Estimation of the changes in the dynamic parameters of a footbridge due to pedestrian flows by a human-structure interaction model

The determination of the maximum acceleration that occurs in a footbridge under the pedestrian step is a conditioning element in the design of these structures. In recent years, several procedures and pedestrian load models have been published to estimate most accurately the response of the footbridge under the different load scenarios. Normally, the numerically estimated response presents certain deviations which occur actually in the structure. One of the major shortcomings of existing models is not to consider in depth the energetic interchange that takes place between pedestrians and structures, not taking into account the change experienced by the dynamic properties of the structure due to the presence of the pedestrians. In this paper a pedestrian-structure interaction model is shown that allows considering the above effects. The mathematical development of the model is presented which includes the coupling that occurs between the dynamic parameters of the structure and the pedestrians during the walking action. The dynamic parameters of the model have been estimated from results shown currently in the international literature for passive pedestrians in stadiums. One interesting application of the interaction model is to perform an estimation of the change in the natural frequencies of the structure according to the considered pedestrian flow. In that sense, a comparative study of the experimental and numerical change of the first natural frequency of a real footbridge under controlled groups of pedestrians has been shown. The correlation between the experimental and numerical results is appropriate.