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

研究了振动检测混凝土结构裂缝或剥落部位的技术。首先，制作了几种深度为10 mm~40 mm的混凝土试块来模拟裂缝；其次，制作了两种厚度为20 mm的混凝土试块。利用这些试块对所有部位，特别是缺陷部位进行了多次振动响应分析，分析结果表明，压电式蜂鸣器对宽频段的振动激励是有效的；激光测振仪位置容易移动，在很高的频率范围内灵敏度高，对振动的观察很有用；对于剥落部位的检测，容易检测，因为在音频范围内，与声音部分相比，该部位的振动响应较强。对于裂纹的检测，在超声波频率范围内，振动响应的幅值在凹槽上变得很弱。对于实际检测技术而言，采用压下式测试表面和移动式振动激励装置是有效的，激光测振仪双通道接收振动技术是有效的，并通过实际墙体表面进行验证，从而得到有效的裂纹检测结果，仅靠这些分析技术在现阶段还不能很好地识别裂纹的深度。于是，尝试了另一种声音共振方法。展望了裂纹定量检测的前景。

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.