Assessment of Lateral Vibrations of Footbridges Using a Frequency Domain Approach

Abstract

Lateral vibrations of footbridges caused by the passage of pedestrian crowds have been the object of many studies over the last decade. However, the connection between experimental and analytical results remains tenuous and as a consequence, a common set of design criteria havenot been established yet.Regarding the particular features of both the pedestrian load and the dynamic system (slender footbridges with little damping), the frequency domain analysis is a method especially efficient to evaluate the lateral response. Hence, the object of this study is to develop a general formulation, using a frequency domain approach, for assessing the lateral vibrations of any footbridge; considering the action of a crowd of pedestrians walking randomly with different frequencies. The effects of pedestrians in a swaying deck are not limited to imposing external loads; the people-structure interaction generates additional harmonics in the natural frequencies of the structure that are independent of the pedestrian frequency. Hence, human-structure phase synchronization is not a necessary condition for the development of the resonant component. The study states thatit is accurate enough to calculate the structural response using only the resonant contribution.These considerations lead to a very simple formulation that permits to establish a positive relationship between the amplification of the response and the number of pedestrians.