| 摘要: | 發電廠傳輸電力至住宅或工商業區之過程，需透過輸電鐵塔進行電力傳輸，臺灣地貌變化大，輸電鐵塔常需建造於丘陵或山坡地區；以數值模擬分析結構穩定度時，通常以陣風作用於鐵塔上部結構的作用力為主要參數進行分析，針對地震力設計的規範則參考日本「送電用鐵塔基礎設計，第十三章，耐震設計」(2002) 進行基礎結構設計，基礎穩定性對於輸電鐵塔相當重要。
本研究進行一系列離心模型動態試驗，利用二階段離心模型縮尺律模擬輸電鐵塔A、B兩座重量分布不同但上部結構皆為60 m之輸電鐵塔，鐵塔坐落於土層相對密度85%的乾砂、軟岩及飽和地盤，其中包含水平及傾斜地盤，在40 g的穩定離心加速度場分別輸入1.8、0.4及0.2 Hz之主要振動事件，探討輸電鐵塔於不同地盤條件下受振動事件之動態反應。
試驗結果顯示，在乾砂地盤中鐵塔承受振動事件作用時，加速度放大反應較大；由於軟岩地盤能具有較高的圍束力，基礎穩定的狀況下不易產生加速度突波值，若振動事件沒有造成結構物共振，於乾砂地盤中的加速度放大倍率約為軟岩地盤的2倍，若振動事件造成結構物共振，於乾砂地盤及軟岩地盤之加速度放大倍率幾乎一致；在飽和地盤試驗中，若振動事件引致鐵塔共振時，於振動前期加速度放大反應較小，振動後期逐漸增大，後期約比前期反應大2倍；加速度相位差與振動事件頻率相關，在低頻與高頻振動事件中，輸電鐵塔A相對於基礎版A的相位差差異分別為55度和350度，輸電鐵塔B相對於基礎版B的相位差差異分別為12度和182度，由此可知振動事件頻率較高使上部結構的加速度相位差增加；於軟岩地盤中記錄到的彎矩值比乾砂地盤及飽和地盤小，因軟岩地盤提供基樁較大的圍束力，而上部結構之振動貢獻大部分的樁身彎矩值。
;Electricity conveyance beginning from the power plant to residential and industrial areas through the electrical transmission tower. Taiwan is covered by 70% of mountain area; therefore, the towers are usually built on slope. When analyzing the structure stability by numerical simulation, wind load is the primary parameter and not ground motion. Hence, the stability of whole structure subjected several ground motions will be studied.
In this study, series of dynamic centrifuge modelling tests were conducted to simulate two different electricity transmission tower models that have 60 m of height and different weights, which scaled by generalized scaling law. The superstructure models were placed on relative density of 85% sandy, saturated and soft rock stratum that is modeled by mixing silica sand and cement with 0% and 20% slope. Thickness of the center of soil deposit are 24 m and 40 m in prototype under 40 g-level for flat and slope ground, respectively.
From the results can be summarized that: (1) During shaking, the towers have obvious acceleration amplification reaction on dry sand stratum. There is no peak acceleration value recorded during shaking event, due to higher confining pressure from the soft rock stratum let the pile stable. If the shaking event cause the structure to resonate, the acceleration amplification factor in dry sandy stratum is two times soft rock stratum, in contrast, the difference of acceleration amplification factor is almost the same. If the shaking event causes the superstructure on the saturated sandy stratum to resonate, the acceleration amplification reaction is gradually increased. (2) The acceleration phase difference is related to the frequency of input motion. In S2 and S6 events, the phase difference of tower A is 350 degrees and 55 degrees, respectively, and tower B is 182 degrees and 12 degrees, respectively. It indicates that higher input motion frequency causes higher phase difference. (3) The pile bending moment in soft rock stratum is smaller than dry sand and saturation stratum, due to the higher confining pressure of soft rock stratum. Vibration from superstructure contributes the most of pile bending moment. |
