Aerodynamic Stability of Long-Span Bridges in Post Flutter

To provide reasonable explanations for the motion types of girder in post flutter status of long-span bridges, the nonlinear aerodynamic stability of bridge girder was analyzed based on an existing nonlinear motion-induced aerodynamic force (MIAF) model and the nonlinear vibration differential equation, by using the 4th Runge-Kutta algorithm. Four typical MIAF cases of streamline box girder with large vibration amplitudes were taken into account in the analysis. The results show that different types of motions would occur to the girder of long-span bridge in post flutter under conditions of different amplitudes and reduced velocities. The vibration of bridge girder will converge when the aerodynamic work is negative only or the negative work is larger than the positive one. The divergent motion will occur when the aerodynamic work is positive only or the positive work is larger than the negative one. If the aerodynamic positive and negative work are well matched to each other, the girder vibration will converge slowly because of the structural damping. If the aerodynamic positive energy is equal to that consumed by structure in the same period, an equal-amplitude vibration will occur. The motion of bridge girder could diverge if ignoring the nonlinear items of the motion-induced aerodynamic force.