This paper describes a method to estimate the position of a crack in a concrete block using several vibration pick-ups. An array of vibration pick-ups is attached on the concrete block, and a vibration pulse is forced by using a small hammer. If there is a crack, a reflection wave is generated from the position of the crack. Therefore, conventional methods to estimate the position of vibration source seems to be useful for this purpose. However, since the concrete block is elastic, there are three wave propagation modes; the surface wave mode, the primary wave mode and the secondary wave mode. Since the necessary primary wave mode is not significant in magnitude, we cannot estimate the position by the conventional methods. To increase the S/N, we had already proposed a method to eliminate the first-coming surface wave. However, the method was insufficient to achieve a higher S/N. Therefore, this paper proposes a new method to achieve a better location of a crack. Some experiments were carried out, and good results were obtained.
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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