一般而言，橋梁氣動力效應以顫振及抖振最為顯著，也最受到關注。傳統上對於顫振及抖振分析，因實驗技術不易絕大多數僅考量垂直向與扭轉向顫振導數，忽略順風向顫振導數作用之影響。但隨著長跨徑橋梁的出現，忽略順風向顫振導數影響的思維，對於實際存在的氣動力行為可能已經不再保守。此類長跨徑橋梁通常採用輕質材料及纜索支撐系統，側向運動將會比短跨徑橋梁更為顯著，也可能產生順風向與扭轉向之耦合振態。 本文採用斜張橋、懸索橋、吊索拱橋三類纜索支撐橋梁例題，配合文獻中之顫振導數進行顫振與抖振分析。此外，在多振態分析中，針對不同振態組合、耦合振態的參與，以及順風向振態、順風向顫振導數的參與等情況下，探討各情況對例題橋梁之臨界顫振風速及抖振位移反應的影響。分析結果顯示，順風向與扭轉向耦合振態以及順風向顫振導數對橋梁氣動力的影響隨跨徑增長而增加，因此分析時須予以考慮。此外，本文所採用之兩類橋面板斷面，其順風向顫振導數 具有提高氣動力穩定性之效果，而 則具有降低氣動力穩定性之效果。 In general, the most important effects of bridge aerodynamics are flutter and buffeting. In the past, owing to the experimental technique, we always ignore the effects of lateral flutter derivatives, and only consider vertical and torsional flutter derivatives in the flutter and buffeting analysis. However, ignoring the lateral flutter derivatives may not reflect the real aerodynamic behavior of long-span bridges. Such bridges are usually made of lightweight materials and supported by cable systems. The lateral motions on this type of bridges are significant and usually coupled with torsional motions.
Three types of bridges, including cable-stayed bridges, suspension bridges and tied arch bridges, are used in the examples. The lateral flutter derivatives, adopted from references, are used in the multi-mode flutter and buffeting analysis. The effects of mode combinations and the lateral flutter derivatives on the flutter wind velocities and buffeting responses of different types of bridges are investigated through a parametric analysis. The results show that the contributions of the lateral-torsional coupling modes and the lateral flutter derivatives on the aerodynamic behavior of bridges increase with bridge span lengths. These effects should be taken account into the aerodynamic analysis for the long-span bridges. The results also reveal that of the flutter derivatives used here can stabilize the aerodynamic effects and can destabilize the aerodynamic effects.
