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中文標題: 河川橋梁之洪水下穩定性能研究(II)
英文標題: Stability Analyses of Cross-river Bridges under Flood Water and Debris Loads
編號: NCREE-12-023
語言: 中文
編輯:
媒體型式: 紙本
作者:
洪曉慧   陳筱安   黃仲偉   
中文摘要: 本研究旨在探討河川橋梁在颱洪狀態下受水流力作用之穩定性。台灣
地區河川坡陡流急,每當颱風挾帶豪雨來襲時,常會對橋墩基礎附近產生
局部沖刷,加重基礎裸露程度,而颱風與高速行進之水流與浮木也會對橋
體與裸露之基礎作用不小的水平力,進而危及橋梁整體之安全與穩定性。
此外,依據過去勘災經驗,已證實橋墩或上部結構附近淤積之漂流物會使
橋體所受之作用力產生加乘效果,工程師需仰賴可靠的分析步驟估計此等
作用力,才可合理地評估橋梁之安全性。有鑑於此,本研究擬結合分析與
試驗探討橋梁結構在不同流速、水深、基礎裸露深度與不同程度漂流物淤
積狀態下之耐洪能力。本計畫擬分三年進行。本報告綜整第二年之研究成
果,內容包括實驗與分析兩部分。實驗部分針對沉箱基礎橋墩之單墩進行
洪水下穩定試驗,以不同尺寸之木板模擬漂流物淤積於墩前之情況,實驗
結果證實漂流物淤積對橋墩穩定性之不良影響。分析部分以ABAQUS 有限元
分析軟體針對實驗所設計之單墩沉箱基礎進行驗證,考慮之參數包括水流
速度與漂流物淤積之範圍等,分析結果間接證實當墩前淤積物越大時,橋
墩底部的沖刷會越嚴重。
英文摘要: The purpose of present study is to investigate the stability of cross-river bridges subject to hydraulic loads, debris accumulations and impacts under extreme flood events. Steep riverbed and rapid flow are the common characteristics of Taiwan’s rivers. The heavy rain brought by Typhoon often induces local scouring around bridge foundations, and make the exposure of foundations more serious. According to past reconnaissance reports on typhoons or floods, the collapse of many bridges can be contributed to debris accumulation. The debris not only increases the effective area of substructure components, but also reduces the flow area and cause backwater upstream and increased velocities through the bridge opening. However, this effect of debris accumulation is not included in current bridge design code in Taiwan. In order to gain better understanding of bridge behavior in an extreme flood event, the hydraulic loads has to be calculated precisely, especially the hydraulic loads under the condition of debris accumulation. Therefore, a three-year project focusing on the flood-resistance of bridges is proposed. In order to examine the bridge structure behavior in different flood velocity, water level, level of foundation exposure, and debris accumulation extent. In the second year, a series of small scale hydraulic model tests and stability analyses of cross-river bridges under flood water and debris loads was conducted. In this experiment, planks of different sizes were used to simulate the debris accumulation of different levels. In addition, finite element analysis was also performed to investigate the effect of debris accumulations. The experiment confirms that debris accumulation can increase the hydraulic loads applied on the piers. Also, both experiment and analysis confirm that the debris accumulation can increase local scouring around bridge foundations.
關鍵字: 墩前淤積、沖刷、水流力
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