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<p> Since the longest stay cables of the Tatara Bridge are about 460 m, various wind tunnel tests were carried out. As a result of the tests, it was found that an indent cable is very effective against rain vibration and the indent cables were applied to the bridge for the first time in the world. It was also found that smooth wind flow without rain is possible to generate large amplitude vibration. As it was thought that this vibration was rarely generated due to actual wind condition, it was decided that countermeasures against this vibration were studied based on monitoring results, if necessary. Monitoring of the cables has been conducted with measurement of wind and rain fall. Although medium amplitude vibration, which was not rain vibration, was observed on the short indent stay cables, harmful vibration such as rain vibration has not been observed until now. Therefore, it was confirmed that the indent cable is effective against rain vibration.</p>

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<p>The Shimotsui-Seto Bridge, Kita Bisan-Seto Bridge and Minami Bisan-Seto Bridge are highway- railway combined suspension bridges in the Seto-Ohashi Bridges, which connect Honshu Island and Shikoku Island in Japan. Cross sections of stiffening truss girders of the bridges are identical and have two levels for transportation. Upper level and lower level are for highway and railway, respectively. In order to satisfy the aerodynamic stability, open gratings are installed at the center divider and both sides of road deck. However, since small objects may drop through them and endanger railway operation, it is disadvantageous to use them in terms of maintenance.</p><p>In order to minimize range that requires open gratings, aerodynamic stability of the bridges was re-evaluated by three-dimensional flutter analysis. This analysis method was developed after the completion of the Seto-Ohashi Bridges. From the analysis, it was found to be possible to minimize the range that requires center gratings. Also, it was found to be possible to close all center gratings by installing center barrier.</p>