| Summary: | 博士 === 國立中央大學 === 土木工程研究所 === 100 === 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.
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