| Summary: | 博士 === 國立中興大學 === 土木工程學系所 === 106 === This study makes use of Rayleigh wave dispersion behavior to develop nondestructive test techniques for determining surface deterioration depth of concrete, detecting the depth of surface-opening crack and evaluating the quality of surface crack repair on concrete structures.
In the aspect of surface degradation depth detection, a stress wave is introduced into the test object by striking concrete with a small sphere, and a receiver is arranged on the striking surface to record the surface displacement reaction signal caused by the wave. The recorded waveform was converted into a spectrogram by Morlet wavelet transform to observe the dispersion characteristics of the R wave. Finally, use the Rayleigh wave velocity dispersion curve to obtain the surface degradation depth. The results show that when the receiver is far enough away from the striking point, the concrete plate with the surface weak layer will have a faster wave velocity as the R-wave wavelength increases, and the constructed dispersion curve has an obvious turning point showing the change of wave speed. The deterioration depth is 1.7 times the wavelength corresponding to the turning point.
In the aspect of surface-opening crack depth detection, the use of dispersion characteristics of the Rayleigh wave through the crack and the spectrogram of the Morlet wavelet transform is adopted. When wavelength is greater than the crack depth, Rayleigh Wave dispersion effect can be determined. When the wavelength is smaller than the crack depth, the R-wave can only transmit energy along the crack surface, and the wave transmission path is long then there is no dispersion effect. The corresponding wavelength at the turning point of the dispersion phenomenon is close to the crack depth. This frequency is defined as the cut-off frequency. This method can be used to estimate the crack depth and still be effective even in the case of the crack containing water.
In the aspect of crack Epoxy injection filling quality evaluation, the energy of the Rayleigh wave passing through the crack filling area is used as an evaluation benchmark. The higher filling ratio results in the larger transmission energy. In order to solve the problem that there may be a difference between the tapping energy and the receiver sensing energy during the test, the spectrogram self-calibration test method is adopted in the modified Morlet wavelet transform. The spectrogram amplitude can be effectively normalized, and the transmission function |TBC(f)| obtained after normalization is directly related to the Epoxy fill ratio. The higher the Epoxy fill ratio, the larger the value of |TBC(f)|. In practical, a complete non-cracking |TBC(f)| is used as the base for normalization. Numerical analysis establishes the relationship between normalization |TBC(f)| value and Epoxy filling ratio and the relationship can be used as the basis for practical tests. It is proven from the results of numerical analysis and experimental tests that the modified spectrogram self- calibration test method can effectively detect the crack Epoxy filling quality.
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