Study On The Seismic Performance And Seismic Mechanism Of Traditional Timber Structure In Song Dynasty

Existing ancient Chinese architecture,particularly timber building,is the carrier of historical memory,cultural development,and civilization progress.Thanks to its excellent structural performance,the traditional timber building can even stand for thousands of years,providing important materials for the study of Chinese traditional culture and ancient architectural techniques.However,due to environmental erosion,the effect of sustained load,and occasional disasters,the bearing capacity and deformability of these existing timber buildings have been largely reduced.The repair and reinforcement of these buildings is the main way to prolong their life,and improving or restoring their seismic performance is an important part of the repair and reinforcement work.Scientific research on the seismic performance of the traditional timber structure and rationally revealing their seismic mechanism are the important prerequisite for seismic strengthening of the existing timber structures,and the important reference for the repair work.Based on the requirements of seismic strengthening work of ancient timber building and with the support of National Natural Science Foundation of China(Grants No.51338001 and 51278324),this paper takes the traditional timber structure of Chinese Song dynasty as the research object,and a half-scale whole timber structure model involving a column frame layer and Dou-Gong layer was designed and made according to Yingzaofashi.Six quasi-static tests were carried out on the model.The hysteretic behavior of the overall timber structure,the column frame layer and the Dou-Gong layer was studied.The effects of vertical load and loading courses on the seismic performance of the timber structure were analyzed.The seismic mechanism of such timber structure was revealed from an energy perspective.The main research results are as follows:(1)Through the two-stage tests of initial loading and repeated loading,the hysteretic behavior,deformation and bearing capacity,stiffness variation characteristics and energy dissipation features of the overall timber structure under different vertical loads were studied.The changes in bearing capacity,stiffness and energy dissipation of the timber structure due to repeated loading was quantitatively analyzed.The reaserch results showed that,under different lateral displacement amplitude and varying loading courses,the decline of the bearing capacity,the stiffness and the energy dissipation of the timber structure due to repeated loading were 5%-24%,1%-36% and 4%-26%,respectively.However,the deformation and energy dissipation capacity of the timber structure were hardly affected by the loading courses,and the structure behaved a good ability to withstand multiple lateral loads.(2)The hysteretic behavior of the column frame layer and the Dou-Gong layer were analyzed based on the quasi-static tests conducted on the whole timber structure.The results showed that the bearing capacity and stiffness of the column frame layer were much lower than that of the Dou-Gong layer.The Dou-Gong layer remained in an elastic state when the column frame layer has yielded or even nearly turned over.The column frame layer played a decisive role in the structural energy dissipation,and more than 80% of the energy dissipation of the timber structure come from the column frame layer in the six tests.The hysteretic characteristics of such timber structure were completely reflected by that of the column frame layer.(3)The restoring force features of such timber structure could be characterized by a bilinear reinforced elasto-plastic model.The effects of vertical loads and loading courses could be reflected in the differences in the stiffness of each characteristic segment of the model.The theoretical analysis of the restoring force of the timber structure showed that,the restoring force of such timber structure were mainly come from the rocking of column and the bending moment of mortise-tenon joints.(4)The seismic mechanism analysis based on energy conversion showed that,the energy input to the timber structure was mainly converted into hysteretic energy and elastic strain energy when the displacement amplitude of the timber structure was small.With increasing displacement amplitude,the influence of the storage of gravitational potential energy on the seismic resistance of the structure become more and more significant.Under large deformation,about 60% of the input energy could be converted into the gravitational potential energy and stored in the timber structure,which greatly reduced the damage of the wood components.This energy conversion mechanism is the main way for such timber structure to resist repeated earthquakes,especially large earthquakes,and an important reason for the weak energy dissipation and good seismic performance of such timber structure.Moreover,the simulation analysis results of the seismic mechanism of the timber structure using Abaqus finite element software are in good agreement with the experimental results.