The Effect of Clusters within Crowds of Pedestrians on the Vertical Response of a Flexible Footbridge

The issue of excessive vibrations of footbridges due to the passage of pedestrians has been well documented in the past decade. Despite this there still remains great uncertainty as to how to predict the acceleration response of a footbridge due to crowd loading. This paper investigates the vibration response of a flexible footbridge subjected to crowd loading. Using a statistical model which caters for the variability of pedestrians, the vibration response of the footbridge is obtained. In this work, the effect of social groups or clusters of pedestrians in a crowd is investigated. Herein a cluster is defined as two or more pedestrians walking together with the same velocity. The predictions of this model are compared to a model which uses only lone pedestrians walking within a crowd. None of the current design codes or guidelines considers the possibility of pedestrians walking together. The size of the clusters is found in literature to follow a Poisson distribution. In this paper variations of the probability of clusters appearing in the crowd are assessed. It is found that the response of a crowd with clusters present is similar to the predictions of the UK National Annex to Eurocode 1.