Multimodal Control of Vortex-Induced Vibration of a Long-Span Suspension Bridge Using MR Dampers

Due to their high flexibility and low damping, long-span suspension bridges are susceptible to multimodal vortex-induced vibration (MVIV) under low and normal wind speeds. However, it remains a challenge for the currently used control strategies to achieve optimal additional damping ratios for different modes of vibration as wind speed varies. To this end, this study presents a multimodal control strategy for mitigating MVIV of long-span suspension bridges using magnetorheological (MR) dampers. A vortex-induced force (VIF) model is first established based on the VIFs identified from the wind and structural responses of a bridge during MVIV measured on site. The MVIV of the bridge is then simulated by applying the VIF model to the finite element model of the bridge, and the optimized setup of the control system, consisting of MR dampers and supporting brackets, is sought in terms of a passive control strategy. The multimodal control strategy, which is a novel semiactive control strategy, is finally proposed based on the self-excited characteristics of MVIV observed on site and a linear quadratic regulator. To demonstrate the effectiveness and robustness of the proposed control strategy, a real long-span suspension bridge once suffering MVIV is chosen as a case study. The results demonstrate that the proposed control strategy can robustly mitigate the MVIV of the bridge in the first fourteen modes of vibration in vertical direction, and the effectiveness of the proposed strategy is superior to passive or other semiactive control strategies.