# Impact Evaluation of Track Girder Bearing on Yeongjong Grand Bridge
## 2 Direct-Fixation Track Bearing System for the Yeongjong Grand Bridge  
The Yeongjong Grand Bridge is a composite bridge that extends over a total of 4.42 km, and it comprises a 0.55 km suspension bridge, a 2.25 km truss bridge, and a 1.62 km steel-box girder bridge as shown in Figure 1. The suspension bridge built in the main route is the first 3D self-anchored suspension bridge in South Korea for roads and railways [12]. The direct-fixation rail-fastening system (Figure 2) employed on the Yeongjong Grand Bridge is a rail-fastening system that uses a leaf-spring-type fastener, an adjustable pad as the adjustment packing, and a loosening preventive nut instead of a general nut [12,13]. Figure 3 shows schematic views of the direct-fixation track on the Yeongjong Grand Bridge. On the left and right sides of the Yeongjong Grand Bridge, line bearings are installed as shown in Figure 3a. The direct-fixation track is in a structure, where 12.5 m long simple-beam-type track girders are placed continuously to support the rail, as shown in Figure 3b. Figure 1: Scheme of s direct-fixation track on the Yeongjong Grand Bridge [12]. Figure 3: Schematics of the direct-fixation track system [12]: (**a**) cross-sectional view. 1. side bridge inspection passage, 2. center bridge inspection passage, 3. cross beam of the main bridge (truss and cable bridges); (**b**) side view. Figure 2: (**a**) Image of a direct-fixation rail-fastening system [12; 13]. (**b**) The composition of the direct-fixation rail-fastening system: 1. insulation block; 2. leaf-spring-type fastener; 3. bolt; 4. loosening preventive nut; 5. washer; 6. insulation plate; 7. rail pad; and 8. adjustable pad. As shown in Figure 3a, the bearing system was discussed with the direct-fixation rail-fastening system in a 12.5 m span installed. The top plate of the line bearing installed in Figure 3b transmits the vertical load and displacement acting on the structure to the low plate and only allows for movement in the bridge axis direction. In addition, the low plate is in direct contact with the top plate and accommodates vertical load and rotation. The structure of the line bearing installed in the Yeongjong Grand Bridge is as shown in Figure 4, and the installation status is as shown in Figure 5.  
As shown in Figure 6a, the line bearing easily cracks owing to the impact caused by the movement of vehicles [4,5]. Moreover, the end rotation causes the rail to be deformed, as the rail-fastening system is fixed directly to the bridge deck, and the vertical and compressive forces are generated at the end rail support points to support the rails. Figure 4: Scheme of the line bearing installed in the Yeongjong Grand Bridge. Figure 5: Installation status of the Yeongjong Grand Bridge line bearings. Figure 6: Damage of line bearings: (**a**) the line bearing type for replacement [5]; (**b**) the corroded top plate of the line bearing [4]. Cylindrical bearings transfer a vertical load and a vertical displacement acting on the structure to lower engineering plastic (EP) cylinders. By installing a device of resistance for a negative reaction force on the side, when the negative reaction occurs, it is transmitted to a side negative-reaction-prevention device to resist the load such as negative reaction and torsion. The vertical load transmitted by the top plate of the cylindrical bearing is passed on to the low plate stably by a central EP cylinder designed to be curved even when rotational displacement occurs. The central EP cylinder is designed in such a manner to minimize the friction coefficient of the contact surface. In addition, the side EP cylinder accommodates the load and displacement acting on the top and bottom locking devices installed on the side of the top plate to minimize the friction coefficient. The load can be transmitted, even if there is a rotational displacement of the top plate. Figure 7 shows the configuration of a plastic engineering cylindrical bearing (ECB), which is one of the cylindrical supports.