Study On The Degradation Law Of Seismic Performance Of Ancient Wooden Structures Considering Joints Damage

As a main connection method of wooden structure joints,mortise-tenon connection has excellent bending resistance and deformation resistance.At the same time,it can dissipate seismic energy through friction and has good seismic performance.However,due to the erosion of the natural environment for a long time and the impact of natural disasters such as earthquakes,the joints of ancient wood structures will inevitably produce different degrees of damage,reducing the bearing capacity of ancient wood structure,to a certain extent,shorten its service life.Therefore,it is of great significance to study the seismic performance of the damaged mortise and tenon joints and the seismic performance of the overall structure of the wooden structure considering the damage of the joints,which is of great significance to the protection of the ancient wooden structure,and can also provide a theoretical basis for the future research of the wooden structure.In this paper,the parametric analysis of mortise-tenon joints considering damage was carried out,and the bending moment-rotation curve of the damaged state was obtained.Based on the theater of Huaijun Office in Baoding,the finite element model was established,and compared with the shaking table test results to verify the rationality of the finite element model.The seismic vulnerability analysis of the theater model under three working conditions of intact,damaged,damaged and time-varying nodes was carried out,and the failure probability of the theater structure under three working conditions was obtained.The specific research contents of this paper are as follows:(1)The finite element software ABAQUS was used to establish the tenon-mortise joint model,and the correctness of the finite element model was verified by referring to relevant literature and combining with the tests.The main types of joints damage and the degree of damage were investigated and analyzed,and the parametric analysis of crack shape,worm damage,tenon height and width was carried out to study its influence on the seismic performance of mortise and tenon joints.The worm-eaten joints have a significant impact on the bearing capacity,and the bearing capacity of joints with insect-eaten damage rate of6.9% and 12.5% decreased by 24.5% and 46.7% respectively compared with intact joints.The bending moment-rotation curve of the joint considering the coexistence of multiple damages was obtained by coupling multiple damages(insect damage,tenon height loss).(2)Based on the theater of Huaijun Office in Baoding,the intact theater model and the joint damaged theater model were established.,and two types of theater structural models were compared and analyzed from three aspects: acceleration,base shear force and story displacement.The results show that the displacement of the top of the first floor column of the theater model considering the joint damage is about 2.1 times that of the first floor column of the intact theater model under the action of the rare earthquake of eight degrees.The acceleration is about 3.0 times.With the increase of earthquake action,the difference between the two is more significant.(3)Twelve seismic waves were selected,the seismic vulnerability analysis of the theater model under three working conditions under the dual influence of intact,damaged,damaged and time-varying nodes was carried out,and the exceeding probability of the structure under different damage states was studied.The results show that the failure probability of the theater structure increases with the increase of ground motion intensity under three working conditions,and the slope of the corresponding seismic vulnerability curve increases first and then decreases.After the PGA reaches 0.60 g,the probability of the theater structure collapsing under three working conditions is 2.05%,7.52% and 24.73%respectively.