| Summary: | 碩士 === 國立中興大學 === 土木工程學系 === 90 === The application of the impact-echo method to detecting cracks with depths less than 0.5 m is satisfactory. For mass concrete structures, cracks may be much deeper than 1.0 m. The impact energy of normal steel spheres with diameters less than 18 mm is not enough to generate clear signals, which may result in significant measurement errors. The objective of this thesis is to develop a signal processing technique for deep crack measurement. The proposed technique makes use of superposition of signals obtained from repeated tests to enhance the signal amplitude of the wave arrival. It is expected to overcome the weak signal problem to increase the accuracy of deep crack measurement. In addition, the signal superposition technique is also applied to the measurement of cover thickness of reinforcing bars in concrete.
Experimental studies were carried out on a mass concrete specimen containing a simulated crack having a depth of 2.91m and on a concrete specimen containing reinforcing bars having cover depths of 0.09 and 0.10 m. Experimental results show that the signal, which is weak in a single test, is significantly increased after 5 times superposition of waveforms obtained from the repeated tests. The measurement results based on signal superposition are in good agreement with the known values. This demonstrates the feasibility of the proposed signal superposition technique.
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