在河床上新建單柱式橋梁,經過一次又一次的洪水沖刷後,橋梁的基礎可能已經裸露,橋梁耐震能力會因為裸露之後變差,而需要進行增樁補強。橋梁耐震設計規範規定當地震發生時,橋梁基礎必須要保持彈性,但使用此方法進行計算補強增樁所用的量較大,對於單柱式橋梁設計而言並非相當經濟。因此本研究將以兩種補強方法、三種已經裸露深度設計橋梁,第一種方法是以柱底產生塑鉸對應之彎矩、剪力傳入基礎進行增樁設計,並且依循規範將增樁加以圍束;第二種方法則以載重組合對於橋梁下部結構進行增樁,允許樁頂產生塑鉸,並且依循規範將增樁加以圍束;三種已經裸露深度分別為三公尺、六公尺、九公尺。爾後將以上二種方法所設計之橋梁利用容量震譜法進行耐震能力評估,最後再進行災損分析,求得新建並補強增樁橋梁在一年內之總支出再加以比較。 本研究將以容量震譜法求得不同沖刷深度下之耐震能力,並將地震損壞分為無損壞、輕微損壞、中度損壞、嚴重損壞與完全損壞,再配合橋梁耐震能力的變異係數,求出各地表加速度下,發生各級破壞的或然率。並以不同地表加速度對應之年超越機率曲線模擬橋址之地震危害度曲線。而各級損壞的修復費用,將以佔結構新建成本的比例,即損失比來計算。然而考慮橋梁於一年內的裸露深度為一隨機變數,因此將建立一完全回淤或然率曲線進行災損分析,最終比較二種方法之經濟性。
A new single column bridge is built in the riverbed that is scoured in course of again and again floods, the pile of base can be uncovered, therefore, aseismatic capability of the bridge can be worse and then it needs to retrofit new piers. The Seismic Design Specifications for Highway Bridges provide that pier of the bridge must maintain the elasticity when the earthquake comes up. But this method is not very economical for single column bridge. Therefore, the study will retrofit new piers with two method. The first kind is by static analysis as the Seismic Design Specifications to retrofit new piers and increases the stirrup. The second kind is by load combination to retrofit new piers of bridge substructure. And increases the stirrup to allow that plastic hinge occur at top of pile. The three uncovered depths already is 3 meters, 6 meters, and 9 meters. Then use the Capacity Spectrum Analysis (CSA) to determine their aseismatic capability and damage analysis. And makes the comparison of two methods. This study uses the CSA to determine the seismic capability at different depth of base plane then to divided the earthquake damage into no damage, slight damage, moderate damage, extensive damage, and complete damage. Moreover, this study also uses the Coefficient of Variation (CV) of the seismic capability to calculate the incidence of each damage levels on Peak Ground Acceleration (PGA). And using the annual excess probability curve correspond the different PGA to simulate the seismic hazard curve based on the location of the bridge. The repair expenses of all levels will be calculated with the percentage of the cost of the new bridge. Finally, it establishes one probability curve in the exposed depth of the location of the bridge to proceed the damage analysis. It considers that the exposed depth in a year as a random variable, Finally compares efficiencies of the two method.
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