Geometrically nonlinear effects on coupled vertical-torsional soft flutter of a flat closed-box bridge deck section

As bridge spans continue to increase, bridge deck sections are more susceptible to soft flutter with large-amplitude vibration under wind action. However, most existing wind tunnel studies and computational fluid dynamics (CFD) simulations employ geometrically linear structural models, making it difficult to accurately capture the dynamic characteristics of soft flutter at large amplitudes. In this study, by taking a flat closed-box bridge deck section installed on a spring-damper suspension system in a wind tunnel as a background, a geometrically nonlinear structural model of coupled vertical-torsional soft flutter and its equations of motion are established. CFD solutions for large-amplitude coupled vertical-torsional soft flutter, considering a fluid solver and a structural solver with fluid–structure interaction, are figured out. After the CFD solution for small-amplitude soft flutter is validated against wind tunnel test results, the large-amplitude soft flutter responses of the deck section under high wind speed conditions are investigated. The evolutions of aerodynamic input energy, structural mechanical energy, and damping dissipation are analyzed. The effects of mechanical parameters on large-amplitude soft flutter are also investigated. The results show that the proposed geometrically nonlinear model can produce major vibration features of large-amplitude soft flutter, which are significantly different from the traditional geometrically linear model.