Retrofitting of Existing Railway Bridges for Increasing Speed of Trains

Abstract

There is a growing demand for increasing the train speed in India, as well as in rest of the world. However, when the train speed exceeds a certain threshold, there is a greater likelihood of resonance occurring between the forcing frequency of train movement and the natural frequencies of the bridge. This resonance leads to an increase in the dynamic response of the bridge. Dynamic analysis is crucial for understanding the dynamic behaviour of the bridges near to resonating speed. This dissertation investigates retrofitting of four standard Research Designs and Standards Organization (RDSO) railway bridges, including two composite and two truss bridges, considering the increased speed of Vande-Bharat trains up to 200 km/h. As retrofitting heavily relies on accurate dynamic analysis, the initial part of the study focuses on dynamic analysis. A sensitivity analysis is conducted on a simple beam and a complete 3D bridge structure to determine the optimal parameters for a reliable analysis, including integration time step, analysis type (modal or direct integration), and element size in the FE model. Additionally, an analytical solution is presented, idealizing the bridge as a simply supported beam, and the train load as a series of moving point loads, to verify the numerical results of the sensitivity analysis. Upon comparing the Dynamic Amplification Factor (DAF) obtained from the dynamic analysis with the CDA specified in the Indian code, it is concluded that the considered dynamic forces are sufficient from a bridge safety perspective up to the targeted speed of 200 kmph for Vande-Bharat train loading. However, it is observed that the vertical acceleration exceeds the specified limit, raising concerns about the train’s serviceability and operational safety. Therefore, retrofitting measures are necessary to mitigate the vertical deck acceleration. Retrofitting of the considered bridges using Tuned Mass Damper (TMD), Multiple Tuned Mass Damper (MTMD), and Fluid Viscous Damper (FVD) is explored. Parametric studies are performed to obtain optimal parameters of different dampers that successfully bring the response of the considered bridges below the prescribed limit.