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

为了检测混凝土结构出现的裂缝或剥落部位，首先制作了10 mm ~ 40 mm深度的混凝土试块模拟裂缝，然后制作了2种厚度为20 mm的混凝土剥落试块，并对试验结果进行了分析。利用这些试块，对整个区域，特别是缺陷部位周围的振动响应进行了多次分析，结果发现，压电蜂鸣器装置在宽频率范围内激励振动是有效的，激光测振仪在振动观测方面也是有用的，对于剥离部分的检测，由于在音频范围内与声音部分相比，在该区域上存在强烈的振动响应，因此检测是容易的。对于裂纹的检测，在超声频率范围内，振动响应的幅值在槽的上方变得很弱。槽深超过20 mm时，测试槽两侧的相位延迟在超声频率范围内出现了数万度的大变化。对于实际检测技术而言，对测试面采用下压式加移动式激振装置是有用的，激光测振仪的双通道振动接收技术是获得稳定分析结果的有效方法，实际墙体表面的裂缝深度，从而得到有效的裂缝检测结果，但仅依靠这一阶段的分析技术，还不能清楚地识别裂缝深度的数量。于是，又尝试了另一种声音共鸣的方法。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.