Numerical study on the impact of random rail irregularities on the dynamic response of simple railway bridges 

This Master’s thesis addresses the effects of track irregularities on the numerical prediction of the vibration response of railway bridges. Results of numerical parameter studies are compared to design rules of the current codes. The bridge is represented by a simply supported Euler-Bernoulli beam, and different multi-body systems model the crossing high-speed train. Track imperfections are described by geometric irregularity profiles, which are generated based on the assumption of a stationary stochastic process. By applying a substructure approach, bridge, train and irregularity profiles are combined to a single model. The equations of motion of the coupled system are solved numerically. Maximum values of acceleration and deflection of the railway bridge, shown as functions of the train speed, represent the vibration response of interest. The results of the system with irregular rails are compared with the dynamic response of a bridge with perfect tracks and a statistical assessment about the influence of track irregularities is made. In contrast to a deterministic dynamic computation with perfectly smooth rails, the response considering rail irregularities can only be described by statistical parameters such as mean and standard deviation. In order to determine these statistical parameters of the vibration response, Monte Carlo simulations are conducted. A convergence analysis reveals the number of required irregularity profiles, which is a trade-off between accuracy and computational effort. Based on the obtained results, the influence of various model parameters on the maximum bridge response is studied. The power spectral density function and the range of wavelengths are varied when generating irregularity profiles. With respect to the train model, multi-body systems of different degrees of sophistication and various train types are considered. The variation of the bridge span, fundamental frequency, damping, and mass provides an overview of factors that affect the vibration response in the presence of track irregularities. On the basis of these outcomes a comparison between the aforementioned factors and the ones defined by design rules of the current code is conducted.



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