台灣中部地區橋樑檢測評估初步研究

Preliminary Study of Existing Bridge Inspection using Static and dynamic Plunking Test

呂健維(Chieh-wei Lu)

指導教授 ： 張子修

朝陽科技大學/理工學院/營建工程系/碩士(2010年)

摘要

本研究利用一般傳統靜態橋樑評估及動態敲擊實驗（Plunking Test）的方式探討橋梁承載、耐震能力安全評估工作。此試驗可以求得橋樑之震動衰減之幅度，並可以知道橋樑結構疲勞劣化是否會造成橋樑承載力和耐久性不足的問題。
本實驗結果顯示振動頻率會因為橋樑斷面尺寸及跨徑的差異而有顯著不同，尤其橋桁的支撐系統的不同亦會造成振動頻率及勁度K值的顯著差異。此外林尾大橋實驗所得之勁度K值均明顯大於靜載重試驗所得之K值，本研究認為此橋樑之靜載重試驗過程及結果可能須進一步確認其正確性及可用性。林尾大橋阻尼比值透過計算其值大於臨界阻尼，稱為超阻尼比（Over damped），此一超阻尼之橋樑在地震時可明顯抑制震動之產生。
一般混凝土結構物阻尼比值為5% ~7%之間，清元橋至今已經有28年的歷史，當年橋樑施工之品質管理欠佳且橋樑的老化會造成內部瑕疵或產生裂縫使阻尼比值增大，並且使其K值顯著降低；本實驗結果小於理論值（15~30%）似乎可以印證其老化及內部瑕疵之現象。

關鍵字：衝擊試驗、橋樑評估、橋樑勁度、阻尼比

關鍵字

阻尼比 ； 橋樑勁度 ； 橋樑評估 ； 衝擊試驗

並列摘要

The study was conducted to evaluate the structural integrity and earthquake resistance using commonly employed traditional method in bridge engineering and dynamic plunking test for the selected existing bridges in central Taiwan. The plunking test, which has been developed for several decades in structural dynamics, may provide additional information to reveal the existing structural conditions in terms of structural fatigue and material decay within the structural elements.
The results of the tests include the dynamic parameters such as stiffness k and damping ration D of the tested bridge girders to provide useful reference and guideline for the future repair/maintenance programs related to the structural capacity and durability of the bridges.
The results of the study revealed that the most significant factors affecting the natural frequency and stiffness is the bridge girder support conditions (boundary conditions: fixed, roller, hinge, free). Other significant factors include the cross-sectional dimension and span length of the bridge. The results of the study indicated that the damping ratio D of the tested Lin-wei bridge is close or equal to 1 which may imply the bridge exhibits critical or over damped behavior during strong vibration. In this case, the amplitude of the bridge during earthquake or vibration resonance condition may be significantly reduced and may provide more smooth traffic driving patters.
The results of the study also revealed that the stiffness k of the Chin-yuan bridge from tests is 15-30% less than the theoretical value. It is estimated that the significant reduction of the stiffness may be contributed to the quality decay of the bridge material and/or the long term lack of proper maintenance of the Chin-yuan bridge which was built about 80 years prior to the time of the bridge evaluation.

Keywords: bridge inspection, damping ratio, stiffness, plunking test

並列關鍵字

plunking test ； stiffness ； damping ratio ； bridge inspection

參考文獻

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(3)李有豐，“混凝土橋樑非破壞性檢測實例”，營建工程非破壞檢測研討會論文集，第133~163頁，民國86年1月。

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