Calibrating Pedestrian-Bridge Standards for Vibration Serviceability

Abstract

Ensuring serviceability is central to the design of pedestrian bridges (PBs); hence, their design is often governed by the serviceability limit state (SLS) under pedestrian loads. A reliability-based evaluation of various design codes and standards (collectively called guidelines), namely, ISO 1137, Eurocode 5, the British National Annex, and SÉTRA, has demonstrated a need to calibrate these guidelines for a higher reliability level to achieve a sufficient and uniform reliability index across different PBs for both the design and rare traffic loading events. This paper discusses the process and the results of calibration of these SLS design provisions for PBs. To achieve sufficiency for both design and rare events, an iterative process is introduced to estimate the desired reliability index. To achieve economic designs after the calibration process, comfort limits depending on both the frequency of traffic and the bridge class based on their routes, uses, and locations are applied during the estimation of desired reliability index and the corresponding design partial factors. This study is limited to truss-type metal PBs. A general observation from the calibration results is that the partial factors for a given reliability index are consistent across different bridge classes and guidelines, as a result of the approach adopted in this exercise. It is possible to achieve a sufficient and uniform reliability index across all bridge classes under both design and rare loading events while ensuring economic designs using frequency and class-based comfort limits. Although the desired reliability index is the same for all of the guidelines for sufficiency during the design loading event, there is significant inconsistency observed for the rare loading events. To achieve the same desired reliability index (i.e., uniformity) across guidelines, it is recommended to calibrate using the maximum desired reliability index estimated across all the guidelines for a particular event. The estimated desired reliability indices and the partial factors are sensitive to the coefficient of variation (COV) of the acceleration limit used for the SLS check.