Modelling of self-excited vertical forces on structures due to walking pedestrians

Although many models of pedestrian dynamic loading have been proposed, possible bi-directional interactions between the exciter and the excited structure are generally ignored, particularly for vertical vibrations. This shortcoming has arisen from scarcity of data on gait adaptation strategies used in the presence of structural motion and, as a consequence, the absence of a credible fundamental pedestrian model capable of capturing the underlying relations between the two dynamic systems. To address this inadequacy of current approaches, a biomechanically-inspired inverted pendulum pedestrian model has been applied to the human-structure interaction problem. The behaviour of the model is studied when subjected to vertical motion of the supporting structure, in particular in relation to potential self-excited forces that can be generated. A mechanism has been identified by which the timing of pedestrian footsteps can be altered subtly, giving a net damping effect on the structure without necessarily involving full synchronisation. It has been found that, depending on the ratio between the bridge vibration frequency and pedestrian pacing frequency, the walkers can effectively act as positive or negative dampers to the structural motion, but it is expected that for a group of pedestrians with distributed parameters their action is on average to add damping and mass.