Efficient dynamic performance assessment of a footbridge

The dynamic performance of footbridges has become a significant concern in recent years, resulting in increasing demand for assessment of the performance of new and existing footbridges subject to pedestrian loading scenarios far more complex than the existing code provisions. Performance assessment typically involves predictions based on numerical simulations using finite-element representations and pedestrian load models, possibly followed by experimental assessment under normal and limiting load conditions. As dynamic performance is strongly related to all the modal parameters of the bridge, namely modal frequency, damping, shape and mass, their reliable identification for modes to be involved in pedestrian-induced response is central to assessment. The paper describes an efficient procedure for assessing dynamic characteristics and performance using a combination of visual survey, finite-element modelling and brief and unobtrusive dynamic testing, followed by short observation of pedestrian-induced response and finite-element model updating for evaluating other loading scenarios. The procedure involves minimal effort for maximum effect, generating a reliable analytical representation for response simulation and checking the serviceability of the bridge. The procedure has been tested using an existing non-problematic bridge, as described here, before being used on new structures.