Research On Threshold Of Earthquake Early Warning For The Safe Running High-speed Trains On The Continuous Girder Bridge

In China,percentage of bridge total length is high in high-speed railway,which passes through multiple seismic belts.High speed and high-density continuous operations result in the train crossing the bridge more probability affected by earthquakes than the previous.At present,the earthquake early-warning system has been established for its high-speed railway in Japan,France and Taiwan,but the early warning system of China's high speed railway is still in the development stage.It is necessary to further analyze the actual situation of China's high speed railway to meet the requirements of the safety of high-speed railway running.The main contents of this paper are as follows:Based on rigid body dynamics and vibration mode superposition method,the model of four axle vehicle and bridge are established.It is assumed that the contact relation of wheel-rail is tightly in vertical and linear creep force in the horizontal.Taking track irregularity as the self excitation of the system,a unified dynamic equation of vehicle-bridge is set up.Newmark-beta method is used to solve the problem,which is programmed by the FORTRAN language.32m single span simply supported girder bridge is analyzed.The derailment coefficient,wheel load reduction rate,vertical and lateral train body acceleration,mid-span deflection and transverse amplitude of the bridge are calculated referring to the results of actual train-bridge vibration test from the relevant literature.The reliability of the program is verified.On the basis of vehicle bridge model,seismic load is taken as the external dynamic excitation input of the system.The dynamic model of train-bridge is established for the seismic analysis.Then the train-bridge response of a 60m+100m+60m three span continuous girder bridge for the seismic analysis is calculated.Five seismic waves are selected on the PEER website according to the site conditions.The calculation results show that:the response of train-bridge has different degrees of increase by the earthquake.There are differences in the existence of different seismic waves.With the increase of input seismic excitation,the derailment coefficient even exceeds the code limit,which is not safe for the train running.Taking the derailment coefficient less than 0.8 and the rate of wheel load reduction less than 0.6 as the control index,the threshold of earthquake early warning for the safe running high-speed trains is analyzed for the 60m+100m+60m three span continuous girder bridge.Different seismic waves corresponding to different threshold of peak value of horizontal acceleration.Due to overall considerations of running safety,thethreshold of peak value of horizontal acceleration for the 60m+100m+60m three span continuous girder bridge is recommended as 50Gal.Based on the M-R discriminant method,the range of the epicentral distance R in the warning area is obtained.