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Nonlinear elastic wave spectroscopy (NEWS) is a package of advanced methods of ultrasonic spectroscopy which make it possible to capture with a high level of sensitivity the formation and development of structure damage even in materially, as well as geometrically, highly complicated specimens. Concrete and reinforced concrete are classical examples of materials to which the application of conventional ultrasonic methods is very complicated. This is why they make an ideal medium for the application of non-linear ultrasonic methods. The object of this experimental study consists of the application of nonlinear ultrasonic testing to assess the structural integrity of a reinforced concrete girder which was extracted from a bridge structure during the reconstruction of the bridge. The girder was tested in three stages: prior to loading, in the course of loading, and when the loading had been completed, with the aim of identifying the parameters correlating with the girder structure integrity damage. Two nonlinear ultrasonic spectroscopy methods were applied, namely, employing one and two harmonic signals. Frequency spectra of the transmission responses were analyzed. Defects occurring in the structure under investigation give rise to heavy nonlinear effects accompanying the propagation of elastic waves, which, in the singlesignal excitement case took effect in emphasizing the odd-numbered harmonic components among the newly generated frequencies. Therefore, the amplitudes of the latter were evaluated. In the other case, two ultrasonic signals of close frequencies were applied and their difference components were evaluated. Structure integrity damage was identified in the girder by means of the frequency spectrum analysis.

Monitoring of the Damage Evolution in Reinforced Concrete Girder by Means of Nonlinear Elastic Wave Spectroscopy