# Development of Track Support Stiffness Measurement and Evaluation System for Slab Tracks
## 2 Overview of the Track Support Stiffness Evaluation System
### Development of Track Support Stiffness Measurement System  
The basic structure of the track support stiffness measurement system (herein referred to as TSS tester) for slab tracks is composed of actuator and body frame, as shown in Figure 12[2]. The core component of the TSS tester for slab tracks is the actuator that applies a load to the top part of the rail, as shown in Figure 12. This actuator can apply static and dynamic loads, and in the case of dynamic loads, the sine wave periodic load can be applied. Furthermore, the displacement response, according to the applied load, can be measured simultaneously so that the load-displacement curve can be obtained by measuring the load and the displacement simultaneously. In addition, a wheel-shaped jig connected with the actuator and the conforming pad on the rail face in the event of an uneven railhead was designed to eliminate the irregularity of load transfer and consider the real track in the field. The data storage device that controls the actuator of the measurement system and stores the measurement data signals can be controlled wirelessly, and the measurement data can be saved and handled by using the evaluation program (table PC) developed in this study without the need for separate configuration. The mobile bogie frame with two wheel-sets consisting of a conical tread with a rigid axle was devised so that the measurement equipment, which is a heavy object, can be easily moved and operated in the real field, as shown in Figure 13. The bogie frame consists of a special coupling device that can integrate the loading TSS tester (actuator and body frameset) into the mobile bogie. [2]. The coupling device is designed to move the body frame and actuator, that is, the horizontal (simultaneous measurement of both the left and right rails) and vertical movements of the TSS tester. Figure 14 shows the manufacturing view of the equipment accessories constituting the track support stiffness TSS tester [2]. The actuator with wheel rig (Figure 14a) that was the load-displacement measuring system was embedded in the center hole of body frame (Figure 14c). The body frame has two specially designed grip-type fixing points that can be fixed to the field rails an easily-removable pin in case of an emergency as is in a single system and, the frame comprises of a roller-type lateral movable fixing device for freely moving the left and right rails on the mobile bogie jig as shown in Figure 14c. Figure 12: Schematic of track support stiffness (TSS) tester components. As shown in Figure 14d, the mobile bogie frame is composed of a hydraulic motor (Figure 14b) that applies hydraulic pressure to the actuator, a control box that controls the hydraulic pressure and communicates wirelessly with the tablet PC, and a mobile bogie that can be placed on all these devices and the body frame [1]. The TSS tester weighs lesser than 8.896 kN; however, only components depicted in Figure 14a-c are considered as loads, and the bogie frame (Figure 14d) is exempted from this consideration. Thus, the total load value equals less than 0.588 kN. The track support stiffness  
Figure 14: Photograph of TSS tester components. (**a**) Actuator and wheel jig; (**b**) Hydraulic motor; (**c**) Body frame; (**d**) Bogie frame. Figure 13: Modeling of the TSS tester. TSS tester in this study combined with the body frame part and the mobile bogie jig is as shown in Figure 15[2]. The track support stiffness measurement and evaluation system for the slab track was a test run in the field to test the operability of the TSS tester using the mobility and the program of the track support stiffness TSS tester. In addition, communication problems between the TSS tester and the evaluation program were identified, and issues that may occur in the field and their solutions were examined.