本論文回顧了基本的斷層掃瞄理論，選擇較適用於土木結構的級數法作為理論依據來進行模擬分析，來判斷出鋼筋混凝土內部的鋼筋以及孔隙之位置。 震波斷層掃瞄理論由兩個部分組成，分別為正算模式部分與反算模式部分。正算模式決定波的行經路徑，而反算模式部分則根據這些波徑算出物體內部的波速分佈情形。本論文使用正六面體格點方塊模型，並利用線性走時內差(Linear Traveltime Interpolation Method, LTI)法作為計算波行路徑的方法。在反算部份則選擇速度分布之聯立疊代重建(Simultaneous Iterative Reconstruction Technique, SIRT)法作為搭配，結合成完整的斷層掃描理論。 由於實體模型需要大量的網格來組成，以現階段個人電腦的計算速度而言需要太過龐大的計算時間，因此本文採用數值模擬的方式來進行研究。研究成果顯示，三維斷層掃描法可以成功計算出試體內部的波速分佈，以及利用鋼筋混凝土組成物(鋼筋、混凝土與孔隙)之波速皆有其固定範圍的概念，可以大幅縮短計算時間並提高顯像之解析度。 In this paper, the series expansion method of computational tomography (CT) 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. A 3D least traveltime construction method is developed for all the nodal points in the wave propagation structure to a given source. The second is the inversion for updating the wave propagation structure constructed previously. The ray tracing technique, linear traveltime interpolation (LTI) method, is selected to combine with simultaneous iterative reconstruction technique (SIRT) to develop a three dimensional computational tomography scheme for reinforced concrete (RC) components. Numerical simulations verify that the accuracy and performance of this newly proposed 3D CT theory for RC components are acceptable. The convergent rate and image contrast of the CT calculation for RC component can be improved dramatically by taking the advantage that only three levels of wave speed, steel, concrete and void, are in a RC component. Once the calculated wave speed is close to a specific level, its value is enforced to set as the specific wave speed of the type of medium.
