Full bridge aeroelastic testing and three-dimensional nonlinear flutter behavior of a 2180 m truss suspension bridge

The development of super-long-span suspension bridges has entered a critical stage in which aerodynamic stability is increasingly governed by low structural stiffness, low damping and complex aeroelastic coupling. This study presents a full bridge aeroelastic model test of a double-deck truss suspension bridge with a main span of 2180 m. A modeling method combining carbon fiber truss-girder segment fabrication with distributed stiffness simulation using U-shaped springs is proposed to reproduce the multimodal and damping characteristics of the prototype bridge while preserving the aerodynamic shape of the truss girder. Wind tunnel tests were conducted to investigate three-dimensional (3D) nonlinear flutter under different angles of attack (AoAs) and yaw angles. The results show that torsional flutter dominates the bridge responses at all tested AoAs: hard flutter occurs at 0°, self-limiting soft flutter occurs at ±3°, and pronounced hysteresis with a subcritical Hopf bifurcation appears at −3°. Yawed inflow increases the critical flutter wind speed, broadens the range of bounded oscillations before divergence, and produces beating responses, while the final instability remains divergent. A generalized displacement-based method for three degrees of freedom (3DOF) coupled trajectory characterization, full modal decomposition and reconstruction is further proposed. The results characterize the 3D multimodal response and identify the principal modal response components of the main girder, providing experimental evidence and theoretical support for nonlinear flutter analysis and the wind resistant design of ultra-long-span suspension bridges.