Experimental Characterization of Downburst Wind Loads on Bridge Decks

For long-span bridges, wind is among the most critical loads influencing design. While conventional bridge aerodynamics has largely focused on synoptic wind conditions associated with large-scale weather systems, increasing attention is being directed toward non-synoptic wind events such as downbursts. Downbursts, characterized by intense localized outflows generated by convective storms, have in recent years been observed to cause significant responses on long-span bridges, motivating further studies to understand their influence. This study presents results from wind-tunnel experiments conducted at the WindEEE Dome, where transient downburst-like flows were applied to a bridge section model at a geometric scale of 1:100. Two types of tests were performed: (i) a static pressure model instrumented with pressure taps to capture distributed load fields, including spanwise correlations; and (ii) a dynamic mass–spring section model with three degrees of freedom to measure responses induced by non-stationary aerodynamic loads. Each downburst event was repeated eight times under varying test configurations, including different bridge heights above ground and lateral offsets between the downburst centre and the bridge deck. We examine the repeatability of the experiments and characterize the pressure loads in terms of the downburst front build-up and subsequent turbulent phase. Based on these results, simple non-stationary load models using time-varying mean wind velocities and turbulence intensities are proposed for simulating downburst-induced responses of super-long-span bridges. The findings contribute to ongoing efforts to integrate non-synoptic wind effects into bridge design practice.