長跨徑橋梁之受風影響甚劇，而風洞實驗為目前認為可靠的研究方法，但最終仍然需要以實場量測來驗證其準確性。本文以目前國內最長之斜張橋-高屏溪橋為標的，於其主跨二分之一處裝置三維風速計與速度計，主跨三分之一處裝設速度計，以風速計量測颱風經過時週遭之風場特性。同時以速度計量測橋梁速度反應，藉此研究橋梁受風之效應。 本文利用凱米與寶發颱風經過時所紀錄到的資料進行研究，風場特性分析包括分析其平均風向、平均風速、紊流強度、紊流長度尺度及風速頻譜。結構反應則分別使用FDD法與多自由度RD法分析其結構動力特性，包括自然頻率、阻尼比與模態。結果顯示紊流強度隨著風速提高而減小，而順風向紊流長度尺度有隨風速增加有變大的趨勢，風速頻譜則和Karman的經驗公式吻合。由於監測到的平均風速不大，所識別的橋梁振動頻率對於風速變化並不敏感，而橋梁阻尼識別的結果較為散亂。最後將分析得之風場特性與結構動力特性代入數值模式中模擬橋梁抖振抖振反應，並與實場量測及風洞實驗的結果作比較。利用識別的結構參數代入數值模式的結果與實場監測的結果在托曳向的差異較大，約有52%的差異，而垂直與扭轉向則分別有44%與12% 的差異。 The effect of wind excitation on long-span bridges is extremely significant. Such effect is usually studied and analyzed through wind tunnel test which is one of the most reliable methods. However, the predicted results should be verified by field measurements. This study chose the longest cable-stayed bridge in Taiwan - Kao-Ping-Hsi Bridge as the target for field measurements. Two 3D anemometers were installed at the middle point of the longer span to measure the wind characteristics. Two sets of speedometers were respectively installed at the middle point and the one third point of the longer span to measure the dynamic responses of the bridge. Each set of speedometers contain two in vertical direction and one in drag direction. All the speedometers were positioned inside of the box girder.
The measured data including velocity, wind speed and wind direction were continuously recorded during Typhoon Bopha and Typhoon Kaemi attacking Taiwan in 2006. Detailed analysis of these data was conducted in this study. The analysis of wind characteristics includes mean wind direction, mean wind speed, turbulence intensity, turbulence length scale and spectra of wind fluctuations. The dynamic parameters of the targeted bridge, including modal frequencies, damping ratios and mode shapes, were identified by the methods of FDD and RD, respectively. The analyzed results show that the turbulence intensity decreases as the mean wind speed increases. The turbulence length scale in along wind direction increases with the mean wind speed. The measured wind spectrum agrees well with Von Karman spectrum. Since the wind speed is not large enough, the vibration frequencies are not sensitive to the mean wind speed and nearly remain constant. However, the damping rations are varied dispersedly. The identified structural frequencies and damping ratios and the fitted wind spectrum were substituted into the numerical model to evaluate the buffeting responses. The results from the re-analysis, the field measurements and the wind tunnel tests are compared. The comparative study indicates that the differences between the numerical results obtained from the re-analysis and the results analyzed from the field measurements are 12-52%. The discrepancy is larger in drag direction.
