Seismic Response Analysis Of High Piers Of Railway Bridges

The western region of China has high mountains and deep valleys,and the railway high pier simply supported beam bridge is a widely used bridge type.Unlike medium and low piers,high piers exhibit significant higher-order vibration mode effects in seismic response.Due to the large cross-section and significant self weight of railway bridge piers,the influence of higher-order vibration mode effects is also amplified,which can have adverse effects on bridge safety;High pier bridges usually have reinforced steel bars placed at the bottom of the piers.However,due to the complexity of the seismic response of high pier structures,improper placement of reinforced steel bars may lead to the formation of new seismic weak areas on the piers,posing serious safety hazards.Therefore,a reasonable arrangement method is very important.The current seismic specifications for highway and railway bridges in China do not have clear regulations for bridges with pier heights exceeding 40 m.With the popularization of railway high pier bridge construction,in order to ensure the safety and smoothness of high pier bridges under earthquake action,it is necessary to systematically and comprehensively study the response distribution characteristics of railway high piers under earthquake action.In response to the above issues,this article takes a simple supported beam bridge of a passenger and freight railway as the research background,selects four different heights of bridge piers as the research object,establishes an elastic model and a fiber model of the bridge piers,and conducts dynamic characteristics analysis,response spectrum analysis,and incremental dynamic analysis successively.Based on the seismic response results of the bridge piers,the study is conducted.The main content includes the following aspects:(1)Establish a Midas/Civil finite element model,first conduct modal analysis to analyze the dynamic characteristics of different pier heights,and then conduct response spectrum analysis to separate the maximum displacement,bending moment,and shear force distribution of the pier body under a single mode of vibration.Study the contribution of the first three modes of vibration to seismic response under three factors: different pier heights,site conditions,and pier beam mass ratio,Summarize the influence of higher-order vibration modes on high piers of railway bridges under elastic conditions.(2)Establish an Open SEES fiber model to analyze the bending moment and curvature of each section of the bridge pier,collect and organize the yield moment,yield curvature,ultimate bending moment,and ultimate curvature of the section,and draw the envelope curve of the pier body for the axial compression ratio and elastic stiffness of the section,analyzing the performance level of sections at different heights of the pier;Conduct dynamic characteristic analysis and elastic seismic response analysis on the Midas model and Open SEES model,and compare the analysis results to ensure the consistency of the parameters of the two models.(3)Three Seismic wave suitable for the bridge site are selected for incremental dynamic analysis of four piers,and the research is carried out according to the seismic response results,including the bending moment curvature curve of the pier bottom section,the time history of pier top displacement and pier bottom curvature,and the characteristics of seismic response distribution along the pier shaft.The seismic response results of piers of different heights are compared and the influence of high-order vibration mode effect is analyzed.(4)The 67 m and 82.5m piers are equipped with reinforced steel bars in the lower part,which has a good protective effect on the bottom section of the pier.However,under certain seismic conditions,there may be a sudden increase in curvature at the cut-off point of the reinforced steel bars,which is not conducive to the safety of the structure.In addition,high piers may experience damage in the middle of the pier before the bottom of the pier under strong earthquakes,and appropriate reinforcement bars need to be arranged in the middle of the pier.Therefore,This article discusses the reasonable cut-off position and quantity of reinforced steel bars for the arrangement of high piers.