本研究探討群樁基礎橋柱模型受沖刷後導致基礎裸露於近斷層地震作用下之受震反應。試驗採用雙軸向大型柔性邊界剪力試驗盒與長衝程高速度地震模擬振動台，砂土採用乾砂，其相對密度約為50 %，結構模型為2 × 2群樁基礎單柱結構，並於單柱頂部設置1.2 t鋼板質量塊以模擬橋梁上部結構，結構第一模態週期約為0.5秒，試驗共分為3中不同裸露深度分別為無裸露群樁(0D)、3倍樁徑裸露群樁以及6倍樁徑裸露群樁(6D)。試驗輸入白噪音得到了結構的主要週期，並通過3種具代表性地震獲取結構反應，試驗結果經由加速度規，位移計以及應變計等進行量測，並通過量測數據分析探討結構的加速度、位移反應以及應變趨勢等，數值分析方面採用分別採用等值線性土壤彈簧與美國石油協會(API)，並通過群樁振動台試驗進行比較與探討。
結果顯示隨著裸露深度增加，結構週期有延長趨勢,橋柱的應變極值，會隨著因裸露深度增加而降低，而群樁的應變極值位置會隨著裸露深度增加而改變，且大部分應變極值會出現在樁頂或3到12倍樁徑的位置，地震El Centro對結構造成影響比近斷層地震TCU068還大，主要與地表頻率內涵有關。數值分析則顯示採用API土壤彈簧與等值線性土壤彈簧(Proposed)在近斷層地震作用下對於質量塊加速度、位移歷時反應及基礎版加速度歷時反應皆有不錯的分析結果。

This study investigates the seismic response of a group pile foundation bridge model after scouring, which causes the foundation to be exposed during near-fault earthquakes. The test uses a Biaxial Shear Box and a Long stroke high-speed seismic simulation shaking table. The relative density of sand was about 50%. The specimen was a single pier structure supported by a 2 by 2 group. In total 1.2 tons of steel mass was placed on the top of the single column to simulate the superstructure of the bridge. The first modal period of the structure is about 0.5 seconds.
The scouring model fixed the specimen in the shear box and the model with a specified exposed length of pile foundation, as a ratio of pile diameter D, include no scour depth (0D) and 3 times scour depth (3D) and 6 times depth (6D). The experimental input white noise obtained the main period of the structure, and the structural response was obtained by three representative earthquakes. The test results were measured by acceleration gauge, displacement gauge and strain gauge, which were used to analysis the dynamic properties of the structure.
The results show that as the scour depth increases, the structural period has a tendency to increase. With the increase of scour depth, the maximum strain value of the bridge column will decrease, and the maximum strain value of pile will change position and transfer to another position. The maximum strain value will appear at the top of the pile or 3 to 12 times the diameter of the pile. The impact of the earthquake El Centro on the structure is larger than the near-fault earthquake TCU068, which is mainly related to the frequency content of the surface. Numerical analysis shows that the use of API soil springs and equivalent linear springs (Proposed) have good results in superstructure for near-fault earthquakes or general earthquakes.

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