Spanwise-differentiated flutter suppression in long-span suspension bridges using an extended modality-driven approach

An extended modality-driven approach is proposed to enable cost-effective three-dimensional flutter control in long-span suspension bridges. This method quantitatively characterizes aerodynamic contributions along both the spanwise direction and the entire bridge, emphasizing their spatial variations and establishing a theoretical foundation for spanwise-differentiated control strategies. A case study of a closed-box girder suspension bridge demonstrates that flutter is governed by complex multimode coupling, involving the first-order torsional, first-order vertical, and second-order vertical vibration modes. The interaction of these modes produces a distinct three-dimensional aerodynamic contribution profile with an hourglass-shaped distribution. Along the span, positive contributions dominate near the mid-span, negative contributions appear around the quarter-span regions, and edge spans have minimal influence. Across the cross-section, a decreasing gradient is observed from the windward to the leeward side, with the windward lower surface exhibiting strong aerodynamic effects. Based on this distribution pattern, the central 50% of the span is identified as the critical control zone. Parametric studies on spanwise slotting ratios confirm that targeted aerodynamic control in this region provides protection comparable to full-span interventions. These findings not only validate the feasibility of the proposed approach for spanwise-differentiated flutter control but also contribute to the advancement of more refined flutter suppression techniques.