曲線斜張橋之顫振與抖振研究

Flutter and Buffeting Analysis of Curved Cable-Stayed Bridges

黃明慧(Ming-Hui Huang)

指導教授 ： 林堉溢

淡江大學/工學院/土木工程學系博士班/博士(2012年)

https://doi.org/10.6846/TKU.2012.01354

摘要

隨著橋樑工程的快速發展，近代的懸索支撐橋樑除了基本的交通功能外， 外型上的設計也越來越多元，曲線造型的設計亦是相當常見的設計。當曲線橋 體結構受風作用時，其風向角是沿著橋軸而變化，若以有限元素的觀點來看， 亦即表示每一節塊桿件與來流之間的風向角均不相同，正因如此，一般會將其 視為橋樑受斜風作用的衍生。在過去經常使用餘弦法則(Cosine Rule)以及斜風理 論(Skew Wind Theory)等近似方法來模擬此些不同風向角下的節塊斷面之風效 應，但是，這些近似理論僅能適用於小風向角或是低風速的情況下。 本文旨在針對曲線結構發展一套完整且較為嚴謹的顫振理論與抖振理論。 曲線理論中直接以斷面風洞實驗方式考慮不同風向角下之氣動力參數，而不以 近似方法進行模擬。文中亦設計一座曲率半徑及夾角分別為250m 及60°的曲線 斜張橋樑，其斷面則採用寬深比為5 之矩形斷面，並以縮尺全模型風洞實驗的 方式來驗證比較本文所提出曲線理論。 實驗結果顯示，在無初始風攻角以及風向角的情況下，曲線斜張橋樑的顫 振臨界風速約為85.38 m/s，本文所提出之曲線理論與餘弦近似方法的預估差距 均在1%以內。就抖振反應而言，餘弦近似法在高風速下高估了橋體垂直向擾動 均方根值；曲線理論與餘弦近似法對於拖曳向擾動均方根值均有良好的預估結 果；兩方法均高估了高風速下的扭轉向擾動均方根值，特別是餘弦近似法，此 高估現象極有可能是因為紊流削減了氣動力阻尼A2 *對結構扭轉阻尼的影響

關鍵字

曲線斜張橋 ； 風向角 ； 顫振 ； 抖振 ； 全模型風洞實驗

並列摘要

Attributed to the developments of bridge engineering, modern cable-supported bridge
design requires not only the needs of transportation but also the aesthetical appearance. As
the curved bridge is subjected to wind excitation, the yaw angles along the bridge axis are
continuously varied because of the curved appearance. In other words, the yaw angle of each
deck element is different in the finite element analysis. Therefore, the wind effects on the
curved bridges can be regarded as the further applications of straight bridges under various
yaw winds. In conventional analysis, the “Cosine Rule” and the “Skew Wind Theory” were
often used for dealing with these effects. However, these approximate theories were
demonstrated valid only for small yaw angles or low wind speeds.
This study aims at developing a reasonable theory for flutter and buffeting analysis of
the curved bridge. The proposed method is based on the aerodynamic coefficients and the
flutter derivatives obtained from section model tests for different yaw angles. In order to
demonstrate the validity and applicability of the theory, a curved cable-stayed bridge was
designed and the full aeroelastic model test was conducted. A rectangular cross section with
the width-to-depth ratio of 5 was adopted for the bridge. The curvature and the included angle
of the target are 250 m and 60°, respectively.
The experimental results show that the critical flutter wind speed is about 85.38 m/s. The
numerical predictions obtained from both the proposed theory and the Cosine Rule are less
than 1%. For the buffeting responses, the Cosine Rule overestimates the vertical responses
especially at high wind velocities. The results obtained from both the proposed theory and the
Cosine Rule agree well with the experimental results in the drag direction. However, both the
proposed method and the Cosine Rule overestimate the torsional responses. The phenomenon
is more obvious for the results predicted from the approximate method. The possible reason
for the discrepancies in the torsional responses is that the negative aerodynamic damping is
overestimated in the section model test under smooth flow.

並列關鍵字

curved cable-stayed bridge ； yaw angle ； flutter ； buffeting ； full aeroelastic model

參考文獻

1. Kubo, Y., Miyazaki, M. and Kato, K., “Effects of end plates and blockage of structural members on drag forces”, Journal of Wind Engineerring and Industrial Aerodynamics, Vol 32(3), pp. 329-342 (1989)

4. Vickery, B. J., “Fluctuating lift and drag on a long cylinder of square cross-section in a smooth and in a turbulence stream,” Journal of Fluid Mesh.25, pp. 481-494 (1966).

5. Saito, T., Shiraishi, N. and Ishizaki, H., “On aerodynamic stability of double-decked / trussed girder for cable-stayed “Higashi-Kobe Bridge” ,”Journal of Wind Engineering and Industrial Aerodynamics, Vol 33(1-2), pp. 323-332 (1990).

6. Santo, H. P., Branco, F. B., “Wind forces on bridges–numerical vs. experimental methods,” Journal of Wind Eng. and Industrial Aerodynamics, Vol 32(1-2), pp. 145-159 (1989).

9. Hikami, Y. and Shiraishi, N., “Rain-wind induced vibrations of cable Stayed bridges,”Journal of Wind Engineering and Industrial Aerodynamics, Vol. 29(1-3), pp.409-418 (1988).