| Transition section of subgrade is the weakness to interfere with smoothness of the tracks in the high-speed railway. Aimed at 350 km/h Wu-Guang passenger railway line whose design criterion is higher and requirement is more strictly, the reasonable design of transition section is the key to ensure the track safety and smoothness, and the dynamic performance research of transition section under high speed train is the important index to validate if it is designed in reason. Considering transition section appeared every 45m along the line. The research on effect between thick transition sections is the key stone and nodus in railway studies nowadays. The thesis which is supported in part as a project of National Natural Science Foundation of China (No:50678177) has studied the dynamic response characteristics of bridge-subgrade transition sections under the train load influence in Wu-Guang passenger line. The material parameters and stiffness ratio of bridge-subgrade transition section were obtained first by tests indoors and outdoors, then the dynamic performance rule of transition section was analysed to base on large-scale train tests in Wu-Guang passenger line.Introducing wheel-rail force established mathematically by rail acceleration, finite element analysis model of the track-subgrade was established by using ANSYS Parametric Design Language (APDL). In addition, extracting rail model parameters from finite model, vehicle-track-subgrade model were established by mode superposition method using FORTRAN language, and influential factors of dynamic performance of transition section and the influences between thick transition sections were analysed. The main research work of this dissertation can be summarized as follows.(1) Some problems and processing methods about transition section at home and abroad were analysed, The research history and development of track/subgrade dynamic response were reviewed, the problems existed were put forward.(2) Dynamic parameters and physical-mechanical parameters of subgrade were obtained by tests such as wave-velocity experiment, large vibration-exciting experiment and coarse-grain physico-mechanical tests. And stiffness ratio of bridge- transition section was obtained by synthetical stiffness method, the rational test schemes for getting the subgrade pamameters were put forward by comparing results from diffirent testing.(3) Based on variational (or weak) form of the equilibrium equations for the ballastless track-roadbed system in Galerkin method and total Lagrangian form, started to researched constitutive model, material damping model, element chosing for CA motar, various finite element coupling, and introducing visco-elastic artificial boundary, make the best of measured rail acceleration, then wheel-rail force were calculated by mathematical method such as Fourier transform. Finally, a semi-infinite tri-dimensional spatial timing coupled dynamic model has been improved and founded. The global matrices equations have been solved by implicit time integration of Newmark. Owing to many restricted equations being existed in the dynamic model, frontal solution is adapted to modal analysis, and reduced solution is adopted for transient dynamic analysis.(4) Extracting modal shape and frequency from finite element model, finite element method and mode superposition method were used to establish vehicle-track-subgrade model by FORTRAN program. It reduces the matrix dimentions of vechile-rail coupling equation and enhances computing speed. The result shows that the model is feasible and universal for analyzing dynamic performance in spatial structure details.(5) In-situ maesurements are performed on Wu-Guang passenger railway. During the tests, the train speed reaches to 354.7km/h, the dynamic responses under high-speed train load are obtained first. Introduced the wavelet analysis theory,on the basis of Newton-Cotes integration method,five-spot triple smoothing method,the real time-history curves were obtained with Matlab programs. In order to get the mean square value, mean value and variance of the response magnitude, the time-history curves were analysed statisticly and were hypotheses detected by K-test. Then the relationship between longitudinal distance,depth and dynamic response under different train speed were analysed.Some parameters are investigated which affect dynamic response of the system by utilizing this model, such as the axial load,train speeds, the train moving directions. The dynamic design-control conditions and dynamic analyse-control standard of transition section subgrade and some suggestions of designing transition section were put forward.(6) According to the track-rail dynamic performance evaluation index at home and abroad,the dynamic response of the vehicale, rail and roadbed were obtained by the established model in chater four and chapter five.Based on design parameters of roadbed in Wu-Guang passenger line, some parameters which affect dynamic response of the system were analysed, such as length of transition secion, differential settlement, the rigidity and the type of transition section and the corresponding reference value were put forward.(7) Dynamic performance of different spaces between two bridge-transition sections were analysed by mean of the rail-subgrade model of finite element and the vehicale-rail-subgrade model of FORTRAN language. It was compared with the dynamic performance of the real bridge-transition section and the evaluation criterion existing, and the better favorable space between two bridge-transition sections was obtained. Then the ultimate limit conditions were supposed to considering for calculating the dynamic performance of the transition section. Furtherly the different results were researched between "one transition" and "two transitions". The result shows that "one transition" is the rational disposal route for closely spaced transition section with the better favorable space.
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