# Development of Track Support Stiffness Measurement and Evaluation System for Slab Tracks
## 3 Results and Discussion  
In this study, field tests were conducted to evaluate the performance of the TSS tester for the slab track and to evaluate the adequacy of the developed system and to evaluate the satisfaction of the performance requirements of the measurement and evaluation system. The performance requirement of the TSS tester is the appropriateness of the functional performance of the test equipment. For this evaluation, whether or not the system satisfies the test standards of railway standards (KRS TR 0014-15R) [11] for load control capability, dynamic excitation ability, and loading rate was examined. Furthermore, regarding the evaluation program that controls the test equipment as well as acquires, saves and post-processes measurement results, it was verified based on the operating performance of the test equipment. This was achieved using wireless communication if the control performance that met the normal operation and performance requirements of the test equipment was implemented. The main requirement of the track support stiffness evaluation system proposed in this study is the precision of the measurement to evaluate the static and dynamic spring stiffness based on the simultaneous measurement of the load and displacement. As a result, the relative error range of static and dynamic spring stiffness obtained by the TSS tester through wireless communication is analyzed to be less than 3% of the average value of the measuring result, which proved the adequacy of the control performance aspect of the TSS tester. Among the main performance indicators set in this study, the adequacy of the TSS tester (load control capability, dynamic vibration capability, and loading rate) is the control precision of \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Measured Results Using TSS Tester**} & \multicolumn{3}{c}{**Conventional**} & \multirow{2}{*}{**Design Value (Korean Standard)**} \\ \cline{2-2} \cline{4-11}
**Test Cycle** & & \multicolumn{3}{c}{**Static**} & \multicolumn{3}{c}{**Dynamic**} & \multirow{2}{*}{**Field Test Using Actual Vehicle**} & \multirow{2}{*}{**Design Value (Korean Standard)**} \\ \cline{2-2} \cline{4-11}  & **A** & \({}^{\star}\) & **B** & **A** & \({}^{\star}\) & **B** & **A** & \({}^{\star}\) & **C** & **D** & \({}^{\star}\) & **C** \\ \hline
1 st & 15.43 & 34.87 & (\(\sim\)2.09 & 17.10 & 38.41 & (\(\sim\)0.23 & & & (\(\sim\)3.50 & & (\sim\)4.79 \\ \hline
2 nd & 16.17 & 36.45 & (\(\sim\)2.60 & 16.98 & 38.16 & (\(\sim\)0.93 & 17.72 & 39.72 & (\(\sim\)4.18 & 17.5 & 40.24 & (\(\sim\)5.47 \\ \hline
3 rd & 15.68 & 35.42 & (\(\sim\)0.51 & 17.35 & 38.94 & (+1).23 & & & (\(\sim\)2.09 & & (\(\sim\)3.36 \\ \hline Ave. & 15.76 & 35.58 & 0.00 & 17.14 & 38.50 & (+0.07 & & (\(\sim\)3.27 & & (\(\sim\)4.56 \\ \hline \hline \end{tabular} \({}^{\star}\): Track support stiffness (kN/mm). A: Predicted spring stiffness (kN/mm). B: Relative error vs. average (%). C: Relative error vs. B (%). D: Design static spring stiffness (kN/mm).  
\end{table} 
Table 1: Comparisons of measured track support stiffness and predicted spring stiffness of resilient pad by testing methods. static and dynamic test loads and the excitation frequency implementation of the loading rate and dynamic excitation load (which as a sine function). In addition, a static load corresponds to a linearly increasing function that maintains a constant loading rate between the initial and maximum load values. This can be verified via field tests performed in this study to substantiate the adequacy of the load-history function. In most performance tests of elastic materials for the slab track, the static and dynamic spring stiffness of rail fastening system, which are obtained through laboratory tests, are generally tested only for resilient pads. In addition, even in the assembly test considering the rails and sleepers, the test specimen is very stable in terms of installation conditions, and the length of the rail applied to the assembly test is also short.