Research On U-Girder System Structure Subjected To Force In Urban Rail Transit

U-girder system is a new product, which evolved from groove-girder in urban rail transit. With the support of Nanjing Metro Group Co., Ltd. and Chongqing Rail Transportation (Group) Co., Ltd., Beijing Urban Construction Design Research Institute cooperated with some domestic scientific research institutions, after several years of repeated design research, computational analysis and experimental research, developed and had independent intellectual property rights of U-girder system. The system has been applied in Chongqing City Metro Line Project. U-girder system has advantages of conducive to environmental protection, good adaptability to architecture landscape, whole life construction, low-cost operation, and highly efficient system integration. As U-girder structure significantly different from the traditional box-girder and T-girder, in terms of static stiffness, crack resistance, ultimate bearing capacity, structural safety and durability, and dynamic vehicle-bridge interaction and environmental vibration impact, the study of U-girder system fills the gaps of the research field in our country. Summarized and absorbed the previous study of U-girder system, based on the first application of U-girder system in urban rail transit, this thesis mainly conducted a study of the following areas:1. It’s the first time in our country to do the tests of U-girder structure static load and fatigue load for6million times. Static load tests includes:the largest cross-sectional load, the maximum shear load near bearing cross section,1.2times of design bending moment under the action of crack resistance, part load of cross bridge board, ultimate flexural strength test of bridge construct under2.5times of the design load. Fatigue load tests includes:6million times of transverse fatigue load test, and shear, bending, cracking and damage to performance tests under6million times of fatigue experiments. Based on the research results in the tests, the corresponding design and construction recommendations were proposed for later projects.2. In terms of the special structure of U-girder rail transit system, ANSYS (a large-scale general-purpose finite element program) was used to establish a spatial analysis model. Considering the issue of U-girder shear lag effect and the structure sensitivity, the study focused on the structure and load ways of U-girder by numerical simulation and influencing factors analysis.3. According to the theory of vehicle dynamics, a rail vehicle dynamics model with31DOFs (degrees of freedom) was established by using the equation of Lagrange. Then, based on the principle of Hamilton in discrete systems, the finite element expressions of U-girder structure dynamic equations were derived. Learn from previous study results of U-girder rail transit system, the detailed derivation and simulation was elaborated on excitation source, wheel-rail contact geometry and contact mechanics. In terms of the wheel-rail contact geometry, a space model of vehicle-bridge coupling vibration was established through the link between vehicle and bridge subsystems. A method of static and dynamic stiffness combined was taken to write numerical computer program for the large system of vehicle-bridge coupling vibration.4. A standard span of30m single line U-shaped structure, which is in the elevated section of Chongqing City Metro Line Project, was taken as the study object to have a comprehensive research and comparative analysis on vehicle-bridge dynamic response in U-girder rail transit system. The study involved train speed, bridge structure parameters, locomotives structural parameters, track irregularity, random vibration and so on. Two-pronged approach to structure sensitivity in time domain and analysis of frequency domain random vibration (PSD) were taken by the self-compiled computer program.5. As an example of U-girder applied in Chongqing City Metro Line Project, this study explored the impact on the surrounding environment of dynamic response of U-girder in vehicle-bridge system for urban rail transit, the vibrating dissemination caused by vehicle-bridge coupled vibration in the soil, and the vibrating impact on the surrounding buildings. In the course of the study, drawing on previous research experience, the vehicle-bridge environmental vibration system is divided into two subsystems, include the vehicle-bridge coupled vibration program compiled from programming software FORTRAN, and three-dimensional model involved bridge foundation, soil, surrounding buildings, which established by finite element program ANSYS. The process of study is first to take the results of derived from vehicle-bridge coupling deduced horizontal, vertical force, which extracted from the self-compiled program, as an external excitation applied to the model involved bridge foundation, soil, surrounding buildings; then to analyses the vibration response of surrounding soil and buildings, under the effect of different factors.