Key Findings from Serviceability Studies on Aluminum Footbridges

Due to their light weight and low intrinsic damping, aluminum footbridges under human-induced excitations are susceptible to excessive vibrations, which may result in serviceability failures. In general, the design provisions for the serviceability of such lively footbridges employ a basic moving load model representing a single pedestrian walking and simulate the crowd-induced vibration of footbridges from the single pedestrian load model through multiplication factors. Despite being adopted into most codes and guidelines, there is still a need for experimental investigations to understand and validate the performance of these design load models. To this end, a comprehensive experimental program was undertaken by the authors on three full-scale aluminum footbridges, both in the field and in the laboratory. These bridges were instrumented and subjected to a range of modal and pedestrian walking tests of varying traffic sizes. The comparison results between the predicted and measured responses show that commonly employed load models can sometimes be un-conservative. Recommendations are proposed to harmonize various design provisions and with measurements based on results already available in the literature. Additionally, the guidelines are evaluated in a reliability-based framework to incorporate the potential uncertainties associated with the walking loads, structural properties, and occupant comfort limits. The key results point towards calibrating the current design provisions to a higher reliability index under the design events in order to achieve sufficiency under the non-frequent loading conditions. The study also suggests adopting traffic dependent comfort limits for economic designs.

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