Key points are not available for this paper at this time.
There is a high demand for a safe and cost-effective method to inspect the tightness of bolts remotely, which are widely used in power plants. Since it is known that rigidity decreases of a structure due to bolt loosening can be reflected in natural frequency of the structure, many methods for detecting bolt loosening through natural frequency have been proposed. However, most of those require the installation of contact sensors or markers, making them difficult to use when the main vibration point is at a high location. To overcome this problem, we utilized a video-based vibrometry technology which enables to measure vibration from a distance without any pre-installed sensors or markers and measured vibration of a substation's steel structure under impact excitation. The result suggested that the technology could remotely detect the decrease in dominant frequencies of the neighboring parts of intentionally loosened bolts, as well as the disappearance of the peaks.
Takada et al. (Sun,) studied this question.