Study On The Vertical Dynamic Behavior Of Recycled Plastic Composite Crosstie Ballast Structure

Recycled plastic composite crosstie is a new type of crosstie,which is made of recycled plastic,tires,paint and other hard degradable polymer materials with glass fiber as reinforcement and other chemical additives.it mainly applies to revenue line and urban transit line abroad.There is no precedent application in china passenger train line.one of the goals to apply plastic composite crosstie in Chenglan railway is to mitigate vibration of the track.This thesis's subject is to evaluate the effect on vibration mitigation and the effect on dynamic response of track structures.Most of the contents and conclusions are as below:Collect information of recycled plastic composite crosstie and survey its properties sufficiently.The recycled plastic composite crosstie is initially developed to substitute the wood tie.The time of application is short and the composites are complex,so the properties are not so clear.In general the composite crossties are light,high elastic and large damping coefficient.The plane dynamic mechanical models of composite crosstie and reinforced crosstie III are established.Another model is solid model of composite crosstie.The comparing results show that composite crosstie can reduce the rail acceleration which is advantageous to track vibration mitigation.It can reduce the ballast acceleration which is good for retarding pulverization of ballasts.The forces above crosstie and track bed are also reduced which is good for the crosstie and permanent displacement of track bed.However,the vertical displacements of rail,crosstie and track bed are increasing which is disadvantageous to track stability.As the composite crosstie's acceleration is large which is disadvantageous to top ballasts and the fasteners.The composite crosstie is made up with high polymer materials,large acceleration may lead to heat energy accumulation.The composite crosstie is still elastic,though the displacement is large.In order to optimize the composite crosstie ballast structure,the thickness of the ballast,the stiffness of the fasteners and the crosstie spacing are analyzed to offer reasonable values.(1)The stiffness between each track layer is stepped down and the converted vibration mass of track bed is increasing as increase of track bed thickness.The results show that the displacements of rail,crosstie,track bed as well as the rail acceleration are increasing.However,the acceleration of track bed,the pressure between crosstie and track bed are decreasing.All the rates of change are slowing down,and the amplitudes are not significant.Considering all above,the advised thickness of track bed is 0.4m.(2)The rail displacement and acceleration decrease with the fastener's stiffness,which is helpful to reduce rail stress.However,the displacements and accelerations of other components are increasing but not significant.Therefore increase the stiffness of the fasteners can mitigate the rail vibration and displacement.Take all above balance into account,the advised fastener stiffness can be 80MN/m to 90MN/m.(3)Decreasing the crosstie spacing is advantageous to reduce the displacements of rail,crosstie and track bed as well as the force between crosstie and track bed.When the crosstie spacing is 0.58m,there are inflection points in the displacements of rail,crosstie and track bed curves.When the crosstie spacing is 0.54m,there is another inflection point in track bed displacement curve.Therefore the advised crosstie spacing is 0.54m.