High accurate detection of inclined cracks in concrete structures using an acceleration pickup

The present paper proposes a method for the detection of inclined cracks in concrete using an acceleration pickup. The sensor on the concrete surface observes the stationary waves inside the structure whose frequencies depend on the distance to the crack. The method can recognize the profile of the inclined crack with a high accuracy by the following two procedures. The 1st procedure : we model the sensor output as an output of a linear dynamic system with an unknown parameter and measure the accurate propagation distance from the sensor to the crack by applying a maximum likelihood method at each inspection point. The 2nd procedure : we apply a least squares method considering the reflection efficiency of the elastic waves at the inclined crack and the directivity characteristic of the sensor.