Paper Title
Frequency Characteristics Analysis of Elastic Waves Oscillated by Impact Devices for Impact-Echo Method and Application to Void Detection at Anchor Bolt in Concrete by SIBIE

Abstract
Impact Echo method is one of non-destructive testing (NDT) technique of concrete. Impact echo method is implemented in three stages such as applying impact using impactors, detecting stress wave and identifying peak frequencies of the signal. Various impactors has been developed for impact echo method to generate stress waves inside the media. To detect response of subject which stress wave affect, a laser vibrometer or an accelerometer is applicable. Peak frequencies are identified after Fast Fourier Transform (FFT) analysis of the signals. Since every impactor is producing different frequency range, characteristics of each impactors were investigated. In this study, calibrations were carried out by frequency spectrum comparison of these impactors. Moreover, the stack imaging of spectral amplitudes based on impact-echo (SIBIE) procedure was applied on plain concrete and concrete inserted anchor bolt for detection of the voids below anchor bolt inside concrete using single accelerometer. High intensity region were detected on concrete containing an anchor bolt and voids based on the result. Key Words - NDT, Impact Echo Method, SIBIE Procedure, FFT, Impactors.