Pedestrian-pedestrian interaction and its effects on vibration serviceability

To this day, excessive response of structures subjected to pedestrian loading has been attributed to two separate phenomena: pedestrian-structure interaction (PSI) and pedestrian-pedestrian interaction (PPI). Whilst the former has been widely researched in the wake of the London Millennium Bridge failure, there is little empirical data on the latter in the context of vibration serviceability. This is due to significant logistical and financial challenges associated with full-scale crowd testing, and the uncertainties related to human studies. To this end, this study provides baseline information on walkers’ ability to coordinate their gait with auditory stimuli, gives some of the first evidence of spontaneous PPI in walking groups, and assess its subsequent effects on the structural response of a simulated footbridge. The magnitude of PPI was quantified using the bivariate phase difference analysis framework, based on Shannon entropy of the gait cycle time series. Furthermore, to alleviate some of the limitations of real-word crowd testing, a novel virtual reality (VR) platform was developed and validated. The platform provides a highly controlled environment for PPI testing and allows the implementation of repeatable experimental protocols whilst collecting data on pedestrian behaviour in real-time. The study describes fundamental gait parameters during solitary, overground walking, as well as insights into modes of gait coordination when subjected to repetitive auditory cues. During group walking, it was found that the overall PPI is rather weak, substantially below the levels previously reported for walking in pairs, and it strongly depends on a group’s walking speed. Numerical simulations showed that the PPI phenomenon only affects the structural response when the group’s pacing frequency is compatible with the structure’s natural frequency. The VR platform yielded qualitatively compatible results with the real-word setting for walking in pairs; however, some quantitative differences were found in terms of PPI magnitude and its directionality.