Research On Hysteretic Model Of Key Components And Structural Seismic Analysis In Traditional Timber Structures

The traditional timber structure,which bears the long-standing culture of the whole Chinese nation,is an important historical heritage in China.Although most have survived the earthquakes,obvious damage also could be observed.In order to take more effective reinforcement and rehabilitation measures to ensure the safety of traditional timber structure,it is necessary to make a reasonable assessment of the structure safety under earthquake.Firstly,based on the stress mechanism and damage characteristics of the key components of traditional timber structure,simplified mechanical models were established,which can consider material properties,component size and other factors,as well as hysteretic models.Subsequently,shaking table tests were carried out on a scaled model taking the Xi’an Bell Tower as the prototype,and the influence of wood-infilled wall on the seismic performance of the structure were analyzed.On this foundation,combined with the hysteresis models of key components,a beam-spring finite element model(FEM)of traditional timber structure was established,and the rationality and effectiveness of the FEM was verified by shaking table tests.Finally,based on the structural damage index,the vulnerability assessment of traditional timber structure with two ground motion parameters was carried out.The main researches and conclusions in this paper are as follows:(1)Based on the extrusion deformation characteristics of timber,simplified mechanical model of common mortise-tenon joints,including the unidirectional straight tenon joint,semi-penetrated tenon joint,penetrated tenon joint,dovetail tenon joint and hoop head tenon joint,were established,which could take into account the wood properties,dimensions,friction,gaps and other parameters.An unified hysteretic model of mortise-tenon joints considering the shrinkage and slip characteristics was also established.The accuracy of simplified mechanical models and hysteretic model were verified by existing test data.(2)Based on the vertical deformation characteristics of Dou-Gong,the formulas for calculating the vertical stiffness of Dou-Gong under different loading stages were established.Based on embedding model of timber block and bending failure characteristics of beam,the simplified mechanical models of palace Dou-Gong and fork-column Dou-Gong under horizontal loading were established,respectively.Based on the characteristics of hysteretic curves of Dou-Gong,hysteretic models were established.The validity of simplified mechanical models and hysteretic models were verified by related tests data.(3)Based on the failure characteristics of masonry filled walls confined by timber frame,a simplified triple line mechanical model was established,which was characterized by yield point,peak point and ultimate point.Based on the extrusion deformation characteristics of timber,a simplified bilinear line mechanical model of wood filled walls confined by timber frame was established.Combined with the characteristics of hysteresis curve and based on the hysteretic model of mortise-tenon joint,the hysteresis model of wood-filled wall was also established.The models of infilled walls were validated by tests data.(4)A scaled model of Xi’an Bell Tower,considering the the influence of wood-infilled walls,at a 1:6 geometric scale was manufactured and shaking table tests were conducted.The failure modes,dynamic characteristics,dynamic responses,lateral stiffness and energy dissipation characteristics of the two structures under different earthquakes were compared and analyzed.The results show that the infilled timber walls significantly increases the natural frequency of the structure,as well as the lateral stiffness.The inter-story displacement and the proportion of plastic deformation energy dissipation were effectively reduced reslting in lower damage in the structure.Although the acceleration responses were obvious increased,the shock absorbing characteristics of traditional timber structure remained unchanged.(5)Based on restoring force characteristics of key components of traditional timber structure,a beam-spring FEM model was established.And based on energy dissipation principle,the damage assessment model of traditional timber structure was also proposed.Then the seismic fragility surface analysis on the traditional timber structure considering two ground motion characteristics(amplitude and frequency spectrum)were conducted.Comparative analysis was also conduct with the fragility curves only considering single ground motion parameter.The results show that the probability of traditional timber structure in damage state can be evaluated adequately by damage-based seismic fragility analysis with multi ground motion intensity parameters.