| Summary: | 碩士 === 淡江大學 === 土木工程學系碩士班 === 104 === Some cable-supported bridges have been designed or built in mountainous areas in Taiwan. Due to the complex terrain, not only the variations of wind speed but also the possibility of large angle of wind attack should be considered in the investigations of the aerodynamic responses of the cable-supported bridge built in these areas. The angle of wind attack for the bridge built in the complex terrain has been found in the literature as large as fifteen degrees or more. At the large angle of wind attack, the difficulties have risen in full bridge model tests. Therefore, the measurement of the section model responses is the only way to investigate the aerodynamic behavior of the bridges built in the complex terrain. Effects of large angles of wind attack on the flutter wind speeds and buffeting responses of bridges are investigated in this thesis. A typical pedestrian suspension bridge is chosen as the example for the investigation.
The experimental results show that the flutter wind speeds decrease with the increases of angles of wind attack. The trend is more obvious as the angle of wind attack is larger than 6.5 degrees. The flutter wind speed may decrease 40% as the angle increases from 6.5 degrees to 8.5 degrees. As we expected, the increases of turbulence intensities will increase the flutter wind speeds for all angles of wind attack. The increase of the torsional -vertical frequency ratio of the section model will increase the flutter wind speed significantly. The results also show that the increase of angles of wind attack increase the responses buffeting in all directions. At the wind speed of 30m/s, the vertical response at the angle of 10 degrees increase 84% compared to that at the angle of zero degree. The large amount increases are also found in drag and torsional directions.
Since the large angles of wind attack may occur for the bridges built in the complex terrain, the aerodynamic behavior of these bridges should be carefully examined.
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