Developing study of detecting method for defective part on concrete structure by using laser vibrometer.

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Vibration techniques were examined for detecting of crack or exfoliation part came put on a concrete structure.At first, some kinds of concrete test block with the groove of depth as 10mm-40mm were made for imitating cracks.Next, two kinds the concrete test block with exfoliation of thickness as 20mm were made. By using these test blocks, many analyzes of vibration response on the all area, especially around defective part, were carried out.As the result of these analyzes, it was found that piezoelectric buzzer device was effective for the excitation of vibration in wide frequency range.It was also found that laser vibrometer was useful for the observation of vibration, because it made easy positional moving and it had sensitivity in very high frequency range.As for detecting of parts of exfoliation, detecting was easy, because there was strong vibration response on such area compared with the sound part in the audio frequency range. As for detecting of crack, the amplitude of vibration response became weak over the groove in the supersonic frequency range. More than 20mm depth of the groove, phase delay in the supersonic frequency range appeared large changes as several ten thousand degrees between both sides of the test groove.For the practical detecting technique, pressing down type to the test surface and movable type device for vibration excitation is useful, and dual channel receiving technique for vibration by laser vibrometer was effective to obtain stable analyzed results.These techniques were also confirmed to the actual wall surface, and then effective results could be obtained for detection of the crack.By only these analyzing techniques in this stage, quantity of the crack depth could not be recognized clearly. So, another sound resonance method tried. Then, prospect of the quantitative detection of crack could be seen.