A simplified method to account for the effect of human-human interaction on the pedestrian-induced vibrations of footbridges

For the design of slender footbridges, the vibration serviceability under pedestrian excitation is often the governing criterion. In design stage, vibration levels are predicted using simplified load models that are extrapolated from single-person force models to represent the effect of a crowd. However, these load models disregard Human-Human Interaction (HHI) and Human-Structure Interaction (HSI). This contribution investigates the effect of human-human interaction on the resulting structural response. A social force model is applied to simulate the realistic pedestrian traffic. The time-varying position and velocity of each pedestrian in the crowd are transferred into the necessary inputs for detailed step-by-step simulations of the pedestrian-induced forces and the resulting pedestrian-induced vibrations. The results show that accounting for HHI results into a reduced global walking speed. Also, the inter-person variability of the step frequencies is lower than when HHI is disregarded. As an alternative to the computationally expensive social force model, the effect of HHI is translated into an equivalent distribution of step frequencies of the pedestrians in the crowd. The results show that this simplified model allows for a very good approximation of the HHI effects on the resulting crowd-induced loading and structural response.