Interactive horizontal load model for pedestrians crossing footbridges

Abstract

In recent years several theories have been put forward in relation to lateral forces imparted on bridges from crowd movements. It is now widely accepted that the interaction between the crowd and the structure, particularly when the crowd pacing frequency is close to the lateral natural frequency, is the major factor determining the lateral response. However, very little work has been done with individual pedestrians in order to determine the relationship between the lateral force induced by a single pedestrian and the structural response. Equally, most literature concerning lateral forces induced from walking is based on results from fixed force plate tests and hence no assessment of any interaction is made. This paper examines the lateral response of a GRP (glass-fibre reinforced polymer) cable-stayed footbridge to individual pedestrian crossings at a range of pacing frequencies. Two lateral load modelling approaches are considered. The first approach, derived from back analysis of the measured bridge response, was found to be ineffective in predicting the measured response accurately. A second modelling approach, incorporating a spring-damper to represent a moving pedestrian, which thereby accounts for the interaction between the structural response and the mass, stiffness and damping characteristics of the body of the traversing pedestrian, is demonstrated to be more effective in simulating the bridge response.