Research On Mechanical Characteristics Of Ballasted Track On Bridge Based On Coupling Of Discrete Element And Multi-body Finite Element Method

The high-speed railway foundation bridges in China account for a relatively high proportion.As the bridges have a large rigidity as the foundation of the discrete track bed,which leads to insufficient elasticity of the track structure,the ballast on the bridge is seriously powdered,and the maintenance and repair costs have increased dramatically.As China's high-speed railway operation speed and people's experience of riding comfort are further improved,this puts forward higher requirements for the service performance of the ballast bed on the bridge,so it is necessary to carry out more in-depth dynamic characteristics research on the ballast track on the bridge under high-speed conditions.In this paper,based on the coupling method of discrete element and multi-body finite element,a bridge-ballast track dynamic coupling model is established.Based on the coupling model,the variation of the mechanical properties of the ballast on the bridge along the longitudinal and transverse directions of the bridge was analyzed.The unfavorable area of the track bed on the bridge is determined.At the same time,the impact of different driving conditions on the mechanical characteristics of the track bed on the bridge was analyzed,and the vibration damping effect under the conditions of single vibration damping measures and combined vibration damping measures was studied.The main research contents and results of this article are summarized as follows:(1)Based on the coupling method of discrete element and multi-body finite element method,a bridge-ballast track dynamic coupling model under high-speed conditions is established,and the model verification is completed by comparing with the actual measurement and literature data.This paper is the first to propose a method based on the coupling of discrete elements and multi-body finite element method to study the mechanical characteristics of ballast tracks on bridges under high-speed traffic conditions,and solve the problem that the discrete ballast bed composed of ballast particles cannot interact with the upper and lower structures;The ballast track coupling dynamics model established on the high-speed railway bridge based on this method can not only consider the granular characteristics of the mesoscale ballast and the mutual occlusion and stacking relationship between the particles,but also reflect the interaction between themacroscopic overall track bed and the upper and lower structures.(2)Based on the coupling model,the mechanical characteristics of the ballast track bed in different areas on the bridge are analyzed,and the unfavorable area of the ballast track bed on the bridge is obtained.Based on the verified bridge-ballast track dynamics coupling model,the longitudinal and lateral changes of the track bed mechanical properties were studied.The research shows that the vibration acceleration of ballast bed and the contact force of ballast particles along the longitudinal direction of the bridge decrease first and then increase,with the maximum at the end of the bridge and the smallest mid-span area of the bridge;The change law of the cumulative settlement of the track bed is the opposite,the area near the middle of the bridge is larger and the beam end is the smallest;The dynamic response of the track bed in the lateral direction satisfies the largest area directly under the sleeper,followed by the area under the side of the sleeper,and the smallest area outside the sleeper.(3)Based on the coupling model,the influence analysis of the high-speed railway's different operating conditions on the mechanical characteristics of the ballast on the bridge was carried out.Based on the established bridge-ballast track coupling model,the effects of different driving speeds,different train axle weights and different bridge spans on the mechanical characteristics of the ballast track bed on the bridge were studied.The results show that as the train speed continues to increase and the axle load increases,the dynamic response of the track bed continues to increase,and the increase in the bridge span will reduce the contact force and ballast acceleration of the ballast particles in the mid-span area,but will increase the settlement of ballast bed;because the dynamic response of the track bed is greater when the driving speed is higher,certain damping measures need to be taken when the vehicle speed is higher.(4)Establish the coupling model of bridge-ballasted track under different vibration-damping measures.The effects of different vibration-damping measures on the mechanical characteristics of the track bed were studied.After analysis,suggestions for improving the vibration-damping measures of the ballast track bed mechanical characteristics on the bridge were given.Based on the coupling model,the effects of different stiffness cushions and different ballast cushions on the mechanical properties of the ballast bed on the bridge were studied.The effects of different stiffness under-pillow pads and different ballastunderlays on the mechanical characteristics of the track bed were studied;the results show that the application of different vibration-damping measures can improve the dynamic response of the track bed,but it will increase the structural deformation;The stiffness of the cushion is recommended to be in the range of 60?100k N/mm.Asphalt concrete cushion is recommended among the three ballast cushions.After combining the under-pillow cushion and the ballast cushion,the under-pillow cushion will exert the best vibration-absorbing performance The stiffness value has been changed compared to when it was used alone.In the combined vibration reduction measures,the recommended rigidity range of the under pillow pillow is 100?180k N/mm,and the asphalt ballast is recommended to use bituminous concrete cushion.As a result,it is found that the combined vibration reduction measures have not significantly improved the improvement of the mechanical properties of the track bed compared with the single vibration reduction measures,and will significantly increase the cost.Therefore,it is not recommended;As a result,the under-pillow rubber pads and asphalt concrete cushions have their own advantages and disadvantages in terms of the influence of different track bed mechanical properties,and should be selected reasonably according to the specific conditions on site.