Frequency Domain Response Of High-speed Railway Under Failure Of Under Rail Support

In the transportation network of our country,high-speed railway plays an increasingly important role with its convenient,stable and efficient transportation efficiency^[1].The earliest high-speed railway has been in service for more than ten years in China.With the increase of the number of train operation,the service state of ballastless track is gradually declining,among which the fastener is loose and invalid,the track plate is hollowed out,the subgrade settlement and other diseases are increasingly serious,and even pose a threat to the safety of high-speed train operation^[2].However,these diseases occurred in the support under the track need to be properly reflected in the response characteristics of vehicles,tracks,bridges and subgrade structures under different diseases.The corresponding model cannot be too simple to cause that the main aspects and influencing factors of the dynamic response of the system cannot be reflected or too complex,which makes the analysis of the dynamic response process very complicated.Based on this,this paper will establish an analysis model which can reliably evaluate the impact on the operation of high-speed railway for three diseases:fastener failure,track slab void and subgrade settlement.The relevant research results will provide relevant data reference for the relevant departments of railway system in daily management and maintenance.In order to characterize the influence degree of different diseases on track structure and train in detail,the vertical coupling model of high-speed vehicle track bridge and the finite element model of crts-i slab track are established in this paper by using the idea of dynamic flexibility and the finite element theory.Combining the power flow theory with the characteristics of frequency domain analysis,the vibration energy evaluation method of track structure is used to study the influence of three kinds of support failure on track structure.The main conclusions are as follows:（1）Taking crts-ii slab ballastless track as the analysis object,the failure of single fastener and the failure of three consecutive fasteners are compared with the normal conditions.With the increase of the number of fastener failures,the dynamic flexibility amplitude of rail,track plate and base plate increases significantly,and the peak value in the frequency range moves to the lower frequency segment.The change at the bridge is relatively small Small.The failure of fastener will cause the attenuation rate of each layer of track structure to increase in the lower frequency range.The overall trend of the vertical force amplitude of wheel rail in different fastener failures is similar,but with the increase of the number of fastener failures,the frequency corresponding to the peak value becomes smaller,and the value of the peak value is relatively lower.In the higher frequency band within the study frequency range,the vertical force of wheel rail in fastener failure increases,and the impact rises due to the increase of the number,which has a hidden danger to the driving safety.In terms of the distribution of vibration energy,the peak value of vibration energy of each layer of the track will move to the low frequency direction due to fastener failure,and there is obvious jump phenomenon in the frequency range of 110-200hz.Under normal working conditions,the vibration energy transfer rate between rail and track plate is relatively large,and the transfer rate between other layers does not change much.（2）Taking crts-i slab ballastless track as the research object,two common types of slab end void and slab in void are selected,and the void length is set as 0.31m,0.94M,1.56m,2.19M and 2.81M respectively,which is compared with the normal working condition.The dynamic flexibility of rail,track slab and bridge will be affected when the length of track slab void increases,and the change range is low at 0.31m and 0.94M.Compared with the rail and bridge,the vibration energy of the track plate increases with the increase of the void length,and the transfer rate between the rail and the track plate increases with the increase of the void length,while the transfer rate between the track plate and the bridge is the opposite.The vibration energy at the track plate is greatly affected by the void of the track plate,which will form energy concentration at the track plate.When the end of the slab is empty,when the length of the void reaches 1.56m,the peak value of each index of the dynamic flexibility of the track bridge structure increases significantly,the peak value of wheel rail interaction force decreases due to the weakening of the overall rigidity of the track,and the peak value of the vibration energy of the rail,track slab and bridge changes abruptly and migrates.When there is void in the track slab,the dynamic flexibility amplitude,phase angle and attenuation rate of the track bridge structure are less affected.Relatively speaking,the influence of slab end void on the track is significantly greater than that of slab end void.Under the influence of slab end void,the track will lose support laterally,which will lead to the weakening of track support force and the aggravation of track structure response,and then have a serious impact on the service life of the track.（3）According to the actual situation of high-speed railway subgrade in China,this paper analyzes the stress and deformation characteristics of crts-i slab track under the action of cosine differential settlement of subgrade section,as well as the influence law of track structure dynamic flexibility and vehicle acceleration under different settlement amplitude.With the uneven settlement of subgrade,the track structure will produce the following deformation due to the gravity effect,and the deformation presents the phenomenon of warping at both ends and similar to the settlement wave type in the middle.When the settlement amplitude is fixed,with the increase of the settlement wavelength,the void range between the track structure and the subgrade will increase,and then fit again.When the settlement amplitude is fixed,the deformation of each layer of the track structure is basically the same.When the wave length of uneven settlement of subgrade is consistent,the stress trend of track structure under the influence of different settlement amplitude is that the upper surface of each layer in the settlement center is the maximum value of compressive stress,while the two sides are the maximum value of tensile stress;when the settlement wavelength is fixed,with the increase of settlement amplitude,the peak value of tensile stress of track plate changes from less than compressive stress to greater than compressive stress,while the phenomenon of base plate Similar.With the increase of settlement amplitude,the rail dynamic flexibility amplitude and wheel rail interaction force increase rapidly.When the settlement wavelength is 15 m,and the settlement amplitude is 10 mm,the vertical acceleration of the bogie and wheel set of the vehicle is twice of that without settlement.More attention should be paid to the uneven settlement of the subgrade with the settlement wavelength of more than15 m.