The sensitivity of flutter performance to the angle of attack (AoA) poses a significant challenge for the aeroelastic safety of long-span truss bridges in complex mountainous wind environments. This paper investigates the flutter characteristics and underlying mechanisms of a truss girder through combined free vibration and forced vibration wind tunnel tests. Analysis of system responses identified three AoA-dependent flutter patterns: pure torsional flutter (+7°), torsion-dominated flutter with heaving participation (+3°), and classical coupled flutter (–7°). Self-excited forces and displacements were measured through forced vibration tests, and flutter derivatives were identified. The underlying flutter mechanisms were clarified by analyzing the work done by self-excited forces and the decomposition of aerodynamic damping components. It was found that the accumulation of positive work by the self-excited pitching moment triggers the instability. In contrast, the negative work done by the lift force at –7° enhances stability compared to positive AoAs. Analysis of aerodynamic damping components revealed that negative damping from the uncoupled term component dominates flutter onset. The uncoupled term provides negative damping during flutter, while the contribution of the coupled term to modal damping determines the flutter characteristics. When the positive damping from the coupled term is comparable in magnitude to the negative damping from the uncoupled term, the girder exhibits coupled flutter behavior. These findings provide a theoretical basis for understanding the complex aeroelastic behavior of truss girders under varying attack angles.
Zeng et al. (Fri,) studied this question.