| Rail corrugation is a kind of periodic irregularities with higher amplitudes at distinct wavelengths occurring on the running band of rail head. Rail corrugation is a significant problem for the railway industry worldwide not only raising the risk of operation safety but also increasing the cost of maintenance. Based on the available data, about 40% of all transit tracks are prone to corrugation development. There have been many studies on rail corrugation that span for more than a century, however, the mechanism of rail corrugation is still a challenging issue nowadays.Rail corrugation becomes a serious problem in certain new lines of Beijing metro. Around 20% rails suffer the damage caused by corrugation. The work presented in this dissertation is part of the projects to find the cause and solution of corrugation in Beijing metro during the years 2008-2014 and supported by Beijing Municipal Science & Technology Commission (No.Z101106000410004) and Beijing Municipal Commission of Transport. After been demonstrated, parts of the findings from the dissertation were employed to direct the treatment campaign against rail corrugation on Beijing metro.The work presented in the dissertation includes:(1) For the presented problem occurring in Beijing metro, a literature review was given in this dissertation. There reference included the research history, the division, the mechanism hypothesis, treatment solutions and the cases studies conducted by transit systems of other countries.(2) In order to characterize the profile of rail surface and quantize the growth of rail corrugation, measurement and description method of rail corrugation was discussed and confirmed, which was used for the description of the presented study of rail corrugation on Beijing metro;(3) Researches campaign were conducted to characterize the rail corrugation occurring on Beijing metro and to find out the main causes affecting on both the initially formation and development stages, included the measurement on rail profile character, the pass-by measurement on rail dynamic response, the laboratory test on static stiffness of rail support, the laboratory test on frequency responses properties of track, the laboratory test on dynamic damping properties of track, the analytic mathematical calculation on the dynamic properties of track, the FEM calculation on the dynamic properties of wheel-set, and et.cl.(4) In order to explain how the rail got corrugated from the initially uncorrugated condition, a hypothesis of corrugation mechanism on Beijing metro was raised as below: Track’s sensitivity for typical vibrations clearly appears when inventorying the response frequencies, which heavily depend on the properties of rail support structure in the range of 100-400Hz. When considering the load input, generated by traffics at the anti-resonance frequencies of wheel-sets, violent wheel/rail dynamic interaction excites dynamic loads which cause material damage (wear or plastic flow) on the contact surface, thereby modifying the initial profile. In the basic feedback loop, the same irregularities excite each train, and the damage caused by one train tends to exacerbate vibration of subsequent trains, leading to further damage at a specific wavelength, which was determined by the resonance frequency of support system under rail.(5) Based on the mechanism raised in this dissertation, two treatment solutions was proposed to control the growth of corrugation, by modifying the dynamic properties of supports under rail in one way, while increasing the decay rate of vibration along rail in the other way. After almost one year monitoring on the growth of corrugation on the test sections, both solution were demonstrated effectively inhibit corrugation initiation and reduce growth rate under corrugated condition.The presented rail corrugation problem in this dissertation was a brand new issue during the rapid development period for railway transit system in China, which are found obviously different from the corrugations found on available literatures and references over the world. The researches therefore are full of challenges and creative findings both in theory and engineering applications. Based on above research work, the creative contributions of the author in the presented dissertation are listed below:(1) Considering the dynamic stiffness of fastening system varies with frequencies, the frequency-domain analytical solution was well improved to predict the frequency response function of rail. The calculation result indicated that the typical wavelength of corrugation depend on some specific frequencies root in vibration mode of the supports.(2) Since it is the first time to attribute the typical wavelength of corrugation to the domain frequency of vibration mode of the supports under rail, the mechanism hypothesis of corrugation occurring on Beijing metro contributes to a new wavelength-fixed mechanism of corrugation.(3) Solutions were proposed and demonstrated to suppress the growth of corrugation.(4) A direct measurement method for characterizing corrugation of rail was prepared for Beijing metro, which contributes to a local standard for track maintenance against rail corrugation;... |
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