Study On Train Safety Control Of High-Speed Railway Bridge Under The Action Of Near-Fault Earthquake

Near-fault earthquake usually refers to the earthquake within 20 km from the fault.Due to its complex characteristics,its focal mechanism is completely different from that of far-field earthquake,so the structure will cause serious damage under its action.In this paper,the bottom wave is selected from PEER(Pacific Seismological Research Center of the United States),the artificial simulation pulse type near-fault earthquake is used by MATLAB software,and use Midas civil 2015 to build a 10-span 32 m double-track prestressed high-speed railway simple-supported girder bridge model,the train-rail-bridge coupling vibration analysis is realized by TTBSAS program,the correlation between pulse-type of near-fault vibration parameters and the response of the train-rail-bridge coupling system is explored,and get the most adverse impact condition.Finally,the traffic safety of simply supported beam bridge under near and far field earthquake is studied,and the specific safe speed threshold is given.The specific content and conclusions are as follows:(1)Artificial synthesis and verification of near-field earthquake.The characteristics of near-fault earthquake are described,and the process of pulse-type seismic simulation by MATLAB software is introduced in detail,the main steps are the determination of the equivalent pulse waveform,the selection of the equivalent velocity pulse,the determination of the position of the equivalent velocity pulse overlay and the simulation process of near-fault pulse-type seismic movement.Then the degree of conformity between synthetic seismic wave and actual near-fault pulse type ground motion is verified,including the coincidence degree of time history and the coincidence degree of frequency spectrum.It has been verified that the near-field seismic simulated by the simulation method and the program written in this article conforms to the characteristics of the actual recorded wave and is reliable.(2)Study on the correlation between seismic parameters and train-rail-bridge coupling system response.Firstly,the train-rail-bridge coupled vibration model under the action of earthquake is briefly introduced,and the finite element model was established with Midas Civil 2015 and imported into the TTBSAS calculation program developed by the research group,to analyze the response of pulsed ground motion parameters to the train-rail-bridge coupled system,including the influence of velocity pulse waveform,period of velocity pulse and peak value of velocity pulse.Finally,there are the comparison of bridge dynamic response,the comparison of orbital dynamic response and the comparison of vehicle dynamic response.The results show that the influence of pulse-type near-field seismic movement on train-rail-bridge coupled system response is significantly increased compared with that of non-pulse seismic motion,the pulsed type mainly affects the displacement and acceleration of the bridge,and the maximum increase is 110.86% and 40.08% respectively;The pulse period mainly affects the bridge and the rail subsystem,in which the mid-span displacement and acceleration of the bridge increase by 127.31% and 92.31%,respectively,and the mid-span displacement of the rail increases by 92.09%;When the pulse peak changes,the mid-span displacement and acceleration of the bridge increase by 202.58% and 67.51%,respectively,and the mid-span of rail displacement increases by 73.02%.(3)The effect of near-field seismic vertical effect on the seismic response of train-rail-bridge coupling system is discussed.Different vertical and horizontal acceleration peak ratios are set to explore the influence of vertical effect of near-field earthquake on the dynamic response of train-rail-bridge coupling system,including bridge mid-span displacement and acceleration,track mid-span displacement,body mass center acceleration,derailment coefficient,wheel load reduction rate and wheel lateral force.The results show that with the increase of the peak acceleration ratio,the lateral displacement of the bridge,the lateral acceleration,the track subsystem,the lateral acceleration of the car body,the derailment coefficient,the wheel load reduction rate and the lateral force of the wheel pair are basically unchanged,the derailment coefficient,the wheel load reduction rate and the lateral force of the wheel pair increase by 0.92%,1.60% and 0.49% respectively compared with the standard value of 0.65.Therefore,the influence of the vertical effect of the near-field earthquake on the dynamic response of the train-rail-bridge coupling system can be ignored in the calculation.(4)Study on traffic safety control of simply supported beam bridge under near-field seismic.It mainly discusses the variation of the new derailment evaluation index with the seismic intensity,and studies the safety speed threshold of high-speed trains passing through bridges under near and far field seismic.Finally,the specific safety speed threshold is given.According to the calculation results,under the excitation of ground motion intensity of 0.05g～0.15 g,the safety speed threshold of pulsed near-field motion is smaller than that of far-field motion,and the maximum difference is 100 km/h.When the near and far field seismic intensity is 0.20g～0.30 g,the corresponding safety threshold is200km/h.Therefore,the safety speed threshold of pulsed near-seismic is smaller than that of far-seismic,which has a greater threat to the safety of the train on the bridge,and it’s influence should be considered in the seismic design.The results show that the safety speed threshold of pulse-type near-field seismic movement is smaller than that of far-field vibration,when the ground motion intensity is0.15 g,the difference is the largest,which is 100 km/h.Therefore,near-field earthquakes pose a greater threat to the safety of trains on the bridge,and its influence should be considered in seismic design.