大跨度桥梁颤振后状态气动稳定性

Aerodynamic Stability of Long-Span Bridges in Post Flutter

为了能对大跨度桥梁颤振后主梁的运动形式给出合理解释,选取大振幅下流线型箱梁断面的4种典型非线性气动力工况,基于非线性气动力和非线性振动微分方程,应用四阶龙格-库塔算法,分析了大跨度桥梁主梁在大振幅条件下的气动稳定性.结果表明:大跨度桥梁主梁在颤振后的不同振幅和折算风速条件下可出现不同的运动形式;若气动力仅做负功或负功显著大于正功,主梁振动将收敛;若气动力仅做正功或正功显著大于负功,主梁振动将发散;若气动力做的正负功相当,主梁振动将由于结构阻尼缓慢收敛;若气动力正功与相同周期内结构消耗的能量相等,主梁将发生等幅振动;若不考虑气动力的非线性项,桥梁振动可能发散.

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.