Optimization Design For The Structure Of Monobloc Sleeper Ballastless Track On Mixed Passenger And Freight Railway

Demand for rail freight in our country is increasing year by year,and the ballastless track on mixed passenger and freight lines can share some of the freight pressure while meeting passenger demand.In this dissertation,monobloc sleeper ballastless track is selected as the research object,whose bed slab thickness,rubber cushion stiffness and fastener stiffness are researched to conclude the effect on the track characteristics though quasi-static mechanical calculation,dynamics mechanical calculation and fatigue calculation.Some of the parameters of the monobloc sleeper ballastless track on mixed passenger and freight railway are recommended at the end.Through the quasi-static calculation of the track structure with different parameters,it is found that the geometric shape of the track would be conductively maintained and the stress on each structure of the track could be reduced as well under the train load with the thickness of the bed slab increasing.The internal warping stress of the bed slab peaks at a thickness of 350 mm under temperature gradient.The vertical displacements of the rail and the bed slab as well as the longitudinal tensile stress of the bed slab all decrease as the stiffness of the rubber cushion increases.Fastener stiffness change affects most on the rail,for the vertical displacement and dynamic bending stress decrease with the increase of fastener stiffness.When the rubber cushion stiffness is less than 100MPa/m or the fastener stiffness is below 40kN/mm,the vertical displacement of the rail exceeds the recommend limit.The calculation result of wheel-rail coupling dynamics shows that comparing the situation when passenger trains passing through to the situation of freight trains,the maximum vertical accelerations of the train and the track structure are larger while the maximum vertical displacements are smaller,and the response of the freight train to the stiffness change is greater than that of the passenger trains.The increase in the stiffness of the rubber cushion would significantly increase the vibration intensity under the action of freight trains,while the change under the action of passenger trains is relatively small.Meanwhile the deformation of the track structure would alleviate following the increasing stiffness of rubber cushion in both cases.The increase in fastener stiffness could relieve the stress and deformation of the rails,however the vertical acceleration of the rail itself would increase when the passenger trains passing through,and the vibration intensity of the bed slab together with the support layer would increases as well.With the same track structure under the action of train load,the number of freight train load cycles the bed slab could bear is nearly two orders of magnitude less than the number of passenger train load cycles.Under the combined effects of train load and temperature gradient,the temperature gradient affects more on the fatigue life of the bed slab,and the number of fatigue cycles can be tolerated by bed slab would go down to the minimum when the thickness is 350 mm.The increase of the stiffness of the rubber cushion could improve the fatigue property of the bed slab,while the rate of increase in the number of fatigue cycles becomes smaller when the stiffness reaches to 300 MPa/m.The increase in fastener stiffness would reduce the number of days under fatigue cycles the track bed slab can withstand in a small range.Based on the comprehensive calculation results,the recommended thickness of the bed slab is 450 mm,and the stiffness of the rubber cushion is 300 MPa/m,while the fastener stiffness is 50 kN/mm.