Study On The Vehicle-track Interaction During Earthquakes And The Early Warning Threshold Of High Speed Railway

China's high-speed railway has developed rapidly and its running mileage is constantly increasing.It currently exceeds 20,000 kilometers.By 2025,the mileage of high-speed railway will reach 38,000 kilometers,which can cover most large cities.The issue of earthquake prevention and mitigation of high-speed railways has been paid much attention to,which mainly involving two levels of issues: first,to ensure that the infrastructure meets the needs of seismic fortification,there are already relatively mature design standards.The second problem is the safety of vehicle operations during earthquakes in terms of infrastructure safety.This problem has not yet got an effective and reliable solution.In order to deal with the threat to the operational safety of highspeed railways by earthquakes,in addition to the anti-seismic design of high-speed railway structures,Japan and other countries have adopted earthquake early warning methods.When the predicted ground motion reaches a certain threshold,vehicles will be decelerated or stopped to reduce damages.During the construction process of some highspeed railways in China,earthquake monitoring models have been prepared in advance for use in earthquake early warning.However,China's research on earthquake early warning has just started,and less experience can be referred to.Related parameters such as the reasonableness of an earthquake early warning threshold still need further research and verification.The high-speed railway earthquake early warning system mainly aims at three sorts of problems: the first is to predict the intensity of the ground motion of destination,which mainly involves the use of the smaller first-arrived ground motion detected early to predict the size of the subsequent destructive ground motion of the destination;The second is to determine the threshold of the ground motion for early warning of earthquake,which is closely related to the operational safety of the vehicles under the earthquake;the third is the transmission,release and control methods of the early warning information,which mainly includes the technical methods of transmission and release,control strategies and methods.This article mainly studies the issues related to high-speed railway wheel-rail dynamic response analysis and the determination of high-speed railway earthquake early warning threshold under earthquake.The main work and related conclusions are as follows:(1)The vehicle-track model shaking table test was used to validate the dynamic response of the vehicle-track model and its derailment mechanism under earthquakes.Experimental research shows that the current standards and specifications on the limit values of the wheel load reduction rate and derailment coefficient of the vehicle may be too conservative.The reason for the derailment of the vehicle is the large horizontal vibration of the track structure due to the earthquake,which causes the wheels to shake horizontally,prompting the left and right wheels and the rails to alternately separate,causing the vehicle to roll sideways and eventually cause the derailment.Based on the above derailment reasons,it is shown that in addition to derailment evaluation criteria such as derailment coefficients and wheel load reduction rates under earthquakes,the amount of wheel lift and relative displacement of the wheel/track should be utilized as derailment evaluation criteria.When the recorded seismic wave is applied to the vehicletrack model,the peak value of each wheel-rail dynamic response indices under different working conditions is extracted and analyzed.It is important to note that the wheel-rail dynamic response value of the vehicle-track model under the action of artificial waves is the most significant.The preliminary inference is that,because the natural frequency of the vehicle-track model in the horizontal direction is the closest to the superior frequency of the artificial wave,the dynamic response indices of each wheel/track under the action of the artificial seismic wave is the largest.Test results of applying horizontal and vertical seismic waves to the vehicle body are basically the same as those of applying horizontal seismic waves alone.This shows that during the earthquake,the horizontal seismic waves have a greater impact on the dynamic response of the vehicle-track system.Vertical seismic waves have less influence on it.(2)A two-dimensional vehicle-track dynamics numerical model is put in place in this paper.The analysis and calculation results of the two-dimensional vehicle-track numerical model are compared with the vehicle-track model shake table test results,which show the calculated results are basically consistent with the test results.This indicates that the numerical calculation results are reliable.This article also studies the impact of the frequency of seismic waves on the normal driving of the vehicle.It is found that when the excellent frequency of the seismic wave is close to the horizontal natural frequency of the car body,resonance is easy to occur,and it is harmful.Therefore,when designing the track of the vehicle,try to keep the rolling natural frequency of the vehicle body away from the low-frequency region.When the height of the subgrade changes within a specified range,the seismic wave has little effect on the wheel lift off the vehicle,horizontal contact force of the wheel-rail and fluctuation of the vertical-contact force response of the wheel-rail.(3)Based on the principle of vehicle-track dynamics,a three-dimensional finite element calculation model of a multi-rigid vehicle-track is established in this paper,this paper also separately studies "the effect of vehicle speed on the dynamic response of vehicle wheels and rails when the track irregularity is not considered" and "the effect of vehicle speed on the wheel and rail dynamic response of earthquakes when the track irregularity is considered".The study of track irregularity mainly refers to the American track irregularity spectrum,and the inverse Fourier transform method is utilized to numerically simulate the power spectrum function.The code in MATLAB is used to draw the U.S.six-level track line spectrum.Finally,by using ABAQUS subroutine,a track irregularity spectrum is applied to a track in a three-dimensional model of vehicle-track dynamics.When the track irregularity is not considered,the calculation results show that the change of vehicle speed under the earthquake condition has a small effect on the dynamic wheel/track response of the vehicle.The curves are compared with the static vehicle-track model shake table test,and it is thought to be basically in agreement with the test results.This shows that the wheel-rail dynamic response of the vehicles at rest in the earthquake is close to the wheel-rail dynamic response when the vehicle is operating at a uniform speed on smooth tracks.Therefore,the stationary state of the vehicles under earthquake action can be approximated as a state where the vehicle runs on a smooth track at a uniform speed.When the track irregularity is considered,the peak acceleration of the seismic wave is 0.3g,the wavelength range of the track irregularity is(0.5m ? 80m),and the speed range of the vehicle is within 100km/h to 300km/h.The impact of the track dynamic response peak shows a clear linear growth trend,but not by much;When the track irregularity is considered,the train speed is 300km/h and the peak acceleration of El-Centro seismic wave is 0.04 g,the wheel load reduction rate of the vehicle-track system is 0.6567,which have exceeded the safety limit of wheel load reduction rate stipulated in the specification.Therefore,0.04 g can be considered as the earthquake warning threshold of high-speed railway.However,it is far from enough to study the dynamic response of vehicle wheel and track under the action of a single seismic wave.By utilizing the twodimensional vehicle-track numerical calculation model,this paper analyzes the dynamic response calculation of the vehicle-track numerical model in the case of earthquakes.The operation state of the vehicles under the earthquake is considered as the superposition of the two states of "the vehicle is running on the uneven track" and "the vehicle is running on the straight track under the earthquake".(4)This paper proposes a new idea for determining the threshold for earthquake early warning.The derailment index such as the derailment coefficient and the wheel load reduction rate is calculated by the following static methods under the earthquake,and the safety redundancy of the two derailment indicators is used as the derailment coefficient limit of the stationary state of the vehicle and the wheel load reduction rate limit.Consequently,the high-speed railway earthquake warning threshold could be determined,by using the derailment coefficient limit and the wheel load reduction rate limit,and the different derailment coefficient limits and different wheel load reductions assess for the stationary vehicles are given.The warning threshold system is built according to the rate limit;Finally,by imputing 80 typical horizontal seismic waves for calculation,the relationships between the "wheel lift","horizontal displacement of wheel-rail contact point","vehicle overturning angle" and the "peak ground acceleration" in the calculation results are statistically analyzed.Based on the concept of random vibration,an earthquake early warning threshold evaluation table for the vehicles under earthquake action is given.