鋼筋混凝土內部缺陷之合成聚焦顯像法; A Synthetic Aperture Focusing Technique for Imaging Defects inside the Reinforced Concrete Element

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Title:	鋼筋混凝土內部缺陷之合成聚焦顯像法;A Synthetic Aperture Focusing Technique for Imaging Defects inside the Reinforced Concrete Element
Authors:	邱進隆;Chiu,Chin-Lung
Contributors:	土木工程學系
Keywords:	混凝土結構;缺陷;孔洞;彈性波;非破壞檢測;希爾伯特-黃轉換;影像;concrete structure;damage;void;elastic wave;non-destructive testing;HHT;image
Date:	2013-07-02
Issue Date:	2013-08-22 11:38:02 (UTC+8)
Publisher:	國立中央大學
Abstract:	運用彈性波檢測混凝土結構內部缺陷之方法眾多且已行之有年，但眾多的技術在早期檢測上的運用大部分是屬於點-線的檢測方式，檢測結果較為局部。而隨著計算機軟硬體的迅速發展，許多專家學者將彈性波搭配影像分析也逐漸發展成為一新的檢測技術。然而，這其中大部分的檢測方法均只針對純混凝土試體進行探討。而實際的混凝土結構物往往都有鋼筋的存在。因此，本研究即針對含有鋼筋的混凝土試體利用彈性波合成聚焦顯像法進行敲擊掃描研究。文中以暫態彈性波為基礎，結合合成聚焦顯像法，發展混凝土結構物內部缺陷顯像技術。在研究中均以有限差分法數值模擬，初步進行多個內含異質缺陷之混凝土試體進行敲擊訊號模擬及聚焦顯像，後續再搭配實驗，驗證該研究之可行性。在研究之初，先以單測面時間域之速度訊號進行聚焦顯像。在數值與實驗的結果中，均顯示不論是孔洞亦或是裂縫缺陷在純混凝土試體中均有不錯的顯像效果。文中亦深入探討鋼筋對於合成聚焦顯像法之影響，並成功定量出掃描影像與鋼筋-波長間的相互關係。接續，以先進的時頻域訊號處理方法(Hilbert-Huang Transform, HHT)，利用其可分析非線性及非穩態訊號之特點，並對於訊號中之不連續在時頻訊號上會有明顯頻率跳動之優勢，藉以凸顯檢測訊號中的缺陷反射訊號，進而獲得更佳品質的混凝土結構內部缺陷顯像。而就單一測面檢測時，顯像結果會導致缺陷資訊有所缺漏之問題。在文中提出了以多測面聚焦影像疊加來加以改善，能夠更加完整地呈現結構物內部缺陷資訊。並提出以影像重建之方法重新修正疊加影像，使檢測圖像辨識度大幅提升。後續，亦針對彈性波合成聚焦影像之影像品質進行探討。文中將影像品質區分為解析度與對比度兩種控制因子。並依據分析結果提出未來於現地實際運用時可依循之標的。最後，本文依據合成聚焦顯像法理論與操作方式，結合類比-數位轉換卡(A/D card)及筆記型電腦，架構一套混凝土結構內部缺陷檢測系統。配合圖形介面的硬體控制及訊號、影像處理程式之開發，縮減了運用暫態彈性波合成聚焦顯像法檢測混凝土缺陷之操作時程，使系統能夠有效率地應用於現地混凝土結構之非破壞性檢測。 This study combined with the transient elastic wave propagation theory and the synthetic aperture focusing technique (SAFT) to develop a method for imaging the defects inside the reinforced concrete structure. In the study, the finite deference method was used to simulate the stress wave propagation behavior in the concrete specimen with embedded defects and verified the results by the experiment. For most of the existing elastic-wave-based nondestructive testing methods, it is hard to detect defects inside reinforced concrete elements owing to the complex signals reflected from rebars. Therefore, this study conferred the possibility for using SAFT to scan and image the defects inside the reinforced concrete. In the first, the time-velocity curves were used to get an image by SAFT. The numerical and experimental images also show nice results can be obtained either holes or cracks inside the absolute concrete specimens. Next, the influence of the rebar on quality of SAFT image was quantitatively analyzed by a serious of numerical simulations. The experimental results show good agreements with the quantitative analyzing results. Then, the time-frequency analysis was further used to transform the original time domain signals. After the transform, the instantaneous frequency can occur an obviously hopping in the non-continuous of the signals. According to the property of HT, the reflection signal can be highlighted and get better SAFT image. This study also brought up to a multi-directional many-dimensional inspection technique to improve problem of the defect information missing in the one-directional inspection and used image reconstruct technique to upgrade the integrity of defect image. The image quality (resolution and contrast) of SAFT quality was qualitative analyzed by elastic wave theory and finite deference. From the analysis results, It is shown that this newly developed an inspecting procedure for in situ detection is fairly good. Finally, a hardware system for detecting and imaging the defects inside the reinforced concrete based on the SAFT theory and operation procedure was developed. Due to the integration of the hardware control of graphical interface and the signal and image processing program, the total time for SAFT detection is dramatically reduced. The system can be more suitable for in situ non-destructive testing of the reinforced concrete.
Appears in Collections:	[Graduate Institute of Civil Engineering] Electronic Thesis & Dissertation

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