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

本文研究斜拉桥拉索的气动振动抑制问题。斜拉桥的多索系统由于迎风拉索的尾迹而固有地引起尾迹驰振。虽然已经进行了大量的研究来抑制尾迹驰骋，但还没有找到一个好的解决方案。在本研究中，在弄清尾流舞动机理的基础上，提出了一种新的缆索系统。它被命名为一种紧密而刚性连接的电缆。根据本研究阐明的机理，当缆索间距小于3.56D(D为缆索直径)时，发生硬尾流舞动，当缆索间距大于3.56D时，发生软尾迹舞动。3.56D的数值与卡门涡街理论有很强的相关性。由于尾流驰振是由于下风索存在于迎风索尾迹影响背风索的区域而引起的，因此，为了消除迎风索尾迹的影响，可以将迎风索靠近迎风索来抑制尾迹驰振。即使背风缆索以1.3d的间隔放置，尾迹舞动的幅度也相对较小。为此，提出将两根拉索刚性连接起来，用静止的迎风拉索来约束下风拉索的振动运动。实验结果表明，为了减小紧连缆索的气动幅值，两根缆索之间的最佳间距为I.25D。为了了解振动机理，测量了静止和振动状态下气动力和表面压力的三分量。该索系被应用于日本跨度最长的PC斜拉桥--伊卡拉大桥。

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.