Study On The Probabilistic Seismic Damage Character Of Simply Supported Girder Bridge Under Fault-crossing Earthquakes

Due to the restriction of geographic and geomorphic conditions,the route selection designs and construction cost,it is inevitable to utilize bridge to cross active faults.However,in several major earthquakes in recent years,a number of bridges crossing the fault were damaged or collapsed severely.At present,the domestic and foreign researches for seismic design of bridge are still in the initial stage.Especially,the study on vulnerability of fault-crossing bridges is still blank.In this paper,taking a simply supported girder bridge crossing fault as the research object and the artificial fault-crossing ground motions with slip effect as the excitation,considering the influence of uncertainty of ground motions and structural parameters,the seismic probability damage characteristics of typical simply supported girder bridges under fault-crossing earthquakes were analyzed based on the IDA analysis method.The main research contents in this paper are illustrated as follow:(1)The domestic and overseas research status of the seismic analysis of fault-crossing structures were combed.According to the seismogenic characteristics of strike-slip fault,the fault-crossing ground motions with slip effect were generated by the combination of low frequency artificial pulse and high frequency earthquake records,and the characteristics of the ground motions with the slip effect are analyzed.(2)The OpenSEES finite element software was used to establish the finite element model(mean model)of the full bridge,and the rationality of the model was verified with the SAP2000 finite element software.At the same time,the uncertainty of the structure level,the material level and the boundary conditions(all known as the structural parameter uncertainty)were considered based on the Latin Hypercube Sampling(LHS)method,thus 20 full bridge finite element numerical models(stochastic models)were established.(3)Using the nonlinear IDA analysis method,the mean models and the random models were analyzed.The IDA curves of the pier bottom curvature were drawn and the distribution characteristics of these IDA curves under different ground motions were summarized.The corresponding the probability distribution curves were obtained by the statistical analysis of two types of model calculation results.According to the damage grades of the pier,the damage state of structures under different ground motion intensities were evaluated.The comparative analysis of the probability distribution curves utilizing the two kind of model shows that the uncertainty of the structural parameters will increase the discreteness of structural responses.(4)Through the statistical analysis of above IDA results,the vulnerability curves of the mean model and random model at each damage level were obtained,therefore the seismic performance of the bridge can be evaluated.Different effects of the uncertainty of the ground motions and the structural parameters on the structural response were quantitatively analyzed.The results shows that,the influence of the ground motions uncertainty is larger and the influence of structural parameter uncertainty is relatively smaller.The seismic risk assessment of a case bridge was carried out based on the IDA analysis results.The evaluation results from multiple views show that all kinds of evaluation curves based on IDA can well reflect the seismic performance of structures.