2024 Volume 5 Issue 3 Pages 823-833
To ensure safe and smooth road usage, it is necessary to appropriately detect abnormalities in road auxiliary structures, including road information boards. In this study, we conducted a year-long acceleration measurement on the road information board supported by type F pillars and analyzed the characteristics of the eigenfrequency of these boards over a long period. The results showed that even under normal conditions, the natural frequencies tend to change due to variations in the temperature of the steel material, which affects the performance of anomaly detection. To suppress the changes in natural frequencies caused by temperature variations, a correction method using simple linear regression was implemented, resulting in noticeable improvements. Next, we applied the Mann-Whitney’s U test to the time series of natural frequencies to detect their temporal changes. Unfortunately, many false positives were estimated because of the fluctuations of the natural frequencies. So, we estimated the cumulative distribution function of the Z-value in health condition and detected the abnormalities by evaluating the occurrence probability of the Z-value with the estimated function. The results showed that the change in natural frequency of 0.01 Hz was detected with 95 % accuracy.
