Vibration mitigation of high-speed railway bridges : Application of damping devices in theory and practice

Abstract: The dynamic response of railway bridges is an important aspect to consider, as the repetitive loading from passing trains may result in excessive vibrations of the bridge deck. Several design criteria are developed in order to assure the structural safety and passenger comfort during train crossings of a bridge. However, bridges are usually not designed to be adaptable to future requirements or changes in the design codes, due to e.g. cost issues.Prospectively, higher speeds of trains and an increased passenger capacity could potentially mean that bridges designed according to prevailing design requirements turn obsolete. This could be particularly problematic, as the planned interconnecting routes within the European Union increases the possibility that faster and longer trains will cross the Swedish railway lines. Hence, an increased demand for innovative design solutions for new bridges and efficient upgrading methods for existing lines has emerged.The aim of the present thesis is to propose a vibration mitigation strategy that is insensitive to changes in the structural geometry or train composition. The main focus is a retrofit method with damping devices installed between the bridge superstructure and the supports, which will reduce the dynamic response of bridges subjected to passing trains. Theoretical studies, numerical simulations and experimental tests are performed and analysed to examine if the proposed retrofit systemis suitable for the present case. A proof-of-concept and a reliability study are conducted, to ensure the applicability and robustness of the proposed method. Finally, real-time hybrid simulations, laboratory tests and full-scale field experiments are conducted in order to validate the proposed vibration mitigation strategy.In theory, it is found that the damping devices efficiently reduced the response of the bridge below permitted limits. From a practical point of view, the experimental test indicates that the equivalent damping ratio of the system is increased due to the damper retrofit. However, the actual measured effect of the damping devices on the bridge deck response turns out to be lower than expected from numerical simulations. The reason for this is likely due to malfunction of the dampers, which was verified in additional laboratory tests after the field measurements. Hence, adequate damper forces were not provided at low amplitudes of vibration. Conclusively, further studies are necessary in order to validate the proposed method, but the applicability of the system still shows great potential based on the results from this research work.