結構系統之振動反應能表現系統自身特性，並可反映邊界條件之變化，已廣泛應用於結構系統識別與損傷評估。本文首先利用數值分析，說明橋墩基礎裸露對基礎本身與橋梁上部結構振動反應之影響。另於台三線汶水橋進行現地振動量測，利用頻譜分析與易損指數，實際探討橋墩基礎裸露所造成橋梁上部結構振動特性之變化。並建立汶水橋振動單元模型進行模態分析與動態歷時分析，藉以驗證現地振動量測之結果。由研究成果顯示，量測橋梁上部結構振動反應確有助於評估橋墩基礎之裸露情況。

The vibration of a structure system characterizes the system itself
and also reflects the variation of the boundary conditions. Therefore,
vibration measurement has been widely applied to the system identification and the damage evaluation of structures. In this study,
the influence of pier foundation exposure on the vibrational response of
the foundation itself and the bridge superstructure were first
demonstrated by numerical analysis. Field vibration measurements
were made at the Wensui Bridge of Provincial Highway No. 3 to
actually investigate the variation of vibration characteristics of the
bridge superstructures caused by foundation exposure using the
spectral analysis and the vulnerability index. In addition, the bridge
unit model of the Wensui Bridge was established to perform the modal
analysis and the dynamic time history analysis for the verification of
field measurements. All these results showed that the measurement of
the vibration of the bridge superstructure can be used to estimate the
exposure of the pier foundation.