| In order to meet the demand of high speed railway for high speed and high comfort, high stability, comfort and reliability of train lines are needed. But because ballastless track is long-term exposed to complicated natural environment during operation and affected by train load and temperature, track structure system will appear all kinds of diseases and damage inevitably, such as track slab warping, CA mortar void, fastener stiffness change, etc. And furthermore, various forms of diseases may appear in combination, which will cause certain influence to the stability and safety of operation. Therefore researching the influence of various diseases and their combination on high-speed wheel-rail system dynamic performs and getting the allowable limit of typical disease is the key problem in ballastless track maintenance and repair.In this paper, according to field investigation of ballastless track damage in China, disease features of CRTS I prefabricated slab track are researched. Based on wheel-rail system dynamics theory, train-slab track coupling dynamic model and method for space is established, and the influence of void under the slab, fastener stiffness change, temperature gradient and multiple combined damage on wheel-rail system dynamic response is deeply and comprehensively analyzed, meanwhile the influence characteristics and allowable limit of typical diseases and damage is researched, hoping to provide certain guidance and reference for operation maintenance of high-speed ballastless track.(1) Train-track coupling dynamic model for spaceOn account of structural and technical characteristics of CRTS I prefabricated slab track, the train-track model is simplified accordingly. Based on wheel-rail coupling system dynamics, finite element method and ANSYS/LS-DYNA software, train-track coupling dynamic computing model for space with typical diseases is established, and the selection of main calculation parameters is researched. In virtue of existing research results and test data, the computing model is tested.(2) The influence of void below the slab on the dynamic characteristics of wheel-rail systemDynamic characteristics of wheel-rail system under different mortar void width, length and position and different running speed has been analyzed. The results show that, larger void below slab causes a significant increase in the rate of wheel load reduction, which could seriously affect operation safety. So the recommend value of void below the slab is limited to less than 1.Om.If the CA mortar void below the slab is not cut-through, the void has less effect on train dynamic response, but large effect on track dynamic response. If the the CA mortar void below the slab is cut-through, when the void length is less than 1.0m, the void has less effect on train and track response effect; when the void length is larger than 1.0m, the effect increases obviously; especially when the void length is 1.6m, the rate of wheel load reduction,0.82, exceeds the limit, and the rail vertical displacement,1.92mm, is close to the limit. With the train speed increases, the dynamic action of wheel-rail system increases significantly; when the void length is 1.4m and train speed is 350km/h, the rate of wheel load reduction reaches 1.0. The rate of wheel load reduction can be estimated through the displacement difference between adjacent rail protection; when the train speed is 300km/h and the displacement difference is 0.95mm, the rate exceeds 0.8, and when the train speed is 350km/h and the displacement difference is 0.5mm, the rate exceeds the limit.(3) The influence of fastener stiffness changes on the dynamic characteristics of wheel-rail systemThe dynamic response of wheel-rail system has been computed and analysed under the condition of overall change and mutation of fastener stiffness. The results show that the fastener stiffness change has little effect on train body vibration, namely the driving stability, but large effect on the rate of wheel load reduction, especially when the stiffness has a mutation, the rate increases notably, which could have greatly effect on safety of high-speed running. Therefore, the mutation of fastener stiffness should be strictly controlled, and the abnormal fastener of stiffness mutation must not appear at the region of running speed 350km/h.When the fastener stiffness increases from 20kN/mm to 120kN/mm overall,the load reduction rate increases from 0.34 to 0.6, indicating that the overall increase of fastener stiffness has adverse influence on operation safety. The most adverse distribution of 2 abnormal fasteners is both fasteners appear in the same slab cross section. The most adverse distribution of 3 abnormal fasteners is 2 abnormal fasteners appear under one rail with a distance of double fixed wheel base and 1 abnormal fastener appears under the middle of another rail. With the increase of driving speed, the rate of wheel load reduction increases obviously; when the driving speed reaches 300km/h,2 abnormal fasteners can make the rate reach 0.89,3 abnormal fasteners can make the rate reach 1.(4) The influence of combined action of void below the slab and fastener stiffness change on the dynamic characteristics of wheel-rail system.On account of combined action of void below the slab and fastener stiffness, dynamic response characteristics of wheel-rail system has been computed and analyzed. The results show that, when the fastener stiffness is 20kN/mm and the void length is 1.2m, the rail vertical displacement,2.14, has exceed the permitted limits, therefore, the fastener stiffness should not be less than 30kN/mm; when the fastener stiffness is larger than 80kN/mm, wheel-rail vertical force fluctuates significantly and the load reduction rate increases greatly, therefore, the replacement of rubber pad should be considered when fastener stiffness reaches 80kN/mm because of aging. When the void below the slab and abnormal fastener appear together, the rate of wheel load reduction increases significantly with the running speed increasing, and the rate reaches 1.0 with the running speed of 300 and 350km/h, therefore, the inspection should be strictly controlled to prevent the void region under the high-speed railway track slab appearing abnormal fasteners.(5) The influence of combined action of temperature gradient and void below the slab on the dynamic characteristics of wheel-rail system.Through applying bending to simulate temperature gradient, on account of combined action of temperature gradient and void below the slab, dynamic response characteristics of wheel-rail system has been computed and analyzed. The results show that, the temperature gradient of track slab and its warping deformation has large effect on longitudinal and horizontal tensile stress of track slab, but little effect on train body vibration, namely the driving stability, and certain effect on the rate of wheel load reduction. The effect becomes larger with higher speed and longer void length. So it is suggested that at the high-speed running region and in the season of large temperature gradient, the inspection and control of mortar void below the track slab should be strengthen.Under the action of temperature gradient, track slab tensile stress increases obviously when train passes. If the positive temperature gradient is 110℃/m, the maximum longitudinal and horizontal tensile stress of track slab is separately 4.25 and 3.14Mpa, which is closed to limit stress of slab cracking and may have adverse effect on track plate durability. If the running speed is higher, temperature gradient is larger and void below the slab is longer, the rate of wheel load reduction increases significantly, meanwhile the effect becomes larger with the void length and temperature gradient increasing. If the running speed is 350km/h, temperature gradient is 110℃/m, void length is 1.2m, the reduction rate reaches 1, which may affect the operation safety. |
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