Parametric analysis of the impact-echo phase method in the differentiation of reinforcing bar and crack signals

Abstract

The conventional impact-echo analysis applies the Fourier transform to the surface response of the target structure due to an impact of a steel ball. Then, the amplitude spectrum is used to determine the frequency of the echo signals. Although the amplitude spectrum may disclose the existence of an interface in the structure, it contains no information about the type of interface.This research group has proposed using the phase spectrum to differentiate reflections from cracks and reinforcing bars. Through numerical and physical tests, it was found that the phase of reflections at an air interface and reflections at steel interface fall within two distinct ranges, -π,π/4 and π/4,π, respectively.This study aims at examining the influence of the impact duration, the inclusion size/depth ratio, the sampling rate, and the sampling duration on the effectiveness of the impact-echo phase method. Numerical simulations and physical tests were conducted considering various combinations of impact sizes, inclusion sizes and depths, sampling rates, and sampling durations. The results suggest that the phase offset is an effective indicator of the inclusion type under the following conditions: (1) the product of the impact duration and depth frequency falls in the range 0.25,0.8; (2) the length-depth ratio of the crack exceeds 0.33; (3) the radius-depth ratio of the reinforcing bar exceeds 0.4; (4) the sampling rate exceeds 6 times of the depth frequency; (5) the product of sampling duration and depth frequency exceeds 33.3.