## 4 Results
### Suggestion of Nonlinear Rotational Stiffness
In the third interval, the average rotational stiffness was the highest for the new specimens (2.110 kNm/rad), followed by the average rotational stiffnesses for the specimens with a seven-year reuse period (1.506 kNm/rad), a one-year reuse period (1.402 kNm/rad), and a four-year reuse period (1.200 kNm/rad). In the case of a trilinear model of the wedge joint based on combining and averaging the results for the new and reused specimens, the initial rotational stiffness was 22.475 kNm/rad (rotation angle \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Classification**} & \multicolumn{3}{c}{**K Value (kNm/rad)**} & \multicolumn{3}{c}{\(\beta\) **Value (rad)**} \\ \cline{2-7}  & **K\({}_{1}\)** & **K\({}_{2}\)** & **K\({}_{3}\)** & **\(\beta_{1}\)** & **\(\beta_{2}\)** & **\(\beta_{3}\)** \\ \hline Reused-4-1 & 25.788 & 3.093 & 0.744 & 0.023 & 0.072 & 0.317 \\ Reused-4-2 & 12.783 & 3.464 & 1.424 & 0.030 & 0.112 & 0.261 \\ Reused-4-3 & 15.960 & 3.238 & 0.510 & 0.028 & 0.094 & 0.353 \\ Reused-4-4 & 22.096 & 3.247 & 1.394 & 0.020 & 0.045 & 0.200 \\ Reused-4-5 & 13.498 & - & - & 0.027 & - & - \\ Reused-4-6 & 24.234 & 3.969 & 1.104 & 0.020 & 0.05 & 0.293 \\ Reused-4-7 & 23.755 & 3.015 & 0.904 & 0.021 & 0.089 & 0.287 \\ Reused-4-8 & 27.618 & 4.230 & 1.812 & 0.014 & 0.035 & 0.158 \\ Reused-4-9 & 20.761 & 6.509 & 1.321 & 0.025 & 0.038 & 0.15 \\ Reused-4-10 & 21.201 & 3.796 & 1.616 & 0.024 & 0.052 & 0.191 \\ Reused-4-11 & 26.203 & 6.039 & 1.170 & 0.015 & 0.044 & 0.166 \\ \hline Reused-7-1 & 19.016 & 2.715 & 0.821 & 0.025 & 0.140 & 0.210 \\ Reused-7-2 & 16.897 & 3.950 & 1.678 & 0.100 & 0.04 & 0.157 \\ Reused-7-3 & 25.424 & 2.872 & 1.391 & 0.015 & 0.101 & 0.197 \\ Reused-7-4 & 15.709 & 5.030 & 1.474 & 0.010 & 0.108 & 0.160 \\ Reused-7-5 & 10.428 & 3.636 & 1.539 & 0.023 & 0.057 & 0.238 \\ Reused-7-6 & & & & Not measured & & \\ Reused-7-7 & 16.652 & 2.750 & 2.150 & 0.025 & 0.051 & 0.160 \\ Reused-7-8 & 22.857 & 7.041 & 2.065 & 0.020 & 0.043 & 0.158 \\ Reused-7-9 & 14.237 & 3.445 & 1.602 & 0.028 & 0.120 & 0.199 \\ Reused-7-10 & 20.633 & 2.216 & 1.517 & 0.018 & 0.101 & 0.151 \\ Reused-7-11 & 17.368 & 2.772 & 0.827 & 0.040 & 0.123 & 0.180 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: _Cont._limit value: 0.022 rad), the rotational stiffness of the second interval was 4.705 kNm/rad (rotation angle limit value: 0.080 rad), and the rotational stiffness of the third interval was 1.577 kNm/rad (rotation angle limit value: 0.178 rad). The trilinear model of the new and reused specimens was compared with the trilinear model with the average values shown in Figure 15. It was found that the initial rotational stiffness of the wedge joint decreased as the reuse period increased. Compared to the initial rotational stiffness of the new specimens, the initial rotational stiffness was 89.5% for the specimens with a one-year reuse period, 80.7% for the specimens with a four-year reuse period, and 68% for the specimens with a seven-year reuse period. The trilinear model parameters calculated using the average values differed from those for the specimens with increasing reuse periods in the second and third intervals.