Study On Mechanical Properties Of Key Joints And Column Frame In Traditional Timber Structure

Traditional timber structure is an important carrier of traditional culture.Under long-term effects of environmental,extermal loads and human damages after hundreds of years,the damages of wood material,joints and components increases with the fatigue corrosion and material aging of wood.All these damages interact with each other,which can reduce the reliability and stability of the structures and even lead to the local failure or overall collapse of the structures seriously.In order to repair and protect the traditional timber structure with high cultural and historical values,it is necessary to carry out systematic and in-depth researches on its mechanical properties.Joints,as the weak part of the structure due to the weak cross-section,show important influences on the strength,stiffness and ductility of the whole structure.Therefore,the analysis of the mechanical performances of key joints and the simplified model of the joints are the prerequisites for accurate analysis of the overall mechanical performances and state assessment of the structures.In this paper,the researches on the mechanical performances of floating column foot joint and loose penetrated mortise-tenon joint are carried out.The working states and corresponding judging criteria for the floating column joint and the loose penetrated mortise-tenon joint are given.Theoretical models of residual moment,rotation moment for column foot joint,the load-carrying-capacity of column and the bending moment for loose penetrated mortise-tenon joint with considering the asymmetry and gap values are established for the whole working states,which includes the geometric,material and load parameters.Theoretical models are verified by full-scale tests and numerical simulations.Deformation characteristics and stress states of the column foot and the mortise-tenon joint under cyclic load are analyzed,and parametric analyses on the mechanical performances of joints are conducted.The calculation formula of impact factor for parameter is proposed.The sensitivity analysis of the parameters is carried out.The most sensitive parameters to affect the mechanical performances of column foot joint and penetrated mortise-tenon are vertical load and the tenon height respectively.Based on the theoretical model,numerical simulation and full-scale test,the equivalent finite element simplified models of the floating column foot joint and the loose penetrated mortise-tenon joint are proposed.This study provides a solid technical reserve for the establishment of the whole finite element model for the traditional timber structure.With the rotating spring units that can reflect the movement mechanism and mechanical performances of the joints and the pole unit representing the beam(fang)and column,the single timber frame is established to improve the calculation efficiency of the structures.The simplified single timber frame is verified by the solid finite element model.The lateral resistance and ultimate state of the frame are analyzed.The influences of the variable stiffness joint on the mechanical behaviors of the frame,and the contributions of the column foot and the mortise-tenon joint to the whole restoring moment of the frame are studied.Research results can provide a favorable calculation basis for the overall mechanical performances,state assessment,protection and repair of the traditional timber structure.Figures:126,tables:15,reference articles:119.