The Influence Analysis Of The Sleepers Of Ballast Track Bridge On Track Dynamic Response

Sleepers, as one of the main components of track, bears the pressure from rails andelastically transmits it to ballast covering, and displays the functions of connecting the railsand covering as well as keeping the geometric shape of tracks. As the speed of trainsaccelerates, the vibratory rate will increase accordingly, thus, greatly strengthen the vibratoryload of the trains on tracks which further causes the decrease of frictional resistance amongballasts, the acceleration of rockslide, and the fastening of line transformation and theaggravation of track conditions, even will cause the liquidation of ballasts, therefore, canhardly maintain the geometric shape of tracks. Therefore, voided phenomenon of sleepers willbe formed as there is no contact among sleepers, ballast coverings and bridge. It is theexistence of such voided phenomenon that would cause horizontal or vertical off-limitacceleration of trains, especially high-speed trains, thus, forming sway car phenomenon. Thisdissertation will firstly compute wheel-rail contact force via establishing the model ofvehicle-track-bridge coupling system, and then establish the model of track-bridge verticalcoupling system in Ansys in order to analyze the dynamic responses of trains of these twosystems under normal condition andvoided condition respectively. Furthermore, acomparative analysis of dynamic responses caused by different voided sleepers’ quantity anddifferent voided distribution will be made in the hope of providing theoretical data forpermanent way maintenance. Specific research aspects and the results are as follows:(1) The computation of the wheel-rail contact force of the vehicles-track-bridge verticalcoupling system. According to traits of vehicles-track-bridge vertical coupling system, and inusing finite-element method and Larange equation, new vehicle element and track elementthat are appropriate for analysis will be put forward, thus respectively to establish thedynamic analysis models of vehicles-track-bridge systems, as well as to deduce stiffnessmatrix, mass matrix and damping matrix of vehicle element, track element and bridge elementrespectively. During this process, the whole vehicles-track-bridge coupling system only needsto diverge into vehicle element, track element and bridge element, among which thetrack-bridge system diverges into a three-layer beam element while each vehicle diverges intoone vehicle element. The stiffness matrix, mass matrix and damping matrix only needs to be formed once in calculation, and then to be organized to form total stiffness matrix, total massmatrix and total damping matrix that would be enough for calculations in every later step.Corresponding computing software for the dynamic analysis model of the establishedvehicles-track-bridge coupling system is programmed via using Matlab software. Calculatingthe wheel-rail contact forces under different speeds, the result shows that the higher the speedis, the greater the vibration of the contact force will be, but all fluctuates around the gross railload on axle.(2) Applying Ansys software to establish the model of track-bridge vertical couplingsystem and then to direct the wheel-rail contact force into Ansys to compute and analyze thedynamic responses under normal condition and voided condition respectively. The resultsshows that: the vibratory response of the whole track-bridge system is mainly from rails andsleepers, the vibration of the bridge is so weak that it can be ignored; within normalcircumstances, the displacement and the acceleration of the rails are the most obvious underthe influence of irregularity excitation. As the wheel speed increases, little influence will beon the displacement of rails while its influence on the acceleration of rails is obviouslyincreased; however, the overall response of sleepers is only one-third of the rails;(3) To simulate sleepers voided phenomenon via deleting the damper spring betweensleepers and bridge in the corresponding position of the track-bridge vertical coupling systemmodel, and to analyze the influence of different voided conditions upon dynamic responses,then to make a comparative analysis of system responses under different voided sleepersquantity and different voided distributions, the results show that: the influence of dynamicresponses caused by voided sleepers on track system is mainly concentrated on threeneighboring sleepers near the voided position, other sleepers are prone to be normal. Voidedpositions caused by different track conditions will make a difference in the vertical dynamicresponses of rails, whose responses will be greater than under normal condition. The more thevoided sleepers, the greater the vertical dynamic responses of the track system will be,especially when continuous sleepers are voided, the response of the track will be moreobvious. Meanwhile, as the speed increases, dynamic responses of track system will be moredistinct under the influence of voided condition.