Seismic Vulnerability Analysis Of Long-span Railway Cable-stayed Bridge System Based On OpenSees

With the development of high-speed railways in China,large-span railway bridges have been extensively constructed.However,earthquakes have occurred frequently in recent years,and as bridges play an important role in the transportation lines,any damage of bridges due to earthquake will not only directly affect transportation capacity,but also cause unpredictable economic losses.Therefore,it is very necessary to carry out seismic analysis of bridges,especially for the long-span ones.The frequent occurrence of earthquakes have also promoted the development of seismic theory.Performance-based seismic design is an advanced method with reasonable seismic performance targets and seismic measures,which has important guiding significance for bridge design.In this thesis,a lot of research was carried out on a long-span railway cable-stayed bridge.A nonlinear finite element model of the bridge was firstly established with the help of OpenSees for the nonlinear dynamic time-history analysis.Then the vulnerability of bridge components was studied with incremental time-history analysis method.Finally,based on the boundary estimation method of reliability theory,the fragility curves of the bridge system were obtained.The main contents of this thesis are as follows:1?The large-span cable-stayed bridges constructed in China in recent years were listed and the damage types of bridges under earthquake were summarized.Besides that,the development of the seismic design theory and both domestic and foreign research status of the seismic vulnerability of bridges were introduced.2?A three-dimensional finite element model of the cable-stayed bridge was built by OpenSees.And the bridge modeling process and the simulation of the main components are described in detail.Based on the model,the dynamic characteristics of the bridge were calculated.3?The process of incremental dynamic analysis for bridge seismic vulnerability was combed,and the damage criterion and damage index in this method were systematically summarized.The damage index of the bridge was determined by calculation,and finally the ground motion meeting the demand was artificially synthesized in accordance with the site type of the bridge.4?The seismic response of cable-stayed bridges is calculated by nonlinear dynamic timehistory analysis method,then on the basis of that,the vulnerability of bridge components was studied with the capacity-demand ratio model.Firstly,the vulnerability of bridge components was studied with one-dimensional ground motion input,and the vulnerability of longitudinal direction was compared with that of transverse direction.Secondly,results under the input of multi-dimensional ground motion wer studied and compared with the one-dimensional results.Finally,the effect of traveling wave effect on the vulnerability of bridges to earthquakes was considered.5?The series and parallel model were discussed.A system model of this cable-stayed bridge was established according to the structural characteristics.Based on the basic theory of system reliability,the first-order boundary estimation method and the second-order boundary estimation method were used to obtain the fragility curves of the cable-stayed bridge system,and a comparative analysis was carried out.