Research On Seismic Behavior Of Straight Tenon Timber Frame With Joint Damage

The ancient building wood structure is a precious resource left by the ancient ancestors to the later generations with rich cultural characteristics of the times,and has a very high social and historical value.The wood structure of ancient buildings has experienced vicissitudes of life,witnessing the changes of the times,it is difficult to avoid material aging and structural decay,cumulative damage and deformation,and this situation will gradually deteriorate with the continuation of time,so the study of ancient architecture wood structure and protection is of great significance.The timber frame composed of two columns and one loquat is an important force-bearing structure in ancient timber structure.The roof and paving load are supported on the top of the structure,and the bottom of the structure is connected with the foundation,the mortise joints dissipate energy and reduce vibration,and the column foot joints slide and isolate vibration.The damage of mortise joints and column foot joints will lead to the decline of the seismic performance of the structure,and the structure will incline or even collapse.Therefore,it is of great significance to study the changes of seismic performance of timber frame under different damage of mortise and tenon joints and column foot joints for the appraisal,evaluation and maintenance and reinforcement of existing ancient timber structures.In this paper,the unidirectional straight tenon-timber frame is taken as the research object.Through model test and numerical simulation,the force transfer mechanism and seismic performance of the frame are studied,and the changes of seismic performance of the timber frame under different damage of tenon and column foot are analyzed.The main contents are as follows:(1)This paper expounds the physical and mechanical characteristics of timber and related testing methods,summarizes the common tenon-mortise connection types of ancient timber structures,analyses the mechanical mechanism of tenon-mortise joints and column-foot joints of unidirectional tenon-timber frames,and the theoretical analysis of the skeleton curve of unidirectional tenon-timber frames in the forward loading stage is analyzed.(2)In order to study the effect of the decay damage of tenon-mortise joints and column-foot joints on the seismic performance of unidirectional straight tenon timber frame,considering the different degree of tenon damage and surface damage,three kinds of decay damage tenons were made by different artificial damage simulation methods.One kind of decay damage of column-foot consisted of four damaged timber frames.In addition,a non-destructive timber frame model and column foot damage reinforcement timber frame were made.The horizontal low-cycle repeated loading tests were carried out on the six models the scale of 1:3.52,which were made according to the Song Dynasty Construction Formula.The strain variation characteristics of tenon-mortise joints and column-foot joints,hysteretic characteristics,stiffness degradation and energy dissipation capacity of the timber frame,as well as the variation rules of the seismic performance of the timber frame during horizontal repeated loading were compared and analyzed.(3)Using ABAQUS,a large-scale general finite element analysis software,the above six different types of unidirectional tenon timber frames are simulated and analyzed by finite element method.The actual artificial damage is simulated by dividing the tenons into different areas and reducing the wood properties in the damaged area.The stress mechanism and possible failure modes of unidirectional tenon-mortise joints and column-foot joints are verified from three aspects:the deformation of tenon-mortise joints and column-foot joints under low cyclic repeated loading,the distribution of Mises stress and equivalent plastic strain PEEQ,and hysteretic curves and the comparison of test and simulation skeleton curves.The results show that the finite element model established in ABAQUS is in good agreement with the model test by loading simulation analysis,which proves the rationality of finite element simulation.