| Summary: | 碩士 === 國立中興大學 === 土木工程學系所 === 99 === In this study, I investigated the eccentricity effect on the aerodynamic instability of a suspension bridge in the uniform flow field. The experiments were conducted in Wind Tunnel Laboratory of the Agricultural Experimental Station of the National Chung Hsing University. I used a simple rectangular cross-section model as a bridge’s basic body shape. The effects on the dynamic reaction of the bridge plate were investigated based on a two-dimensional approach. Measurements of the dynamic reaction of the bridge plate were implemented by changing the flow speed, frequency ratio of the first mode (heaving direction) and the second mode (torsional direction), eccentric mass site (0%, ±5%, ±10%) and angle of attack (0°, 4°, 8°).
On the premise, the first mode (heaving direction) frequency was constant. At different frequency ratios, the eccentric mass will cause interaction effects on the bridge. The interaction effects were investigated by analyzing the root-mean-square values of the vertical displacement of the bridge’s body and the changes of the angles in the torsional direction.
According to the experimental results, I found that, under the same eccentricity conditions, the aerodynamic stability improved while the frequency ratios increased. The flutter critical velocity increased along with the frequency ratios. Under the same frequencies, when the angle of attack was 0°, the aerodynamic stability was the best when the eccentric mass site was downstream, and then non-eccentric, with the worst when upstream; when the angle of attack was 8°, frequency ratio at 1.2 and 1.35 except when the eccentric value was ±5%, the aerodynamic stability was the best when the eccentric mass site was downstream, and then non-eccentric, with the worst when upstream
The dynamic reactions from the conditions while the frequency ratio was 1.2, the upstream eccentricity was -10% and the angles of attack were 0°, 4°, 8°, and that while the downstream eccentricity was +10% and the angle of attack was 0° were different from those of the other frequency ratios.
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