斷層掃描(Tomography)是利用外來不具破壞性的探測能量，通過待測物體得到量測反應，藉由反應結果對待測物剖面進行成像的技術。本論文選擇以震波斷層掃描中的級數展開法作為理論基礎，其理論可分為正算模式與反算模式兩大部分。正算模式使用格點方塊模型搭配二維線性走時內差(Linear Traveltime Interpolation method, LTI)法作為計算波行路徑的方法。而反算模式則選擇速度分布之聯立疊代重建(SIRT)法反求待測試體斷面的波速分布。兩者搭配結合成一個完整的二維斷層掃描法。 對於土木工程結構物而言，由於鋼筋混凝土的高度非均質性造成應力波在試體內部傳遞行為複雜，會影響檢測結果的正確性及準確性。因此本文藉由數值模擬與實驗室試驗的方式進行研究。數值模擬方面，二維斷層掃描程式可以成功計算出試體斷面的波速分布，順利地對試體進行顯像。實驗室試驗方面，使用敲擊鎚做為應力波發射源，並採用壓電式位移探頭作為觸發裝置。根據前人研究之經驗，利用鋼筋混凝土組成物(鋼筋、混凝土與孔洞)之波速皆有其固定範圍的概念改善顯像解析度，研究成果顯示，可有效地將試體內鋼筋位置與孔洞分布情形顯現出來。Tomography is an inner image technique which generates a cross sectional picture of an object by utilizing the object’s response to the nondestructive, probing energy of an external source. In this thesis, the series expansion method of tomography was selected to develop a nondestructive evaluation technique for reinforced concrete components. In general, the tomography analysis contains two different procedures. The first one is the forward modeling for a given wave propagation structure. The forward modeling uses the ray tracing technique in order to simulate the curved ray path through the medium. The second is the inversion for updating the wave propagation structure. The ray tracing technique, linear traveltime interpolation (LTI) method which is selected to combine with simultaneous iterative reconstruction technique (SIRT) to develop a computational tomography (CT) scheme for reinforced concrete (RC) components. Numerical simulations verify that the feasibility and performance of this 2-D CT scheme for RC components are acceptable. In order to make the image more clear and improve the image contrast of the CT calculation for RC component, taking that only three levels of wave speed in a RC component: steel bar, concrete and void. In the laboratorial testing, an impact hammer is used to generate stress wave, and a piezoelectric displacement sensor is used as the trigger device for signal acquisition. Experimental results show that computed images also can identify the sizes and position of voids, the position of steel bar inside a simple RC component quite well.
