The Response of a Footbridge to Pedestrians Carrying Additional Mass

Footbridges with low natural frequency are susceptible to excessive vibration serviceability problems if the pedestrian pacing frequency matches the bridge natural frequency. Much research has been done into describing the response of a footbridge to single pedestrian loading. However, many pedestrians carry additional mass such as shopping bags and backpacks, and this has generally not been accounted for in previous research. This work examines this problem using an experimental bridge excited with many single pedestrian events, both with and without additional mass. The vertical acceleration response is measured and compared to moving force, moving mass, and moving spring-mass-damper models. The influence of the additional mass on the results is assessed. It is shown that current theoretical models do not provide an accurate description of the walking forces applied by a pedestrian traversing an excessively vibrating structure. When a pedestrian carries additional mass the response of the footbridge increases however the theoretical models overestimate this increase.