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Keywords: non-destructive testing, computerised tomography, acoustic attenuation, spectral frequency centroid downshift, stone masonry.

Summary

This paper illustrates the preliminary results of an experimental program to investigate the reliability of computerized attenuation tomography imaging in the diagnosis and characterization of building structures.

Computerized acoustic tomography is an emerging technique for advanced imaging of materials. The spatial distribution of the acoustic velocity and the attenuation are imaged and then correlated with properties directly related to physical conditions. The velocity depends on the elastic properties and density, while the attenuation is determined by the inelastic property of the medium. Experimental programs demonstrated that attenuation is more suitable than velocity to study the internal properties of materials. In fact, the wave's characteristics such as attenuation, scattering and frequency content may allow one to obtain relevant information about the material, because of the reliance of the propagation on the properties of the medium through which waves travel. Different materials absorb or attenuate the wave power at different rates, and waves are reflected by boundaries between dissimilar materials, so that changes in materials structure, e.g. presence of discontinuities or defects, can affect amplitude, direction, and frequency content of scattered signals. Following this trend, this study was focused on the attenuation tomography.

The attenuation tomography has been carried out on full scale stone masonry with a defect consisting of a macro-cavity. According to a model developed by Quan and Harris [1], a signal attenuation coefficient alpha₀ has been defined, and a statistically based method that estimates the attenuation coefficient from the spectral centroid downshift over a range of frequencies has been performed. The model states that the spectral centroid downshift is proportional to a path integral through the attenuation distribution and can be used as observed data to reconstruct the attenuation distribution tomographically. The tomographic problem has been implemented using the Matlab® software environment. Numerical modelling has involved an ill conditioned system of linear equations. The simultaneous iteration reconstruction technique (SIRT) has been implemented and applied to solve the system. The solution algorithm has been implemented in an automated procedure that allows the user to easily obtain a map of the attenuation distribution in the tomographic section. The LabView®'s native virtual instruments have been used.

The preliminary results showed that the computerized attenuation tomography imaging can successfully be applied to the stone masonry, and confirmed the suitability of the proposed approach to the non-destructive testing of building materials.

References

1: Y. Quan, J.M. Harris, "Seismic attenuation tomography using the frequency shift method", Geophysics, 62(3), 895-905, 1997. doi:10.1190/1.1444197

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Front Page Browse CCP CSETS CTR IJRT Other Authors Search Purchase Guide FAQ Contact us	Civil-Comp Proceedings ISSN 1759-3433 CCP: 91 PROCEEDINGS OF THE TWELFTH INTERNATIONAL CONFERENCE ON CIVIL, STRUCTURAL AND ENVIRONMENTAL ENGINEERING COMPUTING Edited by: B.H.V. Topping, L.F. Costa Neves and R.C. Barros Paper 155 Non-Destructive Testing of Stone Masonry using Acoustic Attenuation Tomography Imaging G. Concu¹, B. De Nicolo¹, C. Piga² and V. Popescu³ ¹Department of Structural Engineering, University of Cagliari, Italy ²Department of Land Engineering, University of Cagliari, Italy ³Department of Electronics, University of Transilvania, Romania doi:10.4203/ccp.91.155 purchase the full-text of this paper Full Bibliographic Reference for this paper G. Concu, B. De Nicolo, C. Piga, V. Popescu, "Non-Destructive Testing of Stone Masonry using Acoustic Attenuation Tomography Imaging", in B.H.V. Topping, L.F. Costa Neves, R.C. Barros, (Editors), "Proceedings of the Twelfth International Conference on Civil, Structural and Environmental Engineering Computing", Civil-Comp Press, Stirlingshire, UK, Paper 155, 2009. doi:10.4203/ccp.91.155 Keywords: non-destructive testing, computerised tomography, acoustic attenuation, spectral frequency centroid downshift, stone masonry. Summary This paper illustrates the preliminary results of an experimental program to investigate the reliability of computerized attenuation tomography imaging in the diagnosis and characterization of building structures. Computerized acoustic tomography is an emerging technique for advanced imaging of materials. The spatial distribution of the acoustic velocity and the attenuation are imaged and then correlated with properties directly related to physical conditions. The velocity depends on the elastic properties and density, while the attenuation is determined by the inelastic property of the medium. Experimental programs demonstrated that attenuation is more suitable than velocity to study the internal properties of materials. In fact, the wave's characteristics such as attenuation, scattering and frequency content may allow one to obtain relevant information about the material, because of the reliance of the propagation on the properties of the medium through which waves travel. Different materials absorb or attenuate the wave power at different rates, and waves are reflected by boundaries between dissimilar materials, so that changes in materials structure, e.g. presence of discontinuities or defects, can affect amplitude, direction, and frequency content of scattered signals. Following this trend, this study was focused on the attenuation tomography. The attenuation tomography has been carried out on full scale stone masonry with a defect consisting of a macro-cavity. According to a model developed by Quan and Harris [1], a signal attenuation coefficient alpha₀ has been defined, and a statistically based method that estimates the attenuation coefficient from the spectral centroid downshift over a range of frequencies has been performed. The model states that the spectral centroid downshift is proportional to a path integral through the attenuation distribution and can be used as observed data to reconstruct the attenuation distribution tomographically. The tomographic problem has been implemented using the Matlab® software environment. Numerical modelling has involved an ill conditioned system of linear equations. The simultaneous iteration reconstruction technique (SIRT) has been implemented and applied to solve the system. The solution algorithm has been implemented in an automated procedure that allows the user to easily obtain a map of the attenuation distribution in the tomographic section. The LabView®'s native virtual instruments have been used. The preliminary results showed that the computerized attenuation tomography imaging can successfully be applied to the stone masonry, and confirmed the suitability of the proposed approach to the non-destructive testing of building materials. References 1 Y. Quan, J.M. Harris, "Seismic attenuation tomography using the frequency shift method", Geophysics, 62(3), 895-905, 1997. doi:10.1190/1.1444197 purchase the full-text of this paper (price £20) go to the previous paper go to the next paper return to the table of contents return to the book description purchase this book (price £140 +P&P)
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