Research On Stiffness Of Long-Span Railway Suspension Bridge

Determination of stiffness parameters is very important in the design of long-span bridges. Although the regulations of limit values such as the ratio of deflection to span in design codes have considered the theory of vehicle-bridge coupling vibration, they are just based on dynamic analysis and practical test of medium and small span bridges, and they aren't suitable to long span bridges. At the same time, there are few railway suspension bridges for reference, even there is no any pure-railway suspension bridge built so far, it's difficult to design similar bridges. Taking a long-span railway suspension bridge as an example, a detailed research on its stiffness parameters and index systems of stiffness for long-span railway suspension bridge is made in this thesis.Firstly, based on the theories of finite element method, a whole dynamic model of the long-span railway suspension bridge is established and an applicable simplification method for plate-truss beam is presented. The simplification method can improve calculation efficiency without loss in accuracy. Model analysis of the bridge is carried out by two programs and it provides calculation model and relevant parameters for further research.Then, index systems for the vehicle and bridge based on train running performance are summarized. According to relevant research and actual engineering examples, the safety, comfort index of the vehicle and stiffness limit of the bridge adopted in this thesis is presented.Furthermore, an equivalent two-dimensional model for plate-truss bridge deck is presented to simulate aerodynamic characteristics by computational fluid dynamics(CFD). And based on the theories of CFD, three aerostatic coefficients of the bridge deck at different wind speeds and attack angles are calculated. According to the requirement of further calculation, this paper uses UDF technique to obtain the flutter derivatives of the bridge deck at different wind speeds based on forced vibration method.Finally, from the point of view of dynamic characteristic analysis, vehicle-bridge coupled vibration analysis, aerostatic effects, buffeting responses, a detailed research on the effects of stiffness parameters such as girder height, beam width, the ratio of dead load to live load, stiffness of pylon tower and main cable on static and dynamic response of the bridge is made under multiple loading conditions, and partial stiffness limits of the bridge are discussed according to the calculation results. The results show that there are differences in influence degree of different stiffness parameters on each static and dynamic response, unreasonable stiffness parameters might weaken durability of bridges and comfort properties for vehicle moving on bridge, and even lead to accidents. According to the calculation results, partial stiffness limits of long-span railway suspension bridge are presented to provide reference for bridge design.