Study On Behavior Of Vibration Reduction For The Ladder Track In Urban Rail Transit

At present,urban rail transit has been developing rapidly as a most effective way to solve urban traffic problem in China. At the same time, with the vibration emission problems on the surrounding environment which cannot be neglected. The ladder track as an effective reduction vibration track structure grows up rapidly. However, the application of the ladder track in China actually is a patented technology from abroad. It is needed to explore whether the vibration behavior would coordinate with the interaction between the China rolling stock and the ladder track structure, and whether the damping effect of ladder track can be further enhanced.so it is necessary to study the behavior of vibration reduction for the ladder track, analyze its impact parameters, in order to give full play to the ladder rail damping performance for vibration, reduce the environmental impact of the subway, increase economic efficiency, which has a great significance.In this paper, rolling stock system dynamics model and rail-sleeper-tunnel model have been established respectively with the America fifth grade of track irregularity as an impulse excitation.The wheel-rail force which was solved from the rolling stock model by using time-varying mobile loading method were imported to the track model. So, the dynamic response of track structure subjected to moving rolling stock load in tunnel was simulated. Spectrum curve and one-third octave spectrogram vibration acceleration level were obtained by post-process of the dynamic response results.From the point of vibration reduction, the dynamic behaviour of the ladder track was studied and the correctness of the simulation model were proved by the comparing with the measured data of Beijing subway Daxing Line and Line 4. It could be used to analyze the parameters of rail structure and the simulation results showed that:(1) The impact of track irregularity became smaller with the speed droping. As a result, the wheel-rail force weakened and the maximum displacement of rail decreased. The acceleration of rail, track bed and side walls decreased and the amplitude of vibration were decaying from the rail to the track bed and the wall.(2) With the speed increasing, the vibration acceleration level of the beds and side walls of the DTⅥ2 fastener track and ladder track were increasing and the insertion loss of track bed and side wall were magnifying accordingly, and the damping effect of the ladder track was better. At the speed of 40~80km/h, the maximum insertion loss of one-third octave spectrogram vibration acceleration level of the track bed was about 20dB. In the frequency of 1 ~ 200Hz, the damping effect of the ladder track was 10 ~ 14dB.The sensitivity analysis of the ladder track structure parameters were done in order to explore and optimize its vibration damping behavior. The results showed that:(1) The stiffness and damping of the vibration damping pad, the fastener stiffness, the space of vibration damping pad and the length and mass of sleepers all had an influence on the damping effect of the ladder track. However, there was not an obvious improvement in the damping effect within the adjustable range of these parameters.(2) As a damping effective track structure, it is necessary to study the behavior of riding stability and durability for further application.