Proposal and calibration of a biodynamic model of human-structure interaction by the resolution of the inverse dynamic problem: application to pedestrian bridges

Abstract

In this thesis a biomechanical crowd-structure interaction model is proposed and further implemented in order to adequately estimate the energy exchange between pedestrians and footbridge. The proposed model focuses on both the vibrations in the vertical and lateral directions and it allows to take into account the change of the modal properties of the structure due to the presence of pedestrians, thus improving the numerical estimation of the response of the structure under pedestrian flows. It further permits to analyze in more detail the lateral lock-in phenomenon. The model involves two sub-models, namely (i) a pedestrian-structure interaction sub-model plus (ii) a crowd sub-model. The first sub-model follows from a modal projection of a two degree of freedom system that simulates the behavior of each pedestrian, on the vibration modes of the structure. The parameters of this model are estimated from the accelerations recorded on a real footbridge by implementing an inverse dynamic approach. For the second sub-model, the crowd behavior is simulated via a multi-agent method. The performance of the resulting overall model is assessed by correlating the experimental and numerical dynamic behavior of two real footbridges. In particular two phenomena are analyzed in detailed: (i) the change in the first vertical natural frequency of a real footbridge induced by the pedestrian-structure interaction and (ii) the occurrence of the lateral lock-in phenomenon due to the pedestrian action. The proposed model leads to numerical results that exhibit good agreement with the obtained experimental values. Therefore, it becomes a valuable tool to account for the change on the modal properties of a footbridge induced by the crowd-structure interaction phenomenon. The consideration of this factor allows estimating more accurately the dynamic response of the footbridge under the pedestrian action, analyzing in more detailed the occurrence of the lateral lock-in phenomenon or improving the efficiency in the design of passive and active dampers if their installation was necessary to guarantee an adequate comfort level on the footbridge