Mechanical Behavior Analysis Of Ancient Building Sixth-class Timber Structure Under Deteriorated Column Base

Chinese timber structures with a resplendent history of thousands of years are the crystallization of the wisdom of ancient Chinese architectural craftsmen and are a dazzling pearl in China’s historical and cultural heritage.Many existing timber structures can still stand upright after many earthquakes,which is enough to show the excellent seismic performance of Chinese timber structures.However,with the increase of time and the influence of environment and other factors,ancient building wooden structure column foot will appear decay,material deterioration and other damages,which will have a great impact on the load-bearing performance and seismic performance of timber structures.Therefore,studying the impact of the material degradation of the column footings on the load-bearing performance and shock-resistant performance of the wooden structure of timber structures can better protect the timber structures.In this paper,according to the relevant regulations on the size of each component of ancient buildings in the "Ying Zao Fa Shi",the finite element software ABAQUS is used to establish a six-level intact wooden frame model and a degraded wooden frame model of column footings,and perform quasi-static analysis on the models respectively.Loading test and dynamic loading test.The research content mainly includes the following three aspects:（1）Low-cycle reciprocating loading experiments were performed on the intact wooden frame under different vertical loads,and the deformation characteristics,hysteresis characteristics,stiffness curve and energy conversion relationship of the wooden frame were obtained during the loading and unloading process.The consequences indicated that the column foot of the wooden frame during the loading process It will rise and fall repeatedly but there is almost no slipping phenomenon,and the joints of the tenon-and-mortise joints will be drawn and squeezed out.As the vertical load increases,the bearing capacity and lateral stiffness of the timber frame are increasing.During the loading process,the energy input into the wooden frame is mainly converted into hysteretic energy consumption,gravitational potential energy and elastic strain energy.At the beginning of loading,there is only elastic deformation between the various components,and at this time,the elastic strain energy accounts for a relatively large amount;as the loading continues,the proportion of gravitational potential energy and hysteretic energy consumption gradually increase,which is the main conversion method in the later stage of loading.（2）Low-cycle reciprocating loading experiments were proceed on wooden frames with different degrees of degradation of the column footings,and compared with the hysteretic characteristics and stiffness of the intact wooden frame model.The results show that the more serious the deterioration of the material properties of the column foot,the smaller the restoring capacity,bearing capacity and rigidity of the wooden frame model.From the energy point of view,the material degradation of the column footing will reduce the total energy input into the wooden frame.During the energy conversion process,the gravitational potential energy will decrease and the elastic strain energy will increase.The hysteretic energy consumption mainly comes from the tenon and tenon joints,so the material degradation of the column foot has little effect on the hysteretic energy consumption.Whether it is an intact or a wooden frame with degraded column footings,the increase in vertical load will improve the load-bearing performance and rigidity of the wooden frame.（3）Perform dynamic loading simulation experiments on the intact timber frame and the timber frame with degraded column footings.First determine the natural vibration period of each wooden frame model.Secondly,simple harmonics with invariable frequency,different amplitude,invariable amplitude and different frequency are applied to the wooden frame model to obtain the dynamic response of the model such as acceleration and displacement.Finally,the influence of the material degradation of the column footing on the dynamic response of the timber frame natural vibration period,the acceleration and the relative displacement is studied and analyzed.The results indicate that the deterioration of the material properties of the column feet will increase the natural vibration period of the wooden frame.Whether it is to change the amplitude or frequency of the harmonics,the more serious the deterioration of the material properties of the column foot,the larger the relative displacement,and the smaller the acceleration response.And the greater the harmonic amplitude and the smaller the frequency,the greater the impact of the material degradation of the column foot on the response of the wooden frame acceleration and displacement.Similar to the pseudo-static force,the sliding of the timber frame column foot during the dynamic loading process is very small and can be ignored.