Frequency-Dependent Dynamic Properties Of Rubber Pads In Rubber Floating Slab Track For Subway And Its Influence On Enviromental Vibration

As an efficient and convenient way to travel,subway not only promotes the rapid development of the city,but also attracts a lot of scholars’ attention to the environmental vibration caused by its operation.Therefore,it is urgent to set reasonable measures for vibration reduction and isolation.There are many types of vibration damping measures in subway.Rubber floating slab track is widely used for its good vibration damping performance and high cost performance.However,there are many factors affecting the prediction accuracy of environmental vibration of subway.Besides the dynamic parameters of soil in the model,train load and the parameters of track structure are also included.The dynamic behavior of polymer materials such as rubber is significantly related to the excitation frequency.However,most of the previous studies on environmental vibration regard elastic rubber pad as a constant spring-damping system.In order to accurately and scientifically predict the ambient vibration level along the subway line,it is necessary to systematically study and analyze the frequency-varying dynamic characteristics of the rubber pad in the rubber floating slab track.In this paper,the commonly used rubber floating slab damping track in subway is taken as the research object.Firstly,the viscoelastic dynamic characteristics of the elastic pad under the fastener and the floating slab with frequency nonlinearity are tested and characterized.Secondly,a dynamic frequency domain model of vertical coupling between metro vehicle and floating slab track is established,to analyze the influence of rubber pad frequency-varying characteristics on the natural vibration characteristics and transmission attenuation of track structure.On this basis,the influence on the vibration response of the wheel-rail system is further studied.Finally,a frequency domain prediction model of subway tunnel-soil layer is established based on the finite element method.The effect of frequency varying characteristics of rubber pad on ambient vibration is analyzed.The main contents are as follows:(1)By using the universal mechanical testing machine equipped with a temperature box,combining the principle of temperature frequency equivalence with WLF equation of the fractional Zener model and the fractional KV model,the broadband dynamic mechanical properties of the elastic pad under the fastener and the floating slab were tested and theoretically characterized respectively.The results show that: The storage stiffness and loss factor of the rubber damping pad increase with the increase of frequency in the predicted range of the given condition.In addition,the storage stiffness and frequency have a linear relationship in the double logarithmic coordinate system,while the loss factor and frequency have a linear relationship in the single logarithmic coordinate system.The fractional KV model can well characterize the frequency varying mechanical properties of the rubber damping pad.(2)The vertical vibration characteristics and transmission attenuation law of the rubber floating slab track system are obtained by harmonic response analysis on the basis of fully considering the frequency-varying characteristics of the two elastic rubber pads.Results show: The vibration of rail is greatly affected by the frequency varying properties of the rubber pad of the fastener,while the vibration of floating slab is greatly affected by the frequency varying properties of the rubber pad under the slab.Considering the frequency varying properties of the rubber pad under the slab,the transfer rate of the track structure force is reduced,and the attenuation rate of the rail and floating slab is reduced in the whole frequency band.(3)A frequency domain model of vertical coupling dynamics between metro vehicle and floating slab track is established.The effect of frequency varying dynamic performance of rubber pad on dynamic mechanical response of wheel and rail system in frequency domain is analyzed.The results show that the vibration level of the vehicle track system in the middle and high frequency band is generally amplified by the frequency-varying characteristics of the fastener rubber pad.The frequency variation of the damping pad of floating slab track has no effect on the rail vibration,but the vibration of the track slab is amplified to some extent in the full frequency domain.(4)The frequency domain prediction model of subway tunnel-soil layer is established based on the finite element method.The underside reaction force of the vehicle-rubber floating slab track coupling model is applied to the base ground of the tunnel,and the steady state dynamics analysis is carried out to obtain the attenuation law when the vibration is transferred to the ground.Results show: Considering the frequency varying properties of the floating pad,the vertical vibration of the ground will increase in the middle and low frequency range.Moreover,at different distances from the center of the line,the vibration level of the weighted acceleration on the ground increased significantly,with an increment of 5.5-7.9dB.In other words,the vertical vibration level of the ground will be underestimated to some extent without considering the frequency varying properties of the rubber pad of floating slab track.