# An Improved Hilbert-Huang Transform for Vibration-Based Damage Detection of Utility Timber Poles
## 4 Experimental Program
### Testing Specim  
Field testing is executed on three serviceable and three unserviceable in situ utility timber poles located at Benalla, Victoria. Detail of the testing specimen is given in Tables 3 and 4.  
The data related to these 6 were collected on the same day and from the same geographical location, as mentioned in Tables 3 and 4. Condition of these poles were determined by the asset inspector from Ausnet Services using dig and drill method. Figure 7 demonstrates pole inspection below ground line using dig and drill method. Usually, 300 mm deep excavation is done around the pole. Then, ground inspection holes are drilled to the centre of the pole at an angle of 20 degree between ground line and 150 mm from the ground line (see Figure 7). This method is undertaken in the suspected area in order to allow measurement of internal deterioration and amount of sound wood. If sound wood measurement is below 30 mm, pole is considered as unserviceable, whereas measurement above 50 mm is considered as serviceable; also, measurements between 30 mm and 50 mm are considered as having a limited service life.  
### Testing Specim  
Figures 6 and 8 demonstrate the experimental field set up for the vibration testing. Hammer impact was induced at a height of 1500 mm on the side of the pole with an angle of 45\({}^{\circ}\). The sampling frequency was set to 100 kHz. Each pole was struck four times. Accelerometers were attached on the pole at 1200 mm and 900 mm from the ground level. Six accelerometers that are located at 1200 mm from the bottom of the pole are designated as layer 1 accelerometers and the other six accelerometers that are located at 900 mm from the bottom of the pole are designated as layer 2 accelerometers. For each accelerometer location,  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Unserviceable Pole 1** & **Unserviceable Pole 2** & **Unserviceable Pole 3** \\ \hline Timber species & White Stringybark & White Stringybark & White Stringybark \\ Timber type & Hardwood & Hardwood & Hardwood \\ Cross section & Circular & Circular & Circular \\ Strength class & 3 & 3 & 3 \\ Durability class & 2 & 2 & 2 \\ Condition of the pole & Unservicable/unhealthy & Unservicable/unhealthy & Unservicable/unhealthy \\ Dlamerer & 890 mm & 750 mm & 1100 mm \\ Above ground height & 9144 mm & 9910 mm & 15,240 mm \\ Location & Benalla, Victoria & Benalla, Victoria & Benalla, Victoria \\ Chemically treated & yes & yes & yes \\ timber & yes & yes & yes \\ \hline \hline \end{tabular}
\end{table}
Table 4: Detail of three unserviceable timber poles.  
Figure 7: Pole inspection below ground line using dig and drill method.  
three positions along the circumference \(0^{\circ}\), \(90^{\circ}\), and \(180^{\circ}\) were taken into account. The accelerometer which is aligned with the impact line is named as \(0^{\circ}\) and the accelerometer opposite to \(0^{\circ}\) is called \(180^{\circ}\). In the same way, the accelerometer which is located \(90^{\circ}\) around the circumference is called as \(90^{\circ}\). Additionally, at each accelerometer position, the displacement was captured in two orthogonal directions, i.e., in the longitudinal (L), radial (R) for \(0^{\circ}\) and \(180^{\circ}\) and longitudinal (L) and circumferential (C) for \(90^{\circ}\). The illustration of every accelerometer is named such a way that it represents the location and orientation of that particular accelerometer. For instance, a notation \"A90C1\" means the accelerometer belongs to layer 1 that is located at 1200 mm from the bottom of the pole and the position is \(90^{\circ}\) around the circumference; also, the displacement component is the circumferential one.