Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/13404
標題: 反射波走時法應用在混凝土構件之厚度量測
Application of the Time-of-Flight Reflection Technique to the Thickness Measurement of Concrete Elements
作者: 胡盟宗
Hu, Meng-Tsong
關鍵字: stress wave
應力波
time domain
frequency domain
impactor
時間領域
頻譜領域
敲擊源
出版社: 土木工程學系
摘要: 本論文之主要目的在於開發新的檢測技術,以作為混凝土版狀結構厚度之量測。不同於ASTM C1383法,於頻譜領域求得版厚頻率進而計算結構厚度,本論文以應力波動原理於時間領域訊號分析技術,探討版底反射P波動行為,利用位移波形中版底反射P波波到時間,及所量測版厚頻率或近距離反射波到時間,可同時計算求得結構厚度及P波波速。分別以數值分析與實際試體試驗,進行分析討論及試驗研究。研究結果顯示,當敲擊源與接收器配置距離達2.43倍版厚時,版底反射P波訊號得以判讀;當敲擊源與接收器距離很小時,由於表面傳動的P波、S波及R波遠早於版底反射P波到達接收器,在表面R波通過後造成能量衰減過程中,找到一向下位移波形,該向下轉折波形是為版底反射波到達之訊號,利用此一版底P波波到時間資料再配合遠距離的反射P波走時量亦可求得結構厚度。 由實驗的結果可以得到利用頻率及遠距離反射波、近距離及遠距離反射波兩種推算版厚的方法量測版厚,可以避免表面P波與內部P波相異造成版厚度量測誤差之問題;對於非版狀及泌水結構物則可以利用近距離及遠距離反射波推算構件厚度,以解除頻率因斷面邊界影響造成斷面厚度量測之限制。
The objective of this thesis is to develop new nondestructive techniques for determining the thickness of plate-like concrete structure. Unlike the method proposed in ASTM C1383 using spectral analysis, the techniques proposed in this thesis makes use of stress waves and signal analysis in time domain to get insight into the behavior of reflected P-wave, which travels into the structure and reflected from the bottom boundary. The thesis performs both numerical and experimental studies. Results obtained from the studies show that as the distance between the receiver and the impact point is longer than 2.43 times the plate thickness, the arrival of the P-wave reflected from the plate bottom surface can be identified. The first proposed technique is to combine the arrival time of the reflected P-wave with the thickness frequency obtained from the impact-echo test to measure the thickness of plate-like structures. In addition, if the distance between the impactor and the receiver is short, the stress waves propagating along surface such as P-wave, S-wave and R-wave arrive at the transducer earlier than the P-wave reflected from the bottom surface. When the R-wave arrives at the transducer it causes a relatively large downward displacement. However, the downward displacement caused by the arrival of the reflected P-wave is significant to identify in the waveform. Thus, combining the arrival time of the reflected P-wave for the case of short distance between the impactor and the receiver with that obtained from the far distance case offers the second proposed technique for determining the thickness of concrete structures. Results obtained from the experimental studies show that two proposed alternative techniques are feasible for measuring the thickness of plate-like concrete structures. The first proposed technique can be used to determine the internal P-wave speed and the accurate thickness of the concrete plate in the case of dissimilar P-wave speeds between the concrete surface and inside concrete. For non plate-like elements, using the second proposed technique based on time-domain analysis can eliminate the effect on the frequency response caused by close side boundaries of the concrete elements.
URI: http://hdl.handle.net/11455/13404
Appears in Collections:土木工程學系所

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