# A Review and Future Directions on the Deterioration Evaluation of Concrete Utility Poles
## 4 The Current Studies of Wood Utility Pole
### Deterioration Evaluation of Wood Utility Pole  
More studies have been conducted on deterioration evaluation methods for wooden utility poles compared to concrete utility poles. Non-destructive testing (NDT) methods utilizing vibrations [48; 49; 50; 51; 52; 53; 54; 55; 56; 57; 58; 59; 60; 61; 62] involve propagating guided waves into the interior of utility poles using ultrasonic waves or impact hammers. The deterioration evaluation is conducted by analyzing the waveforms of the received guided waves, propagation speed changes, the utility poles' natural frequencies following the flow shown in Figures 4 and 5, and their vibration modes. Figure 4: Image and flow of evaluation methods by vibration acceleration due to guided waves. As an example, [PERSON] et al. [48] suggested the possibility of evaluating the embedded length of a utility pole and the degree of damage to the buried section from the propagation wave characteristics of ultrasonic waves propagated into the pole using Micro Fiber Composites for non-destructive inspection of defects in wooden utility poles. In the experiment, an MFC ultrasonic wave generator and sensor were attached to a wooden utility pole, The ultrasonic waves were measured to confirm the changes in the waveforms of healthy poles and damaged poles shown in Figure 6. It has also been confirmed that the measured waveforms can be decomposed and detected using CEEMDAN (complete ensemble empirical mode decomposition with adaptive noise) to more clearly confirm damage. [PERSON] et al. [49, 50] proposed a method for damage assessment, applying machine learning algorithms to perform pattern recognition and classification of statistically transformed measurement signals to perform damage classification for structural health monitoring (SHM) of wooden utility poles and to assess the health of utility poles, including embedded sections. They also proposed an automatic determination system based on this method. Regarding the problems with the current non-destructive inspection using guided waves, it can only pick up damage in the range where the guided waves propagate. Hence, the evaluation is localized, and it is difficult to evaluate the degree of damage. However, the presence or absence of damage can be evaluated. In nondestructive inspection using vibration [57, 58, 59, 60, 61, 62], the measured acceleration and displacement spectrum are analyzed to check the deterioration of the utility poles following the flow shown in Figure 5. If there is damage, the difference in vibration frequency and  
Figure 5: Image and flow of evaluation methods by natural vibration acceleration. Figure 6: Measurement method and detected waveforms in the experiment (**a**) and decomposed waveforms obtained using CEEMDAN (**b**) [48]. decay, which are obtained as vibration characteristics like those shown in Figure 7, can confirm the presence or absence of damage on the utility pole. For example, [PERSON] et al. [57] investigated the possibility of managing the condition of utility poles from the spectral peaks identified by the Fast Fourier Transform of data acquired from vibrating wooden utility poles. By comparing the frequencies obtained by Fourier transforming the acceleration measured by accelerometers installed on 15 wooden utility poles, it was confirmed that the frequencies obtained varied between healthy poles, poles with acceptable damage, and poles with severe damage. [PERSON] et al. [58] proposed a method using frequency modulation empirical mode decomposition (FM-EMD) to estimate the soundness of wooden utility poles from their vibration modes. In this method, multiple vibration modes from a wooden utility pole are decomposed into their respective single modes using FM-EMD to obtain the natural frequencies and decay coefficients, and the health of the pole is estimated from the obtained sticking frequencies and decay constants. Simulation models have also been used to assess applicability in non-destructive testing using vibration. For example, [PERSON] et al.