近斷層效應對直接基礎橋梁受震行為之影響

橋梁係透過不同的基礎型式將載重傳遞到地下，由於土壤與地下結構僅能提供有限的束制能力，因此橋墩底部的勁度會低於理想固接支承下之邊界條件。結構勁度降低會導致橋梁基本振動週期變長，雖然對應之譜加速度可能減少，降低橋梁所受的地震力；但結構的側向位移同樣會因勁度降低而隨之增加，因此土壤－基礎互制效應對橋梁耐震設計而言相當重要。本研究利用套裝軟體SAP 2000建立直接基礎橋梁模型，利用土壤彈簧來模擬土壤－基礎互制效應，並以非線性動力歷時分析探討近斷層地震與設計地震對於直接基礎橋梁之影響；數值模擬顯示近斷層具有明顯之速度脈衝及永久殘留位移，因此設計時須考量地震特性所造成之影響，並在橋梁設計參數上加以修正。此外，本研究亦探討不同基礎尺寸及不同土壤彈簧力與位移關係對於橋梁受震反應之效應。數值模擬顯示基礎採用固接的方式可能錯估地震對橋梁之影響；採用多線段彈性或多線段塑性連桿元素來模擬土壤土壤－基礎互制效應更能貼近橋梁地震下實際行為，避免高估橋柱所需承受之地震力或低估柱頂最大位移。由於多線段模擬會增加計算所需時間，故本文提出利用單一可考慮基礎抬升效應之等值非線性旋轉彈簧模擬土壤－基礎互制效應，該等值彈簧可取代分佈之多個受壓不受拉間隙連桿，可減少計算時間且在設計上也趨於保守，適合工程界的採用。

關鍵字

近斷層；土壤彈簧；土壤─基礎互制；直接基礎；非線性動力分析

並列摘要

Loads for bridges are transferred to the ground through different types of foundations. Because the soil and foundations only provide limited restraints, the lateral stiffness on pier bottoms with foundations is lower than that in the ideal fixed boundary conditions. The reduction of the lateral stiffness of bridges may elongate the natural period of bridges and reduce the corresponding spectrual acceleration and seismic force of bridges. However, the lateral displacement of bridges may increase due to the reduction of lateral stiffness. Therefore, the effects of soil-foundation interactions are important in the bridge seismic designs. This study uses nonlinear time history analyses to investigate the seismic behaviors of bridges with shallow foundations under the near-fault earthquakes and design earthquakes while the soil-foundation interactions are modelled by the equivalent soil springs in the finite element package SAP 2000. Numerical results demonstrated that bridges with shallow foundations may be threatened under near-fault earthquakes due to the characteristics of the velocity impulse and permanent displacement. In addition, the influences of sizes of shallow foundations and the relationship between force and displacement of soil springs on the seismic behaviors of bridges are discussed. Numerical simulations show that the fixed boundary conditions may underestimate the responses of bridges. Furthermore, the soil-foundation interaction simulated by multilinear elastic and plastic link elements can provide more reasonable results. Finally, an equivalent gap element is proposed to simulate the soil-foundation interaction for bridges with shallow foundation. Numerical results indicate that the proposed method can save computational cost and provide a conservative design for bridges.

並列關鍵字

Near-fault, soil spring ； soil-foundation interaction ； shallow foundation ； non-linear dynamic analysis

參考文獻

27. 交通部，公路橋梁耐震性能設計規範草案複審成果報告書，2013。

33. 陳志宗，近斷層地震動的反應特性，台北科技大學土木與防災研究所碩士論文，2006。

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國際替代計量

近斷層效應對直接基礎橋梁受震行為之影響

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