Experimental Evaluation of Synchronisation in Footbridges due to Crowd Density

Synchronisation of movements of pedestrians implies a significant increase of the applied loads, and this has been appointed as the cause of excessive vibration in some footbridges. Experimental results on this phenomenon are scarce to support the development of design load models. Two aspects have been appointed as related to the phenomenon of synchronisation: interaction between pedestrians and structure (lock-in effect) and densification. In this paper, an experimental investigation of the potential synchronisation among pedestrians while walking across a prototype footbridge is presented, focusing on the contribution of densification. An additional walking test in a 25 m long corridor was included to evaluate the effect of the path length. In the footbridge, three tests with different pedestrian densities were carried out. The tests were filmed by a video camera and the processing of the images enabled the phase differences among the movement of pedestrians to be determined in both vertical and lateral (transverse) directions, by capturing the lateral movement of each pedestrian's head. The pacing rates of pedestrians walking in groups of varied densities were also determined. Synchronisation was not observed in spontaneous walking in either of the analysed directions (vertical and lateral) for densities up to 0,9 pedestrians/m². The results presented may be useful for the development of crowd load models for footbridges. However, further tests with higher densities and, ideally, longer pedestrian paths would be necessary to completely clarify the phenomenon.