## 6 Test Results  
Figure 6 shows the results of the temperature experiment in the thermal chamber. At each level of temperature, the thermal strain becomes almost identical for both near the anchor head (o 140 mm circle) and the far side from the anchor head (o 180 mm circle). In order to investigate the strain difference, the averaged thermal strain of a o 140-mm fiber circle is calculated by the strains from 531 to 700 cm and the averaged strain of the o 180-mm fiber circle is also calculated by using the strains from 751 to 900 cm. In Table 1, these strain differences are shown due to temperature. The strain difference slightly increase with a temperature increase. This change is due to the incompleteness of the temperature test, which does not satisfy the temperature of the bearing plate that becomes uniform. Nevertheless, the maximum value of the strain difference, 17.16 microns, is acceptable in the field  
Figure 5: (**a**) Conceptual drawing of the bearing plate with a sensing fiber. (**b**) Experimental setup for a thermal strain measurement. (**c**) Anchor loading test by UTM (universal testing machine). because the anchor force, which is induced from this thermal strain difference, is small and also the temperature difference between the current and the initial measurement is to be much less than 70 \({}^{\circ}\)C. This represents that the thermal strain can be removed in the calculation of the difference between the two strains measured at the two locations (\(\omega\) 140 mm and \(\omega\) 180 mm circle). Thus, we confirm that Equation (2) is valid for applying the anchor force prediction by excluding the temperature effect, as explained in Section 2. Figure 7 shows strain distribution measured from the anchor tension test. The strain distributions at 10 different loading steps are presented in terms of the fiber distance. From the location of 410 cm to 607 cm, the optical fiber is wound about 4.7 turns and bonded at the \(\omega\) 140 mm circle location. The optical fiber from 620 to 810 mm is wound about 3.5 turns and bonded at the \(\omega\) 180-mm circle location. The strain valleys (maximum compressive strain) come from the direction toward the closest point on the edge of the bearing plate, and the strain peaks (minimum compressive strain) come from another edge of the bearing plate, similar to that in Reference [12]. Overall, the strain values at the \(\omega\) 140-mm circle are larger than those at the \(\omega\) 180-mm circle, and the variation in the strain distribution is larger at the \(\omega\) 180-mm circle than that of the \(\omega\) 140-mm circle. This represents that the deformation, due to the compressive force of the anchor head, increases toward the center of the bearing plate, while the geometry effect on the strain field increases as the distance from the center increases. After acquiring the signal output from OFDR shown in Figure 7, the average strain at the \(\omega\) 140-mm circle fiber is calculated using the data between 431 and 600 cm. In addition, the average strain at the \(\omega\) 180-mm circle fiber is determined by using the data from 651 to 800 cm. These average strains are shown with their strain differences due to anchor forces in Table 2. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Temperature (\({}^{\circ}\)C)** & **25** & **40** & **50** & **60** & **70** \\ \hline Strain at 140 mm & 210.23 & 373.18 & 477.78 & 589.25 & 707.50 \\ \hline Strain at 180 mm & 212.76 & 378.60 & 486.37 & 603.81 & 724.66 \\ \hline Strain difference & 2.54 & 5.41 & 8.59 & 14.56 & 17.16 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Difference between the averaged thermal strains at \(\omega\) 140 mm and \(\omega\) 180 mm on the bearing plate. Figure 6: Thermal strain distribution of the sensing optical fiber on the bearing plate.