Influence of source frequency on impact-echo data quality for testing concrete structures

In impact-echo data, a correct interpretation of the measured frequencies may become a problem when in presence of a multitude of peaks in the spectra. An important evaluation criterion is then the magnitude of the measured peaks. This signal parameter is strongly influenced by the frequency components of the wave generated at the impact point. On-site measurements showed that, in particular cases, the wave centre frequency might have greater importance than the maximum usable frequency of the signal. Values of impact contact time, wave centre and maximum frequency in function of the impact source size were calculated from on-site data and from calibration measurements in the laboratory. The consequences for the planning of the tests and for a correct data interpretation are discussed. It was concluded that the expected measured frequency should be excited with maximum energy in the input signal in order to achieve an optimum quality of the data and ease data interpretation. (C) 2002 Elsevier Science Ltd. All rights reserved.