應用希爾伯特-黃轉換之橋柱受沖刷之安全性實驗研究

Abstract

沖刷對於堤防設施、橋樑基礎等結構物之安全性監測是非常重要的議題之一，美國的統計資料中，受到水力造成之橋梁破壞高達六成，遠高於地震造成的3%，當橋梁不符使用條件情形下，對於生命財產、經濟發展都將帶來損失，若能事先規劃防範或預警，則可降低橋梁所影響之層面。本研究利用希爾伯特-黃轉換(Hilbert-Huang Transform, HHT)，分析結構受外力振動干擾下所測得訊號資料，利用固有模態函數(Intrinsic Mode Function, IMF)的瞬時頻率(Instantaneous Frequency, IF)與能量加權得到加權瞬時頻率(Weighted Instantaneous Frequency, WIF)，接著透過定義最大最小值(Maximum and Minimum value)、信賴區間(Confidence interval)、勁度比例(Stiffness ratio)三種方法界定加權瞬時頻率的範圍，由此進行橋梁健康狀態判定。為了驗證所提出的三種判定方法，本研究使用沉箱式基礎與群樁式基礎進行橋梁沖刷試驗，將橋柱逐步沖刷至傾倒並紀錄其上部結構震動歷時，同時進行即時數據處理。分析結果顯示，本研究可看出結構物行為上的改變，並準確地在橋柱傾倒前提供預警之功能。

Scouring issue is one of the most important topics in bridge health monitoring. In the US, the statistics showed that earthquake and scouring caused 60% and 3% of the bridge collapses, respectively. When bridges are under such harmful conditions, it will result in huge loss of human life and economic value. These situations indicate the importance of bridge health monitoring which can be used to diagnose the damage condition of structure before collapse. If warning in advance properly, the impact of the bridge collapse can be reduced. In this study, the Hilbert-Huang Transform (HHT) is used to analysis the measured signal from the superstructure. Firstly, the instantaneous Frequency (IF) of Intrinsic Mode Function (IMF) weighted with energy used to get the Weighted Instantaneous Frequency (WIF). By defining the range of Maximum and Minimum value, Confidence Interval (CI), Stiffness Ratio (SR), thereby the bridge health condition can be determined. In order to verify the proposed method, the scour tests by using caisson pile foundation and group pile foundation are conducted and examined. According to the analysis of the vibration signal recorded up to the time of collapse, it shows that the change of structure behavior can be rapidly reflected, and warning alarm before bridge collapse can be accurately provided.