Risk-targeted design wind speeds for multi-level aerodynamic performances of long-span bridges: A real data-informed case study

Abstract

Most current bridge wind-resistant design standards adopt “uniform hazard” basis, ensuring the resistance exceeds design wind speed at a given return period. However, wind-induced failure probabilities for bridge structures, especially accounting for multi-level performances, are ambiguous, leading to significant differences in risk levels. To achieve the controllability and consistency in aerodynamic performances of long-span bridges, this study introduces the “uniform risk” into bridge wind engineering to determine the risk-targeted design wind speeds. Four performance objectives (occupant comfort, operational, continuous occupancy and instability), associated with the annual failure probability, are summarized. A case study is performed for Xihoumen Bridge by developing fragility curves corresponding to different vibration thresholds. Buffeting-related fragility curves are derived through a data-driven random model based on long-term measurements, while flutter fragility curve is obtained by Monte Carlo simulations incorporating various uncertainties. By combining with the wind hazard curves, failure probabilities for multi-level performances are estimated. Risk-targeted design wind speeds are calculated through the risk integral method, and the annual failure probabilities for code-recommended versus risk-targeted flutter design speeds are compared. Results indicate that Xihoumen Bridge has excessive wind resistance for the continuous occupancy and instability, while the annual failure risk for occupant comfort is relatively high. The code-recommended design wind speed falls short of ensuring multi-level performance objectives, whereas the risk-targeted design wind speeds effectively meet these criteria. This study provides a forward step in bridge wind engineering to develop the “uniform risk” design basis, serving the uptake of performance-based wind engineering design.