A novel strategy for mitigating the vortex-induced vibration of long-span bridges by using flexible membranes

The structural damping of a long-span bridge girder after completion is difficult to predict accurately in the design stage, and could be obviously lower than the value suggested by the code of wind-resistance design, which could lead to large-amplitude vortex-induced vibration (VIV) of the girder after completion. To address this problem, proposed here is a novel VIV mitigation strategy for a long-span bridge: in the design stage, aerodynamic design involving VIV of the girder is conducted based on the normal structural damping suggested by the design code, and flexible membranes (FMs) are designed for emergency VIV mitigation of the girder in case of very low structural damping after completion; if the girder experience large-amplitude VIV after completion because of very low structural damping, then the pre-designed FMs are used as a temporary emergency aerodynamic measure for fast VIV mitigation, providing a transition period until permanent measures (such as mechanical dampers, or aerodynamic measures) are implemented. To investigate the feasibility of this strategy, a case study was conducted involving a series of wind tunnel tests on a cable-stayed bridge with a Pi-shaped girder, and the results indicate that appropriate FMs are effective for suppressing the VIV of the girder under very low structural damping. The FMs have great potential for emergency VIV mitigation because of the low cost, convenience, and rapidity.