| 摘要: | 長跨徑人行拱橋近年來深受工程師青睞，此型橋梁除滿足交通需求外，更能扮演當地景觀地標角色。因人行橋面版窄大多採用單拱設計，由於單拱缺乏側向支撐，拱順風向之氣動力反應也越趨明顯。而傳統斜張橋或懸索橋氣動力分析只考慮橋面版風力，因此無法適用於拱橋上。所以本研究建立一數值分析模式，以主梁斷面及橋拱斷面之顫振導數及風力係數為基礎，推導整體橋梁顫振與抖振理論。並採用兩例題，分別為單面吊索及雙面吊索拱橋，利用所推導之數值分析模式，配合橋拱斷面實驗求得之實驗數據進行顫振與抖振分析，來探討加入橋拱氣動力參數對整體顫振臨界風速與抖振位移反應影響。
例題結果顯示，橋梁顫振臨界風速主要受主梁氣動力控制，所以將橋拱順風向顫振導數（P1*、P4*）納入分析時，其對顫振影響並不顯著，兩例題之臨界風速提高不到1%。至於抖振分析，兩例題結果都顯示拱風力對拱及主梁順風向及扭轉向反應有顯著影響。當橋面高度之平均風速60m/s時，加入橋拱風力對例題一主梁順風向與扭轉向之抖振位移反應分別提高1.9%及44.11%；至於對橋拱本身順風向及扭轉向分別提高了764%及792%。由於此例題橋拱與主梁結構耦合不明顯，拱反應主要是作用於拱的風力貢獻，因此才有上述巨幅提升。例題二方面，風速60m/s時加入橋拱風力對橋面版順風向與扭轉向則分別提升了11.99%及133%；橋拱順風向及扭轉分別向則分別提高了57.87%及64.6%。此例題橋拱與主梁結構耦合較例題一明顯，作用於拱的風力對主梁及拱本身抖振反應都有明顯貢獻。由上述分析結果顯示，無論是單面吊索或雙面吊索橋，拱風力對主梁及拱本身抖振反應影響極為顯著，因此分析時須詳加考慮。
The long-span arch bridges have been a favorable choice for the design of pedestrian bridges during the past decades in Taiwan. This is because the type of bridges not only can satisfy the transportation needs but also may become the landmark in the local area. In these pedestrian bridges, a single arch is the only choice due to the narrow bridge deck. Since the single arch lacks lateral support and its height increases with the bridge span length, the drag responses in the arch become significant and cannot be negligible. To predict the aerodynamic responses of the arch, the traditional analysis used for cable-stayed and suspension bridges, considering wind forces acting on bridge decks only, cannot be used. In this thesis, an analytical approach based on flutter and buffeting theory associated with the information measured from section model tests is presented. Two examples are used to demonstrate the validity and applicability of this approach and to investigate the effects of the forces acting on the arch on the flutter wind speed and buffeting responses of bridge decks.
The results show that the critical flutter wind speeds in these two examples are dominated by the flutter derivatives of bridge decks. The increases of the critical flutter wind speeds considering flutter derivatives of arches are less than 1%. For the buffeting responses, the effects of the forces acting on arches are significant on both drag and torsional responses of arches and bridge decks. In Example 1 incorporating forces acting on the arch into the analysis, the drag and torsional responses of the bridge deck increase 1.9% and 44.1%, respectively. The increases of the drag and torsional responses of the arch are 764% and 792%, respectively. Since the structural coupling between the bridge deck and the arch is minor in this example, the main contribution to the responses of the arch is the forces acting on the arch itself. Therefore, the results with huge increases are expected. In Example 2 incorporating forces acting on the arch into the analysis, the drag and torsional responses of the bridge deck increase 11.99% and 133%, respectively. The increases of the drag and torsional responses of the arch are 57.87% and 64.6%, respectively. In this example, the structural coupling between the bridge deck and the arch is more obvious than in example 1. The effects of the forces acting on the arch on the responses of the arch and the bridge deck are significant. From the results stated above, the forces acting on the arch should be considered in the analysis. |
