A Multiplicative Method and A Correlation Method for Acoustic Testing of Large-Size Compact Concrete Building Constructions

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New methods for acoustic testing of large-size (>1.5 m) concrete building structures (foundations, walls of buildings, airfield pavements, bridge pillars, slabs, blocks, beams, etc.) based on the use of methods of free and forced vibrations are reviewed. Problems of inspection of large-size concrete building structures by the resonance and the impact-echo method are considered. These methods are the only possible acoustic methods for testing large concrete building structures, that cannot be inspected by other (conventional) ultrasonic testing techniques. However, the resonance and impact echo methods for testing large-size concrete building constructions can be used only for testing extended building structures (in extended building structures the inspected thickness h is much smaller than the other dimensions). The resonance and impact echo methods cannot be used in compact building structures (in which the tested dimension, e.g., the thickness h, is comparable with at least one of the other dimensions), because of the influence of geometrical effects (the noise of the article shape does not allow unambiguous determination of the desired maximum in the article’s spectral characteristic). A new multichannel acoustic method for testing large-size compact concrete building constructions is considered. The method is based on the use of the resonance and impactecho methods with the subsequent multiplication of partial spectral characteristics. The multichannel multiplicative method allows performance of acoustic testing of large-size compact concrete building constructions (blocks, beams, columns, supports, and other standard articles). The second problem of inspection of large-size compact concrete building structures determined the necessity of calculating the acoustic velocity in compact articles. It is impossible to determine the acoustic-vibration velocity Cl in a compact article because of the effect of geometrical dispersion of the sound velocity. The resonance and impact echo methods can be used only at a known value of the correlation coefficient of the velocity of longitudinal vibrations in a particular compact article. This can be done using the technique of numerical simulation of acoustic fields. A new correlation method for determining the velocity in a compact article with known dimensions is described. It allows monitoring of the strength of arbitrarily shaped large-size compact concrete building constructions. Source: Wave Propagation in Materials for Modern Applications, Book edited by: Andrey Petrin, ISBN 978-953-7619-65-7, pp. 526, January 2010, INTECH, Croatia, downloaded from SCIYO.COM