Nondestructive technique for estimating crack positions in a concrete structure by subtraction of the surface-wave component

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In this paper, we describe a method for estimating a crack position in a concrete structure using several accelerometers. An array of accelerometers is attached to the concrete structure and an impact is made on the concrete surface using a small impulse hammer. A reflection wave is generated from the crack position if a crack exists. Conventional methods for estimating the reflection point might seem to be useful for the detection of cracks. Because the concrete structure is elastic, however, it has three wave-propagation modes: the surface-wave mode, the primary-wave mode, and the secondary-wave mode. We cannot estimate the position using conventional methods because the necessary primary-wave mode is weaker than the surface-wave mode. To estimate the crack position precisely, we have already proposed two methods for eliminating the surface-wave and side-wall reflections. However, elimination using those methods was insufficient because they sometimes indicated a peak at a position where no crack existed. Therefore, in this paper, we propose a new method for estimating the surface wave more precisely to suppress such peaks. Some experiments were carried out, yielding better results.
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