悬索桥静风扭转发散的影响因素研究

基于索-梁体系广义模型揭示了主缆系统刚度退化是导致大跨度悬索桥静风扭转发散的主要原因.研究了主缆和桥塔的变形对悬索桥刚度退化的影响.理论分析表明,主缆的竖向运动对系统的扭转刚度影响至关重要,当任何一条主缆向上的竖向位移足够大时,主缆将处于松弛状态,进而导致系统的扭转刚度急剧下降.因此,主缆竖向运动引起的刚度退化是大跨度悬索桥发生静风扭转发散的关键原因.本文的研究还表明主缆的侧向位移和两座桥塔塔顶之间沿桥轴方向的相对变位对主缆的刚度退化起延缓作用,从而提高临界竖向位移.此外,紊流对扭转发散的影响不容忽视,紊流明显降低了桥梁结构的静风扭转稳定性.本文的理论成果可以尝试性地解释西堠门大桥非线性有限元分析的数值结果.

Research of Influencing Factors on Aerostatic Torsional Divergence of Suspension Bridges

Based on a generalized cable-girder model, it was found that the torsional stiffness degradation of the cable system was the essential reason leading to aerostatic torsional divergence of long-span suspension bridges. The effects of the deformations of the main cables and the bridge tower on the stiffness degradation of suspension bridges were investigated. Theoretical analysis indicates that vertical deformation of the main cable is critical to the torsional stiffness of the whole system. Provided that the vertical deformation of any cable reaches a critical value, the cable will loosen up to a non-stress state, which causes a sudden drop in torsional stiffness of the system. Therefore, it is stated that the sudden drop in stiffness due to the vertical deformation could be the key reason for the aerostatic torsional divergence of a long-span suspension bridge. Moreover, the study also shows that lateral deformation of the main cable and the horizontal relative deformation between the two tower-tops postpone the stiffness degradation, and hence enhance the critical vertical deflection. In addition, it is shown that the effect of turbulence on torsional divergence is non-negligible, and the turbulence significantly decreases the aerostatic torsional stability of bridge structures. Numerical results of the Xihoumen Suspension bridge performed by nonlinear finite element simulation could be explained tentatively by the theoretical viewpoints proposed in this paper.