Aeroelastic Response of Long-Span Bridges to Downburst Wind Fields: A Nonlinear Time-Domain Investigation

In recent years, extreme atmospheric events such as downbursts have been increasing in both strength and frequency. Considering their interaction with long-span bridges, these phenomena are characterized by significant spatial and temporal variations of the angle of attack along the bridge deck, which can strongly affect the aeroelastic response of the structure. The objective of this study is to investigate the aeroelastic response of long-span suspension bridges to the passage of a downburst. The three-dimensional mean wind field is generated by superimposing a simplified analytical stationary downburst model onto an environmental stationary turbulent wind field. The resulting wind field can therefore be represented as the sum of a low-frequency component and high-frequency fluctuations characterized by time-varying statistical properties. The structural response is evaluated using a nonlinear time-domain approach, in which the effects of the low-frequency wind field are modeled through quasi-steady theory, while the influence of high-frequency turbulence is considered using a time-varying linearized approach around the quasi-steady solution. This methodology enables the capture of nonlinear effects associated with low-frequency variations in the angle of attack caused by the downburst and allows comparison with approaches assuming stationary and ergodic wind fields. Different wind scenarios are generated to analyze the influence of downburst size, position relative to the bridge, and translation speed. Furthermore, several long-span bridges with varying structural and aerodynamic characteristics are examined to assess the sensitivity of these properties to downburst-induced loads.