Comparative Study On The Dynamic Response Feature Of Long-span Rigid Railway Bridge Excited By Near-fault And Far-field Earthquake Ground Motions

With the continuous development and improvement of railway network,the high-pier and large-span continuous rigid railway bridges have been increasingly emerging.If the bridge is close to active fault,its seismic risk will be greatly increase.While there is still less research on the high-pier and large-span continuous rigid railway bridges under near-fault earthquake.Therefore,it necessary to study the response characteristic of these bridges under near-fault earthquake and to provide reference for the seismic design of such bridges and related norm.In this paper,taking a high-pier and large-span continuous rigid railway bridge as the main object,two full-bridge finite element models with vehicular-load(VL-model)and without vehicular-load(NVL-model)are built.The natural vibration characteristics of the two types of bridges models are compared,and are analyzed with response spectrum method and elastic-plastic dynamic and time-historical analysis.Then taking the full-bridge considering the upper live loads as the study objective,the seismic response characteristic of the high-pier and large-spancontinuous rigid railway bridge excited by near-fault and far-fault ground motions arestudied,and the responses of bridge with different pulse parameters are contrastively analyzed.The main research work in this paper are as follow:(1)Taking a high-pier and large-span continuous rigid railway bridge as the mainobject,two full-bridge finite element models with vehicular-load(VL-model)and without-load(NVL-model)are built.The natural vibration characteristics of the two types of bridges models are compared.The results show,the participating coefficient of first mode mass is significantly declining compared with that of regular medium and small bridges,and high vibration mode and pier mass contributes greatly to the structure’s seismic responses.(2)Based on code for seismic design of railway engineering,the response spectrum method analysis of the two types of bridges under frequently occurred earthquake and design earthquake are studied.The results show that,section internal force responses of main pier increase considering the live vehicle loads,the demand growth amplification of internal fore of the high pier bottom is greater than that of low pier.Therefore,in the seismic design of high-pier and large-span continuous rigid railway bridge,the vehicular live load of bridge superstructure should be considered.(3)Taking artificial seismic wave as the loads,the dynamic and time-history analysis of two full-bridge finite element models with vehicular-load(VL-model)and without-load(NVL-model)are studied.The results show,the plastic yielding all occurs on the pier top of main pier of the two types of full-bridge.Considering the,the displacement ductility capacity of main pier decreases significantly,the pier top plastic rotation increases remarkably,and the displacement of pier top also increases.(4)Based on the mixture simulation method for artificial near-fault ground motion,are generated.Then taking the full-bridge considering the upper vehicularlive loads as the study objective,the response characteristic of high-pier and large-span continuous rigid railway bridge under far-field earthquake and thenear-fault ground motions considering directivity effect and fliting-step effect areanalyzed contrastively.The results show that,the response of bridge under thenear-fault earthquakes with pulse are greater than under far-field earthquake.Excited by near-fault earthquake,the directivity effect has greater influence for the responseof bridge than fliting-step effect.