台灣位處歐亞大陸板塊與菲律賓海板塊交界處,且地理位置常受到颱風的威脅,地震造成之慣性力、風力以及洪水沖刷都會對橋樑基礎造成側向荷載。沉箱基礎是國內橋樑工程中最常用的深基礎型式之一,但目前有關沉箱基礎之側向荷載行為研究不多,大尺寸之沉箱基礎側向荷載試驗數據相當稀少,關於沉箱塑性變形遽增之最大水平變位量目前仍無法確認。 本研究係利用國家地震工程研究中心於宜蘭縣蘭陽溪上,舊牛鬥橋橋址進行之現地大地試驗數據及舊牛鬥橋現地沉箱基礎側推試驗資料,探討沉箱受側向荷載時之反應及沉箱-土壤互制行為,並對現有規範中沉箱基礎之降伏狀態進行討論。 本研究主要分為三部份:先對現地平鈑試驗進行模擬,利用有限元素法軟體之Abaqus程式模擬卵礫石土壤之垂直、水平平鈑載重試驗,分析結果顯示,採用包含帽蓋之Drucker-Prager降伏模式能大致模擬卵礫石層之行為,並將分析歸納所得的土壤參數應用到沉箱基礎側推分析上。 接著對舊牛鬥橋沉箱基礎現地側推試驗進行模擬,採用三向度分析模型,並考慮沉箱與土壤間的互制關係,包括彼此之間可相互滑動及分離。經分析後發現模擬之結果與現地試驗結果接近,所建立之數值分析模型大致能模擬舊牛鬥橋現地沉箱基礎受側向荷載時之行為。 最後討論國內常用設計規範中定義沉箱基礎受側向荷載時之降伏狀態,並藉由舊牛鬥橋的數值分析模型,作進一步分析與探討。
Taiwan is situated on the convergent boundary between the Eurasian Plate and the Philippine Sea Plate. The location is frequently affected by typhoon, seismic inertia force, wind force and the floods will cause lateral load on the bridges foundation. Caisson foundation is a one of the most common types of deep foundation in bridge engineering. However, there were only few studies regarding lateral load effect on the caisson foundation. The test data in large scale in-situ lateral load test is even more limited. The maximum horizontal plastic deflection is still unable to confirm at present. This study used the data derived from the in-situ loading experiments geotechnical tests, and cyclic pushover tests on the old Nioudou Bridge in Ilan Country provided by the National Center for Research on Earthquake Engineering (NCREE) of Taiwan. Further investigation on the response of soil-caisson interaction and discussion the plastic state of caisson foundation were made. The study is divided into three parts, the first is using ABAQUS finite element software to simulate the vertical and horizontal plate loading test. The result indicated that using Drucker-Prager plasticity model with cap can almost simulate the act of gravel layer and the soil parameters derived can apply to caisson foundation analysis. Further stimulation test of the caisson foundation in Nioudou Bridge using the three dimensions model were carried out. The interrelationship of the caisson and the soil including the mutual slip and separateness. Analysis shown that the result of the stimulation is similar to the in-situ test, and the numeral analysis model established can almost simulate the behavior of the caisson foundation affected by the lateral load. Finally, further discussion of the definition of the plastic state used in the general design in the country of the caisson foundation through the numeral analysis of the Nioudou Bridge ,affected by the lateral load was also carried out.
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