Study On The Mechanical Performance Of Traditional Residential Wooden Structures

Fire,rainstorm,earthquake as well as some secondary disasters(such as mountain rock slide,debris flow,etc.)caused by rainstorm and earthquake inevitably cause damage to traditional residential wooden structures.Hence,repair and protection are required for traditional residential wooden structures containing the excellent Chinese culture,and the systematic and in-depth study of mechanical performance of traditional residential wooden structures is the premise of protection and repair.Mortise and tenon joints(MTJs)in wooden structure buildings are the key parts of the structure,which have a great impact on the mechanical performance of the whole structure under earthquake.Meanwhile,a large number of earthquake damage investigation data show that the floating column foot joints of wooden residential buildings are prone to have excessive displacement under earthquake,which will cause the wooden frame to tilt and even the structure to collapse.In addition,traditional wooden dwellings in mountainous areas are vulnerable to impact loading such as rock slide and debris flow.Although the probability of impact loading is much lower than that of quasistatic load,it often leads to disastrous consequences due to its short duration and high peak value.Therefore,to analyze mechanical properties of the mortise and tenon joints of the traditional wooden dwellings,to carry out the relevant research on the limiting-displacement reinforcement of the floating column foot joints,and to explore the impact resistance of traditional wooden dwellings,have a distinct engineering application background and great significance of cultural value protection.In view of the above background,this paper mainly carried out the following work:(1)The low-cycle repeated loading test was carried out on the side joint specimens of traditional wooden dwellings in Guizhou.This paper analyzed the influence of beam height,beam width and joint form on the seismic performance of the joint,gave the suggestion that straight penetrated mortise-and-tenon joint with wooden peg(SPMTJ/WP)should be preferred in the traditional dwelling construction from the perspective of performance.On this basis,the mechanical mechanism of SPMTJ/WP was analyzed,the working states of the joints were divided,the judgment condition of each working state was given,and the moment-rotation mechanical model of SPMTJ/WP considering the influence of looseness between mortise and tenon was established.After the accuracy of the mechanical model was verified by the experiment,the factors such as the joint size and the degree of looseness that affect bending performance of the joint were analyzed parametrically.(2)The low-cycle repeated load tests were carried out on five wooden frame specimens with different column foot joint,and the effects of different column foot joint forms on the seismic performance of the wooden frame were compared.From the performance point of view,it was proposed that column foot joint strengthened by circular sleeve should be used for the limiting-displacement reinforcement of the floating column foot joint.In order to obtain the optimal engineering design parameters of the circular sleeve used for reinforcement,the FEA was carried out on the wooden frame specimen with the column foot joints strengthened by the circular sleeve.After the model was verified via the experimental,the factors such as height and diameter of the circular sleeve were analyzed parametrically,the key and non-key factors affecting the lateral performance of the wooden frame were obtained,and their reasonable value range were determined.In addition,based on the semi-rigid assumption of the joint,the bending characteristics of the MTJ and the bending characteristics of the column foot joint were respectively obtained through the moment-rotation mechanical model of the MTJ and the FEA data of the wooden frame,and then the load-displacement curve of the wooden frame was derived by using the structural analysis method,so as to provide a reference for the lateral performance design of the traditional residential wooden structure.(3)Under five different air pressures,the split Hopkinson compression bar tests were carried out on three grain directions(longitudinal direction,radial direction and tangential direction)of Chinese fir(Cunninghamia lanceolata).The dynamic mechanical properties of Chinese fir in different grain directions were analyzed and studied,and the dynamic amplification coefficient function curves of compressive strength of Chinese fir in three grain directions were fitted according to the scatter diagram of experimental data.Through the drop hammer impact test,the failure mode and dynamic response of wooden beam under different placement directions were analyzed and studied.The experimental results showed that the wooden beam specimens cracked or broke during the impact process;The peak impact force of the wooden beam specimen increases with the increase of impact height;The shape of the impact time history curve includes two types.The type Ⅰ include pulse segment and peak segment,while the type Ⅱ include pulse segment,peak segment and sub-pulse segment.(4)Based on the results of the research on the dynamic mechanical properties of Chinese fir,the monotonic static load test of wooden beams and the drop weight impact test,combined with the research results of many scholars on the strain rate effect and the relevant code for the calculation of the bending capacity of wooden beams,the ultimate bearing capacity of wooden beams under impact was estimated.The method of estimating the peak impact force under impact load was verified via the experimental data and proved to be reasonable.