But the influence of the elastic modulus is more obvious,which made the yield point forward,however,the increase of the height of the beam is conversely.