Evaluation of Design Provisions for Pedestrian Bridges Using a Structural Reliability Framework

Abstract

The design of pedestrian bridges (PBs) is typically governed by the serviceability limit state under human-induced excitation. A comprehensive evaluation of the reliability level achieved in designing for this limit state has not yet been reported. This paper attempts to address this gap for metal structures through a comprehensive structural reliability-based evaluation of design guidelines currently used in North America and Europe. An advanced first-order second-moment (AFOSM) method is used to determine reliability levels under different loading scenarios considering uncertainties in the pedestrian-induced walking loads, structural properties, and comfort limits. The results show that the guidelines do not achieve sufficiency under the design traffic. Moreover, suburban or urban PBs with frequently occurring design traffic densities of 0.2–0.8 pedestrians per square meter achieve very low reliability levels under infrequent traffic densities. Significant disagreement in the reliability levels obtained by the different guidelines is observed. Based on this evaluation, it is proposed that current design provisions be calibrated to a higher reliability index under design crowd densities and that traffic-dependent comfort limits be adopted. The reliability level achieved by incorporating a model error term, previously proposed by the authors to better align model predictions with observations, is also evaluated. The key results from this evaluation show that the uncertainty in the model error term has a positive impact on the reliability estimates; thus, this term can be regarded as deterministic.