由沖刷與耐震觀點分析最低支出下壁式與構架式橋梁設計方法之比較

Abstract

橋梁耐震設計規範規定當地震發生時無論有無基礎裸露，橋梁基礎勢必要保持彈性，但此方法對於壁式與構架式新建橋梁設計而言並非相當經濟。因此本研究將以兩種方法設計橋梁，第一種方法是以橋梁耐震設計規範之靜力分析法進行壁式與構架式橋梁之設計，第二種方法則以載種組合對於橋梁下部結構基樁做設計，且依循規範將基樁加以圍束，並允許樁頂產生塑鉸。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之評估，最後再進行災損分析，求得新建橋梁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，再配合壁式與構架式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，因此將建立一裸露深度或然率分布曲線進行災損分析，最終比較二種方法之經濟性。

The Seismic Design Specifications for Highway Bridges specifies that the pier of the bridge must maintain its’ elasticity during an earthquake. However, this method is not very cost effective for wall pier bridges and bent bridges. Therefore, the study will provide two methods of bridge design. The first method is to implement static analysis according to the Seismic Design Specifications in designing wall piers and bent bridges. The second method is by load combination in designing the pile of bridge substructures. Increasing the stirrup allows the plastic hinge to occur at the top of the pile. Then by using the Capacity Spectrum Analysis (CSA) the designer can determine the method’s aseismatic capability and damage analysis. This creates a comparison of the two methods This study uses CSA to determine the seismic capability of different depths of base plane. The earthquake damage is divided into sections ranging from 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). Using the annual excess probability curve to correspond with the different PGA will simulate the seismic hazard curve based on the location of the bridge. The repair expenses of all of the levels will be calculated as a percentage of the cost of the new bridge. A probability curve is established in the exposed depth of the bridge location in order to begin the damage analysis. The probability curve uses the exposed depth in a year as a random variable. This report will compare the efficiencies of the two methods.