# Impact Evaluation of Track Girder Bearing on Yeongjong Grand Bridge
## 1 Introduction  
Bridge bearings applied to a railway bridge are installed on a bridge deck, and they need to have a means of generating resistance to negative reaction forces to support a track and rails installed on top of the bridge. The track should not be allowed to be rotated perpendicular to the bridge using bridge bearings in order to prevent falling of trains; however, even when small amounts of such rotations are permitted, it should be supported with considerable forces. In the case of a one-way movable end, stretching due to thermal strain, etc. should be allowed in the bridge axis direction. Bridge bearings include elastic bearings, steel bearings, pot bearings, disk bearings, spherical bearings, and seismic isolation bearings [1]. Line bearings are a type of steel bearing fabricated by casting for installation. They have a simple form, where one side of a junction is flat and the other is spherical for reduced frictional resistance and rotational displacement absorption [2]. Line bearings have a small bearing area for bearing support, which is likely to cause local damage to the bridge structure during load transfer. Further, these bearings have a short maintenance cycle owing to the wear of the joint, as all members that make up line bearings are made of steel [3]. These line bearings are used in a fixed end, in a movable end of less than 40 mm, or where the reaction force is not large. As they slide and move as per Hertzian contact theory, they suffer severe damage to the joint, and the friction coefficient may exceed significantly. Thus, it may be impossible to absorb and dissipate vibration generated during train operation, which may result in secondary damage such as train derailment caused by the transverse displacement of a track and rail surfaces resulting from the damage to a bearing block [4]. To solve such problems, research studies on bridge bearings are being actively conducted. [PERSON] et al. compared disk bearings with polyurethane (PTFE) disks by estimating the static and dynamic rigidity of the disk bearings through field tests and finite element analysis to solve the problems that occur in existing steel bearings. The static rigidity was found to be close to half of the estimated static rigidity under dynamic loading, and the dynamic behavior of the steel bearings turned out to be \(\sim\)80% greater than the dynamic rigidity of the disk bearings with PTFE. Further, the gap inside the expansion bearing seemed to play a critical role in increasing deformation [3]. [PERSON] and [PERSON] measured the dynamic behavior of line bearings, spherical bearings, and disc bearings of a railroad plate girder as a train traveled and analyzed the dynamic behavior of a plate girder bridge with each bearing. As a result, the results showed the highest dynamic behavior with line bearings, and there was a difference in the amount of lifting at fixed and movable ends with disc bearings. With spherical bearings, similar lifting amounts were measured at fixed and movable ends, confirming that spherical bearings had elastic resistance against lifting [5]. [PERSON] et al. applied train loads to a bridge with elastic bearings and conducted a numerical analysis of the shock. As a result, the dynamic response of the bridge remained constant, when damping effects were considered. When the elastic bearings were installed at the bridge point to isolate the seismic force, it was confirmed that the dynamic response of the bridge was adversely amplified against the moving train load [6]. [PERSON] and [PERSON] presented a simple model of fatigue and field measurements of the dynamic behavior of a railway bridge during the train service to analyze the complex elastic dynamic system. The cause of the dynamic effect on the fatigue of the bridge occurred in the vertical track position. The results of the study allow for the consideration of realistic dynamic amplification factors for fatigue verification [7]. [PERSON] et al.