Research Of Dynamic Characteristic Of Ballast Track On Bridge Based On Nonlinear Properity Of Ballast Bed

Ballast track is one of the major forms of track structure in our country,with advantages of good elasticity,low cost,convenient maintenance as well as good noise absorptiption perfomance.As the railway constantly advances in the direction of higher speed,the vehicle vibration intensifies especially on the basis of bridge,but the passengers' demand for the comfort grows.It is important to study the dynamic characteristic of the ballast track on bridge.The simulation model for the ballast triaxial test is built based on the discrete element method which is used to analysis its deformation property.Then coupling model of vehicle-ballast track-bridge is built which contains nonlinear elastic ballast bed model.Based on the finite element model,the influence of the nonlinear elasticity of the ballast bed on its dynamic performance is analyzed.Also,the dynamic characteristic of the coupling system on the different line conditions is studied.At the same time,the influence of fastener stiffness as well as the stiffness and thickness of the elastic cushion on its dynamic characteristic is also analyzed in the paper.The major work and conclusion are as follows:(1)The static and dynamic triaxial test is done based on the DEM model.The paper studies the influence of confining pressure,gradation,load frequency and amplitude on the mechanical characteristics of ballast aggregate.Based on the nonlinear elastic model of ballast aggregate,fitting parameters are obtained.The influence of confining pressure and granular gradation on deviatoric stress-axial strain law is studied by static triaxial test.Then the influence of load frequency and amplitude on resilient property and plastic strain is studied by dynamic triaxial test.This paper summarizes the nonlinear elastic characteristics(E? = k1?k2=)of ballast aggregate and obtains its fitting parameters based on the results of the dynamic triaxial test simulation,where k1 =31.1 and k2 = 0.35.(2)Based on the nonlinear elastic characteristic of the ballast bed,the finite element model of vehicle-ballast track-bridge is built and verified.The influence of the nonlinear elasticity of the ballast bed on its dynamic performance is also analyzed.By using the ABAQUS user subroutine,nonlinear elastic ballast bed model is built.Then the coupling model of vehicle-ballast track-bridge is built and verified to analyse the influence of nonlinear elasticity of ballast bed on its dynamic performance from the safety index and the dynamic response index of track structure.By setting nonlinear elasticity which controls the stiffiness increase of ballaste bed with its stress incrase,we can obtain more accurate simulation results.(3)Based on the vehicle-ballast track-bridge model,its dynamic characteristic on the different line conditions is analyzed.Also,this paper studies the dynamic characteristic of the coupling system on the different fastener stiffness.Using the coupling model,its dynamic characteristic on the condition of different train speed and axle load is analyzed.It shows that dynamic response increases with the increase of the train speed and axle load.When necessary,damping measures should be taken to ensure safety and comfort of the train on bridge.At the same time,the coupling system dynamic response on the condition of different fastener stiffness is obtained,where the stiffness of the fastener on condition of bridge foundation is suggested to be 40?80kN/mm.(4)Dynamic model of vehicle-vibration damping track-bridge is built to analyze the influence of stiffness and thickness of sleeper pad and ballast mat on its dynamic performance.Based on the model of ballast track with elastic sleeper or ballast mat on bridge,the vibration damping perfoemation of two vibration damping track is obtained.The paper also studies the influence of stiffness and thickness of the sleeper pad and ballast mat on its dynamic performance,which shows that reasonable stiffness should give full play to the damping performance and ensure safety of the train.The stiffness of the sleeper pad is suggested to be 50MPa/m?100Pa/m and the thickness is suggested to be 30mm.The stiffness of the ballast mat is suggested to be 100MPa/m-200MPa/m and the thickness is also suggested to be 30mm.