| Summary: | 碩士 === 國立中興大學 === 土木工程學系 === 91 === In the safety evaluation of concrete constructions, cracking is always one of the conditions that can’t be neglected. The Time-of-Flight Diffraction Technique offers a direct way of stress wave propagation to determining the depths of surface opening cracks; while applying stress wave propagation method to determining the surface crack depths on the concrete constructions, the depths of cracks and measurement of wave speeds all rely on the accurate analysis of displacement waveform in time domain. If one can’t effectively control the variations of stress waves, then the surface crack depths determining work will become more time and effort consuming. To let examiners effectively understand stress wave propagation while carrying out the experiment in place, the content of this thesis specifically describes the different shallow surface crack depths that were confronted in the experiments, hoping to provide references to following researchers on this related field. The research methods applied here are numerical analysis and laboratory studies experiment research. The stress wave was generated by impact, with the receiver equipped on the other side of the surface, one can monitor the stress wave propagation information. Through the control of the impact contact time and energy, one can have a comprehension on the allocation of the experiment and the wave variations caused from different surface crack depths. It is found out that the outcome experiment result are very consistent with those obtained from numerical analysis. When the depth of simulated cracks is more than 20.7mm, it becomes difficult for us to differentiate surface R wave from the wave figure. However, the upward movement tendency caused by the bottom part crack wave is highly increased and this kind of reflection adds the advantages to the examining work. Furthermore, according to the equipments needed in the experiment, error analysis was performed to investigate the influence of equipment allocation errors. From the experimental result, it is shown that the position error form H0 has profound influence on the result of crack depth measurement.
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