本研究於台灣某橋設計並建置橋梁健康監測系統，記錄橋梁使用外置預力補強過程的短期與完工後的長期行為，監測項目包含溫度計、應變計與傾斜計，監測項目包含大氣溫度、箱梁溫度、橋體溫度、箱梁應變與縱向、橫向轉角，其中傾斜計的縱向轉角進一步以二次撓曲線近似法計算出橋體位移。兩年半的監測資料中，包含了外置預力補強過程的橋體應變及完工後的長期位移與應變。因大跨度箱型梁橋的變形受到溫度的影響相當顯著，容易影響資料的判讀，本研究中以全相經驗模態分解法（ensemble empirical mode decomposition, EEMD）作為資料分析的主要方法，將監測資料拆解成為數個本質函數，並進一步應用其中的日週期與年週期的分量進行分析。在本案例中，橋梁長期位移主要受到環境溫度與外置預力損失的影響，研究中以年週期的溫度與位移關係進行回歸，得到兩者間的關係後，用於消除位移資料中的長期溫度影響，使資料更容易研判預力損失的影響；日週期應變資料則應用於計算橋梁斷面中性軸位置，中性軸位置為斷面勁度的重要參數，因此可以作為橋梁的狀況指標。A 889 days performance evaluation of a prestressed concrete box girder viaduct retrofitted by external postensioning tendons is presented in this thesis. A PC viaduct exhibits substantial vertical deflection ever since construction completion. External postensioning tendons were designed and installed to increase the load carrying capacity and to lessen the deflection of the bridge. Deflection curves are calculated based on an approximation model using the tilting angles measured at five points along the girder. In this case, the deflection of bridge varies due to two chief parameters, prestress loss and temperature changes, in the long-term monitoring data. To extract the prestress-loss part in overall deflection data, the Ensemble Empirical Mode Decomposition (EEMD) method is used. Finite intrinsic mode functions (IMFs) without mode mixing were then obtained by EEMD method. Daily and annual components were identified from IMFs and applied in calculating the variation of neutral axis position of cross-section with time and eliminating thermal effects from deflection data. The data analysis process and monitoring program is introduced in this thesis.
