Human-Induced Vibrations of Footbridges: The Effect of Vertical Human-Structure Interaction

Slender and lightweight structures are often unduly responsive to human excitation. The concerns of vibration comfort and safety are strengthened by unexplored human-structure interaction (HSI) phenomena. The present contribution proposes a numerical model for pedestrian excitation including HSI. In addition to the well-known forces induced by a pedestrian on a rigid floor, the pedestrian is represented by a linear mechanical model to simulate the interaction with the supporting structure. Inspired by the body postures assumed during the walking cycle, the mechanical properties are chosen to represent the dynamic behaviour of the human body with one or two legs slightly bent. The effect of HSI on the structural response is evaluated for various footbridge parameters and pedestrian densities. It is shown that by taking into account HSI, the structural response is reduced. Furthermore, it is demonstrated that the unrealistic high acceleration levels as predicted by simplified force models are not reached as the result of HSI. It is concluded that the mechanical interaction with the crowd is relevant for the vertical low-frequency dynamic behaviour of footbridges.