Research On Seismic Fragility Of Continuous Welded Track On Bridge Based On IDA

Our country is located between the Pacific Ocean earthquake belt and the Eurasian earthquake belt,is the most earthquake-disaster country in the world.As the life channel to the disaster area after the earthquake,the state of railway under the earthquake directly affects its life channel function.Based on this,this thesis took the seamless line of ballasted track on the(40+64+40)m continuous girder bridge as the research object,combined the finite element theory,earthquake engineering and the beam-rail interaction principle,and used numerical simulation method to analyze the dynamic response of the seamless line with ballast track on the bridge under the action of earthquake,determined the damage index of the seamless line of ballast track on the bridge,and based on Incremental Dynamic Analysis(IDA),has analyzed the seismic fragility of the bridge,in order to provide theoretical support for the seismic design,post-earthquake state evaluation and maintenance and repair of the seamless line on the bridge.The main research contents and conclusions are as follows:(1)Based on the finite element theory,the refined spatial coupling model of the seamless line of ballast track on the bridge under earthquake action is established,and the natural frequency and vibration mode shape of the first ten orders of the structure were determined,which laid a data foundation for the selection of seismic wave and structural damping parameters.(2)Taking the representative Northwest Calif-02 wave as an example,the peak ground acceleration(PGA)was used as the index of ground motion intensity based on the dynamic time history analysis method.The influence law of rail temperature variation range,longitudinal and transverse resistance of the track bed and other parameters on the seismic response index of the seamless rail on the bridge(the peak of the relative displacement of the beam and rail,the peak of the longitudinal force of the rail,etc.)was determined.Among them,the lateral relative displacement of the beam and rail was most affected by ground motion,that is,the seamless line of ballast track on the bridge was the first to undergo lateral damage under the action of earthquake;The peak of the lateral relative displacement of the beam and rail was most significantly affected by the amplitude of the rail temperature change and the lateral resistance of the track bed,and was basically not affected by the longitudinal resistance of the ballast bed.(3)Based on the determination principle of structural damage index,the response characteristics of seamless lines on bridge under earthquake action and the physical significance of specific parameters,the lateral relative displacement of the beam rail was used as the judgment index of the damage state of the seamless line on the bridge under the action of earthquake,and the damage state was divided into five states of no damage,minor damage,moderate damage,severe damage and complete failure according to the different values of the lateral relative displacement of the bridge and rail.(4)Based on the dynamic characteristics of the seamless line of ballast track on the bridge,15 seismic waves were selected and amplitude adjusted in increments of0.025 g from 0.025 g ～ 0.5 g according to PGA;The probabilistic demand model of the corresponding relative displacement index of beam and rail of the seamless line with ballast track on the bridge was obtained by IDA analysis method,and then the probability seismic fragility curve of the seamless line with ballast track on the bridge was determined according to the vulnerability function and damage index value of the probatic demand and the damage index value,and the influence of the change amplitude of track temperature and the lateral resistance of the ballast bed on the change law of the vulnerability curve was analyzed.When the PGA was 0.25 g,the overtake probability of serious damage reached 0.5,and the orbital temperature variation amplitude was approximately exponentially related to the overtake probability of serious damage(0.79 when the orbit temperature changed at 60 °C),and the lateral resistance of the ballast bed was negatively and linearly correlated with the overtake probability of severe damage(0.91 when the lateral resistance of the ballast bed was 50%).Therefore,in earthquake prone areas,it is necessary to optimize the design of seamless tracks as much as possible,increase the locked rail temperature,reduce the amplitude of rail temperature changes,and enhance the ability of seamless tracks on bridges to resist earthquakes;At the same time,in strict accordance with the requirements of seamless track maintenance rules,it is prohibited to carry out track bed maintenance operations in summer.