| Summary: | 碩士 === 朝陽大學 === 營建工程系碩士班 === 88 === Abstract
In this study the damages produced by corrosion of lattice-arranged steel rebars were evaluated by the impact-echo method based on the theory of stress-wave propagation. The relations among the corrosion rates corresponding to various rebar-size and cover thickness, the formation of delaminated crack, and the impact-echo responses were established. These relations and the database produced by the impact-echo results can be provided as the references for the future field tests. The test results were shown by the transfer functions which were calculated following the methodology formulated in previous studies. The results were discussed from the relations between the corrosion rates and the following three categories: the average amplitude and appearing rates of the steel responses, the average amplitude and appearing rates of the crack responses, and the average percentage of lost in plate-thickness frequency. The weight loses of the steel bar were measured using the standard method of ASTM G1-90 to calculated the corrosion rates.
The results shows most of the specimens producing delaminated cracks at the level of lattice-arranged rebar layer. Because the delaminated cracks are not necessarily occurred above the upper rebars, the steel responses may still be found in the spectra for the high corrosion levels. It is concluded to be no steel response when the transfer-amplitude at the steel frequency is below 0.3. The appearing rate of crack responses is about 90% in all the specimens when the corrosion rates reaches 1.0%. On the other hand, the transfer-amplitude of the crack response can reflect the severity of the damages for the delaminated crack. When the crack-amplitude is at the range of 0.4 to 0.5, the crack is only partially delaminated. In contrast, the crack is fully delaminated when the crack-amplitude is between 0.5 and 0.6. The plate-frequency is reduced 30% and 40% when the crack-amplitude is between 0.4 and 0.5, and 0.5 and 0.6, respectively. The plate-frequency is shifted even more when the flexure vibration occurs at the delaminated region.
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