Evaluation of Design Guidelines for the Serviceability Assessment of Aluminum Pedestrian Bridges

Abstract

Serviceability issues related to lightweight pedestrian bridges have attracted a great deal of attention in the literature since the London Millennium Bridge incident, which involved large amplitude motions during its inauguration. Various design recommendations have since been proposed to quantify the steady-state resonant response and to mitigate excessive levels of vibration in slender pedestrian bridges. In the current study, design provisions currently used in North America and Europe are evaluated. Two full-scale aluminum pedestrian bridges were tested in the laboratory, and their performance in terms of meeting serviceability limits under pedestrian walking loads was assessed in accordance with a number of guidelines and standards. The experiments involved walking tests under different pedestrian densities. The results show significant differences in the predicted responses, which are mainly attributable to differences in the DLFs adopted in the guidelines, lack of guidance on the appropriate walking speeds in crowd loading conditions, and the factor scaling the individual pedestrian load to multiple pedestrians. The results after applying the guidelines were found unconservative in the lateral direction. The simulated results showed sensitivity to changes in the natural frequency due to the added mass of pedestrians, which becomes especially important in lightweight bridges. Recommendations to address these issues and to reconcile the differences between the various guidelines and standards and with measurements, based on results already available in the literature, are proposed.