Vertical Crowd–Structure Interaction Model to Analyze the Change of the Modal Properties of a Footbridge

Abstract

In this paper, a biomechanical crowd–structure interaction model is proposed and further implemented to adequately estimate the energy exchange between pedestrians and a footbridge. The proposed model focuses on the vibrations in the vertical direction, and it allows for taking into account the change of the modal properties of the structure due to the presence of the pedestrians, thus improving the numerical estimation of the response of the structure under pedestrian flows. The model involves two submodels, namely (1) a pedestrian–structure interaction submodel and (2) a crowd submodel. The first submodel follows from a modal projection of a system with two degrees of freedom, which simulates the behavior of each pedestrian, on the vibration modes of the structure. The parameters of this model have been estimated from the accelerations recorded on a real footbridge. For the second submodel, the crowd behavior is simulated via a multiagent method. The performance of the resulting overall model is assessed by correlating the experimental and numerical dynamic of a real footbridge under a group of pedestrians at different controlled step frequencies. In particular, the change in the first natural frequency induced by the pedestrian–footbridge interaction is discussed in detail. The proposed model leads to numerical results that exhibit good agreement with the recorded experimental values. Therefore, it becomes a valuable tool for estimating the change on the modal properties of a footbridge induced by the crowd–structure interaction phenomenon.