Vibration mitigation of footbridges: case studies

The paper focuses on the application of passive devices to mitigate vibrations induced by pedestrians. Three case studies are discussed, two referring to footbridges in Portugal where tuned mass dampers (TMDs) were installed to attenuate the lateral and vertical pedestrian vibrations, and the latter referring to a footbridge in UK where viscous dampers were installed to mitigate vertical vibrations. The observation of the structures before installation of these devices enables an accurate characterisation of their dynamic properties. The subsequent testing upon installation of the mechanical devices allows an assessment of their efficiency. It is observed that hardly can TMDs be perfectly tuned with the structure and that the transient character of the activation/ de-activation of TMDs contributes to a lesser than expected efficiency in the mitigation of vibrations, although the frequency range of the mitigated vibration is larger than theoretically defined. It is also shown that viscous dampers can provide a very simple and effective mitigation system.

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