ABSTRACT
Due to their lightweight, slenderness and extremely low structural damping, footbridges may often be prone to vibrations under human-induced excitation. As a consequence, structural control devices, mainly TMDs, have been installed before or after the footbridge opening to mitigate excessive vibrations under pedestrian dynamic loading. The aim of this study is to explore 729an alternative approach towards the mitigation of human-induced vertical vibrations: instead of acting on the structure, the novel approach acts on the source of excitation, that is, the crowd flow. Bearing in mind the dependence of the step frequency on the walking velocity, which in turn depends on the crowd density, a strategy based on the modification of the crowd flow along the footbridge, through the proper location of obstacles on the deck, is proposed. The crowd-based strategy can be quickly implemented, either as a permanent (e.g., benches or light poles) or an emergency temporary measure (e.g., Jersey barriers), and is expected to be cheaper than structure-based alternatives. The study is carried out by means of numerical simulations. Crowd dynamics simulations are performed through the commercial software Mass Motion, which is based on a microscopic model of crowd dynamics. The generated pedestrian trajectories and velocities are then used to build the force signals, that are subsequently applied on a 1DOF structure model to calculate the vertical response. The effectiveness of the proposed crowd-based mitigation strategy is then evaluated on an ideal footbridge and finally compared with the one of a linear viscoelastic TMD, the latter designed to meet vertical vibration serviceability requirements.
