STUDY ON SUPPRESSION OF AERODYNAMIC VIBRATIONS OF BUNDLE CABLES FOR SUPER LONG CABLE-STAYED BRIDGE

针对斜拉桥多索体系中迎风索尾流诱发驰振的问题，研究了斜拉桥拉索气动振动的抑制方法。针对尾流舞动的抑制问题，国内外学者进行了大量的研究，但至今没有找到一个很好的解决方案，本文在明确尾流舞动机理的基础上，提出了一种新的拉索系统。它被命名为紧密刚性连接的电缆。研究表明，当两条拉索的间距小于3.56D（D为拉索直径）时，发生硬型尾流驰振，当间距大于3.56D时，发生软型尾流驰振。3.56D的值与卡门的涡街理论密切相关。由于尾流驰振是由于背风拉索存在于迎风拉索的尾流影响背风拉索的区域中而引起的，因此认为可以通过将背风拉索靠近迎风拉索放置来抑制尾流驰振，以消除迎风拉索的尾流影响。即使背风拉索间距为1.3D，尾流驰振的幅值也相对较小。因此，提出了将两条拉索刚性连接，通过静止的迎风拉索来约束背风拉索的振动运动。实验结果表明，两条索之间的最佳间距为1.25D，以减小紧密连接的索的气动振幅。为了了解振动机理，在静止和振动状态下测量了三分量气动力和表面压力。所提出的缆索系统被用于日本最长跨度的PC斜拉桥--伊卡拉桥。

The present research deals with suppression of aerodynamic vibrations of cables for a cable-stayd bridge.A multi-cable system for cable-stayd bridge inherently induces wake galloping due to wake of a windward cable. Although a lot of studies have been conducted to suppress the wake galloping, a good solution have not yet been found. In the present study, after making clear the mechanism of wake galloping, the new cable system was proposed. It was named as a closely and rigid connected cable. According to the mechanism made clear in the present study, when the interval both cables less than 3.56D (D is a diameter of cable), a hard type wake galloping occurs and when the interval is larger than 3.56D,a soft type wake galloping occurs. The value of 3.56D is strongly related with Karman's vortex street theory. Since the wake galloping was induced by the reason that the leeward cable existed in a region where the wake of the windward cable affected leeward cable, it was considered that it was possible to suppress the wake galloping by putting the leeward cable closely to the wind ward cable in order to get rid of influence of wake of the windward cable. Even if the leeward cable was put with interval of 1.3D,the wake galloping occurred in relatively small amplitude. Therefore, it was proposed to rigidly connect both cables to restrict the vibrating motion of leeward cable by the motionless windward cable. As a result of the experiments, it was made clear that the optimum interval between both cables was I.25D to reduce the aerodynamic amplitude of the closely connected cables. In order to understand the vibration mechanism, 3-component of aerodynamic forces and surface pressure at rest and vibrating states were measured. The proposed cable system was used for the lkara bridge that is the PC cable-stayd bridge with the longest span length in Japan.