| Summary: | 碩士 === 朝陽科技大學 === 營建工程系 === 102 === The study is based on stress wave method to detect deterioration of concrete slab. The dispersion curves in frequency-slowness spectrum generated by Lamb wave modes of the slab are used for the assessment. The depth of the deterioration of the concrete slab is estimated by the wavelength - frequency diagram.
Using the displacement waveforms obtained by one impactor and one receiver, the group velocity dispersion curves, and then with the theory DISPERSE program get the solution to do comparative analysis.
Research to single concrete slab (wall), pure concrete slabs, and concrete surface layer composite panels and fire damage specimens, were tested and analyzed. Single concrete slab (wall) test results showed that the longer the distance, and then choosing a large source of percussion, the slowness spectrum would be more consistent with the theory of slow wave solution A0 mode. The group velocity can only be obtained for the wave with wavelength larger than 0.2 m. The velocity of shorter wavelength required shorten impactor-receiver distance.
The experimental results corresponding to the cement-concrete layered composite panel showed that group velocity is approximately constant for the wave with the wavelength of less than 1.5 times the thickness of the deterioration and closes to half of the P-wave velocity of the weak layer of cement paste for the cases with 0.06 m and 0.1 m thick weak layer.
For the specimen with surface damaged by fire, the results show that, the short wave-length waves are blocked by the surface cracks and is not obvious in the wavelength-velocity graph, unlike cement layered specimen where high-frequency energy can pass through the cement paste and induce signal of low velocity. The minimum wavelength of the wave with constant velocity is about 1.5 times the thickness of the deterioration.
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