## 1 Introduction  
One of the main components in concrete track systems is the rail pad, which is installed between the rail and the sleeper to attenuate wheel/rail interaction loads This prevents the underlying railway sleepers from experiencing excessive stress [1]. Soft pads are typically used for concrete tracks. However, the direct fixation track on the Yeongjong Grand Bridge uses hard pads. The direct-fixation track is the earliest form of track without ballast. This direct fixation track exhibits integrated behavior because the rail and track girder are rigidly connected together by the direct fixation rail fastening system. Moreover, the direct fixation track system of the Yeongjong Grand Bridge is attached to a long-span special bridge (cable and truss); this concept originated from the track style of the Great Seto Bridge in Japan [2, 3]. It is the only such track type in South Korea, and currently condition assessments and maintenance of this track are challenging [2, 3]. Other general types of direct fixation tracks have been widely deployed in recent years, and maintenance instructions will be required in the future. An important issue in the maintenance of both concrete slab tracks and direct fixation tracks is the timely replacement of the rail pads, commonly known as elastic pads (i.e., resilience pads and rail pads) [4]. As shown in Figure 1a, the track system on the Yeongjong Grand Bridge is installed with a direct fixation rail fastening system on upper flange of the track girder. Moreover, as shown in Figure 1b, it is continuously arranged with simple supported beam-type track girders with a length of 12.5 m for supporting the rail. The rail weighs 60 kg with rail supporting point spacing of 0.625 m and the direct fixation track has a design speed of 110 km/h. The rail fastener of the direct fixation track is applied with a flat spring joint, a rail pad (SBR, styrene butadiene rubber), an adjustable pad, and the anti-loosening nut as shown in Figure 1a [2,3]. In the previous research, it was estimated that the annual direct cost of corrosion in highway bridges in 2002 was $8.3 billion, with indirect costs to users due to traffic delays and lost productivity, estimated to be 10 times. A significant portion of that cost can be tied directly to replacement costs for bridge decks, which are damaged principally due to corrosion of reinforced steel caused by deicing  
Figure 1: Schematics of the direct fixation track system. (**a**) Direct fixation rail fastening system 1. insulation block, 2. leaf spring, 3. bolt, 4. anti-loosening nut, 5. washer, 6. insulation plate, 7. rail pad, and 8. adjustable pad; (**b**) side view of the track girder; and (**c**) cross section of the track girder [2,3]. chemicals, primarily sodium chloride and calcium chloride [5,6]. Deterioration of bridge decks is a primary factor limiting the lifespan of bridges especially in cold climates where deicing salts are commonly used. While controlling deck cracking or decreasing the permeability and porosity of concrete can improve the performance and service life of bridges, chloride, and moisture ingress as well as cracking cannot be completely eliminated. Full-depth cracks, which are caused by restrained shrinkage, lead to corrosive conditions at early ages for both the top and bottom reinforcement mats [7]. According to a study by [PERSON] et al., the use of stainless steel elements as bridge deck reinforcements in a critical situation significantly increased the initial cost but significantly reduced the overall life-cycle cost, making it cost effective in the long term [8]. In this study, the rail pad has a laminated structure. The upper surface is made of stainless steel and the lower surface is made of SBR material. SBR has a good abrasion resistance and good aging stability when protected by additives [9]. The stainless steel on the top surface is in contact with the bottom of the rail and the SBR at the bottom is in contact with the adjustable pad.