Mechanism of wake-induced vibration and mitigation in parallel box girders of coastal long-span cable-stayed bridges

Coastal long-span parallel bridges exhibit complex aerodynamic interference due to the narrow distance between two decks and high wind barriers. In wind tunnel experiments, the vibration characteristics of parallel bridges with original cross-sections are evaluated, and a novel aerodynamic countermeasure is proposed to mitigate wake-induced vibrations (WIV). A fluid-structure coupling model for parallel bridges is then constructed to analyze the WIV mechanism and the mitigation measure. The results show that when the windward bridge employs slatted wind barriers and installs continuous maintenance tracks on the lower deck, the leeward bridge encounters significant vertical and torsional WIV. Large-scale vortices generated in the wake regions of the upper and lower decks periodically shed and dissipate in the slot between the parallel bridges, forming harmonic wakes that induce significant WIV. When the maintenance tracks are on the upper deck or intermittent, and the guiding wind barrier blades are tilted downward by 10° toward the leeward bridge, the WIV amplitude can be notably reduced. The downward-tilted blades direct the flow obliquely downward, which limits vortices shedding and movement from the wake region of the windward bridge. This mitigates the formation of harmonic wake, reducing the vertical and torsional WIV of the leeward bridge.