Simulation of human induced vibration of a lively footbridge

Abstract

In the last years, the need for structures able to link the functional and aesthetic role has led to the design of new flexible footbridges. The low ratio between permanent and variable loads makes them more sensitive to dynamic loads, such as the forces transmitted by pedestrians. During the human walking, the pedestrian moves on a flexible structure adapting his gait to the bridge motion. The interaction between pedestrian and footbridge takes place at contact points, where the pedestrian transmits contact forces to the bridge that, in turn, imposes a set of displacements and velocities to the pedestrian’s feet. The description of the human being as a mechanical system allows for the derivation of the equation of motion of the bridge-pedestrian coupled system. In this work a previously developed bipedal pedestrian mass-spring-damper (MSD) model is adopted. The analytical formulation of the human-structure interaction, involving the derivation of the bridge-pedestrian coupled equations of motion, has been implemented in a numerical code, named INTER2.0. The bridge is modelled using a commercial FE code and its geometry is fully described. The code reads in input both the bridge structural matrices and the pedestrian dynamic properties needed to assembly the MSD matrices or the feet forces. The present contribution investigates the effect, on a lively footbridge response, of a few parameters: distance between pedestrians and pedestrians’ trajectory. The results due to groups of pedestrians walking along different eccentric trajectories have highlighted the relation between the bridge mode excited and the pedestrians’ position. As it was expected, the eccentric transit induces a torsional behavior. In addition, the spatial distribution affects the bridge response: the vertical accelerations rise if the longitudinal distance among pedestrians increases, although this trend is not linear with the distance.