墩前淤積對橋墩穩定性影響之研究

The effect of debris accumulation on the stability of bridge piers

李昊翰(Hao-Han Lee)

指導教授 ： 黃仲偉

中原大學/工學院/土木工程研究所/碩士(2014年)

https://doi.org/10.6840/cycu201400134

摘要

近年來因氣候變遷所造成的極端降雨常造成橋梁的破壞，而其破壞模式常導因於橋墩附近淤積之漂流物使橋墩沖刷以及橋體所受水流力產生加乘效果，進而影響橋墩或上部結構之穩定性。本研究目的在於量測墩前淤積物對於橋墩受力與沖刷的影響，其次利用結構監測資料評估橋墩在沖刷後的穩定性。本文透過單橋墩及全橋縮尺模型進行沖刷實驗，探討墩前淤積於不同流速及不同淤積面積之狀況下，對橋墩造成之影響以及與橋墩傾倒之關係，並根據實驗數據、數值模擬與文獻上之研究成果進行比較。研究結果顯示漂流物阻水面積與流速的增加，對橋墩的沖刷越明顯且增加對橋墩的作用力。另一方面，分析沖刷過程之微振訊號可發現結構主頻會隨沖刷深度增加而逐漸降低，而碎形維度於橋墩傾倒前會產生大幅下降之現象。

關鍵字

碎形維度 ； 墩前淤積 ； 水流力 ； 主頻 ； 橋墩沖刷

並列摘要

According to past reconnaissance reports on typhoons or floods, the failure of some collapse bridges could be resorted to debris accumulation. The debris increases the effective area of substructure components, which increase the hydraulic loads on the substructure of bridges. In addition, the debris also reduces the flow area and causes backwater upstream, which results in more severely scouring. The purposes of this research are to measure the hydraulic loads on piers and scouring depths of piers under different debris accumulation extents and flow velocities. Furthermore, the stabilities of piers are analyzed through short-term fast Fourier transform and fractal analyses for the ambient measurements of velocimeters. A series of small-scale single-pier models and full-bridge modes were conducted to examine the structural behaviors under different flood velocities and debris accumulation extents. The experimental results are then compared with those from numerical simulations and literature formulas. Our results demonstrate that the hydraulic loads and scouring depths of piers increase with increasing the flow velocities and debris accumulation. Moreover, the fundamental frequencies of piers from short-term fast Fourier transform decrease with increasing the scouring depths while the fractal dimension decreases dramatically before the pier is overturning.

並列關鍵字

Pier scouring ； Debris accumulation ； Hydraulic loads ； Fundamental frequency ； Fractal dimension

參考文獻

劉光晏、洪曉慧，2009，八八水災高雄及屏東地區橋梁勘災結果，國家地震工程研究中心簡訊，第七十二期。

王傳益、黃奕超、施漢鵬、鄭人豪，2011，變量流流況下非均勻縱列雙橋墩局部沖刷之研究，農業工程學報，第57卷第1期，第35-45頁。

張忠潔，2002，跌水沖刷與橋墩沖刷互動關係試驗之研究，國立成功大學水利及海洋工程碩士論文。

AASHTO, 2002, Standard Specifications for Highway Bridges, 17th edit, American Association of State Highway and Transportation Officials.

Dubuc, B., Quiniou, J. F., Roques-Carmes, C., Tricot, C. and Zucker, S. W., 1989, Evaluating the Fractal Dimension of Profiles, Phys. Rev. A, vol.39, pp.1500-1512.