集鹿大橋震害評估與修復之研究

周智傑(Chih-Chieh Chou)

指導教授 ： 張國鎮

國立臺灣大學/工學院/土木工程學研究所/碩士(2004年)

https://doi.org/10.6342/NTU.2004.01127

摘要

1999年9月21日凌晨1點47分，台灣發生了百年難得一見的大地震，這次地震造成全台嚴重的損失，包括人民的生命財產以及房屋、橋梁等結構物的損壞或倒塌。根據中央氣象局地震測報資料顯示，921集集大地震震央位於北緯23.85°、東經120.82°，即日月潭西偏南方12.5公里處，地震規模為芮氏規模7.3，震源深度8.0公里，而在南投縣附近所測得的最大地表加速度更高達1g。
集鹿斜張橋位於南投縣，跨越濁水溪，為通往集集與鹿谷間之一座重要橋梁（即發生地震仍須維持正常通行），由於鄰近集集鎮，為配合觀光需求，是以斜張橋形式建構此橋，盼以結合集集鎮、鹿谷鄉二地，共同發展成一整體性的觀光地區。於921大地震之際，此座由T.Y.LIN顧問公司所設計的斜張橋正值施工的最後階段，除最後四塊因工作車架設需求而尚未安裝的外伸斜撐版及後續的粉飾工作外，全橋大抵完成，卻於此次地震中受到重創。由於目前顯少有斜張橋於地震之中破壞的案例，所以此次集鹿斜張橋於921集集大地震中的破壞頗受各方關注。
本文中，針對集鹿斜張橋的破壞情形先行說明：最嚴重的破壞發生在橋梁的主梁處 (包括了靠近橋塔處及帽梁端)；其餘破壞則是發生在塔體底部 (包括橋塔底部混凝土的剝落及塔底向上延伸13公尺的縱向裂縫)，至於主梁下方P12墩柱底部僅發生微裂縫。關於集鹿斜張橋於地震下之行為本文以SAP2000結構分析程式進行模擬，至於橋梁破壞評估則是藉由比對橋梁於地震中所發生之行為及結構各構件承載力之方式進行。
於階段性修復工作完成之後 (除鋼纜部分外)，為了通行小行車之需要，公路局委託國家地震工程研究中心進行載重試驗，以確保小型車通行的安全性。關於此次試驗，主要包含四部分的測試內容，全橋滿載試驗 (二跨各300公噸重車載)、單跨滿載實驗 (一跨600公噸重車載)、扭力測試 (二跨各300公噸重偏心車載)以及逐步加載試驗 (修復後橋梁性質測試)。有關實驗結果，本文以數值分析進行比對，並探求分析與實驗結果產生差異之原因。
為了配合集鹿斜張橋第二階段鋼纜的修復工程，本文藉由實驗數據配合分析方式找出一組屬於集鹿斜張鋼纜特性的索力計算參數，希望藉由此套參數配合Zui等人所推導出的精算索力公式，能準確的找出鋼纜索力，協助鋼纜的修復工程之進行，使整個修復工作能及早完成。
未來，為了橋梁長期使用安全性的考量，確實瞭解全橋狀態有其必要性。集鹿斜張橋為修復後橋梁，因此橋梁內力的求解上，無法單純以分析方式獲得，所以本文提出一套內力求解的流程，希望藉由頂舉試驗及微振量測的試驗結果先使全橋結構轉換成靜定狀態，然後透過數值分析，初步計算出橋梁內力狀態。

關鍵字

鋼纜索力 ； 載重試驗 ； 集鹿橋 ； 斜張橋 ； 破壞 ； 橋梁內力

並列摘要

A disastrous earthquake struck central Taiwan at 01:47 of September 21, 1999 (Taiwan local time). The Seismology Center of the Central Weather Bureau (CWB) determined the magnitude of this earthquake to be ML 7.3 (CWB) and MW 7.7 (Harvard CMT). The earthquake caused heavy casualties and structural damages to bridges and buildings.
In the damaged areas, the only cable-stayed bridge, called Chi-Lu, was in the final stages of completion at the time of the earthquake. This bridge connected Chi-Chi to the small town of Lu-Ku across the Juoshuei River. Viaducts ran from both banks of the river to the ends of the cable-stayed bridge. The bridge, designed by T.Y. Lin International, was supported on a single pylon, which was connected to the center of the girder by two rows of cables.
In this article, the damages suffered by the Chi-Lu cable-stayed bridge are reported. Severe damage occurred in the deck on the southern side of the bridge. Additional damage occurred in the pylon. Below the girder, the central pier showed evidence of only minor cracking. However, above the girder there were severe spalling of the cover and a crack extended upward nearly to the level of the lowest cables. The seismic performance of the bridge was evaluated by computer modeling. The damages predicted by the computational results were compared to those incurred on the bridge.
Besides, in order to provide limited transportation service for small car after completing first stage retrofit, the Taiwan government asked NCREE to plan a loading test for traffic safety. In this test, there were four parts of design loadings would be considered, torsion, full loading on one span of the bridge, full loading on both spans of bridge and increasing loading gradually. About the results of the loading test, it will be compared with the numerical analysis results, and find the reason for the difference between the two results.
To evaluate the structural safety of the bridge during retrofit phases, the ambient vibration method was applied to measure the time-history vibration data for identifying the dominant frequencies. Then, an empirical method was used to calculate cable forces from measured frequencies. Further, several important parameters used in calculation formula were verified in the arranged tests stage-by-stage in accordance with the retrofit schedule.
In the future, for the safety purpose of the long-term service, it is important to realize the stress status of Chi-Lu cable-stayed bridge. Because of the change of the structural system during retrofit, it is difficult to determine the internal force of the Chi-Lu cable-stayed bridge by only numerical analysis. Therefore, a procedure for determining the internal force of the bridge is brought out in the article. It firstly transfers the structure of the Chi-Lu cable-stayed bridge to be determinate status by using the experimental data of lift-up test and amberiment vibration measurement, and then the stress status of the bridge can be obtained conducting through numerical analysis.

並列關鍵字

Chi-Lu Bridge ； cable stayed bridge ； loadin ； damage

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