由於台灣之特殊地理位置與地形，使得島內橋梁於雨季中經常飽受洪水衝擊與面臨崩塌之危機。其中，人為與天然的災害造成河道改變、河床沖刷、以及基礎淘空，大幅地提升橋梁倒塌的機率，如何避免或減輕橋梁倒塌所造成的損失成為一項重要的課題。本論文研究預力混凝土橋梁的倒塌行為，首先以雙園大橋於莫拉克颱風時的結構設計與河床環境為範例，探討極端洪水作用與河床沖刷對橋梁行為之影響，並使用替代路徑法分析預力混凝土橋梁的逐漸倒塌機制，最後提出有效的補強方案，避免預力混凝土橋梁產生全面式的逐漸倒塌。Frequent strong typhoons in Taiwan often cause flooding that consequently results in the scouring of bridges crossing rivers. The exposure of pier foundations due to scouring reduces the foundation bearing capacity to resist floods and earthquakes. The objective of this dissertation is to evaluate the influence of scouring and exposure of piles on the behavior of bridges under floods. A complex and detailed three-dimensional finite element model is developed to study the nonlinear behavior of prestressed concrete bridge. Valuable insights into the influence of exposure of piles on the bridge behavior subjected to flooding are obtained. In addition, the mechanism of progressive collapse for scoured bridges is identified using the alternative path method. Appropriate retrofit strategies are suggested accordingly.
