The impact of vertical human-structure interaction on the response of footbridges to pedestrian excitation

Abstract

In the present paper, a detailed crowd model is applied to investigate the impact of vertical human-structure interaction (HSI) on the dynamic response of footbridges to pedestrian excitation. Assuming that the walking behaviour of the pedestrian is not affected by the motion of the supporting structure, the contact force between the pedestrian and the supporting structure is decomposed into the force exerted by the pedestrian on a perfectly rigid floor and an interaction term determined by the mechanical interaction between the person and the structure. The model is also used to evaluate the impact of various simplifying assumptions and inter- and intra-person variabilities.The results show that for the low-frequency dynamic behaviour of footbridges (<6Hz), HSI leads to an effective damping ratio which is (significantly) higher than the inherent damping ratio of the empty structure. In addition, it is demonstrated that the detailed moving crowd model can be well approximated by a time-invariant crowd-structure model. Furthermore, the influence of inter- and intra-person variability in step frequency is observed to decrease as the impact of HSI increases. Finally, it is shown that in many cases accounting for HSI leads to a significant reduction in the response of footbridges to pedestrian excitation which may be considered in practical design.