橋梁對交通有著重要的貢獻，大部分的橋梁都會橫跨河川。但是每年颱風來臨時，橋梁基礎會因為被大水沖刷而造成樁基礎暴露，進而影響橋梁承載能力，使橋樑崩塌。許多橋樑因為河川沖刷而變成危橋然後損壞。因為橋梁基礎損害常在水面下無法直接觀察判斷，本篇論文利用橋梁監測系統找出橋梁自然頻率來評估樁裸露的程度。首先，不同沖刷深度，不同橋墩高度和土壤強度與不同基樁排列形式的橋樑模型會被建立，接著利用三維連續元素(稱為有限元素分析)及彈簧元素(稱為簡單元素分析)來解決土壤-橋梁互制問題進而找出橋梁的自然頻率，然後可以得到橋梁的自然頻率及基礎沖刷深度得相互關係來預測樁基礎的暴露深度。最後，比較簡單元素分析及有限元素分析結果，結果指出用簡單元素與有限元素分析結果相似。

Bridges have an important contribution to traffic, and most of bridges are across the river. However, typhoons every year could scour the foundation of bridges, and the bridge damages caused by foundation exposing in the rivers may create shortage of the foundation carrying capacity that bring bridge to collapse. There are many of dangerous bridges in Taiwan because of scour in rivers. Since the bridge foundation damage always underwater and cannot be observed directly, the bridge-monitor-system is made to find the bridge natural frequency and estimate the pile exposure level in this thesis. In the beginning, the bridge models for the several foundation scour depth with the different pier length, soil strengths and the different style of the pile foundations are created, then use three-dimensional continuous elements (called finite element analysis) and spring elements (called simple element analysis) to solve the soil-bridge problem and determine the bridge natural frequency . Afterward, the bridge natural frequency and the foundation scour depth interaction can be obtained to predict the exposure of pile foundation. Finally, comparing the simple element analysis and finite element analysis results indicates that the two methods obtain similar results.

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