## 4 Conclusions  
In this study, laboratory testing and field measurements were conducted to analyze the influence of the corroded rail pads of direct fixation tracks on the dynamic track response, and assess the necessity of corroded rail pad replacement in terms of spring stiffness of the rail pad according to the corrosion in marine condition. The conclusions are as follows:  
1) Soft pads are generally used for concrete track. However, the direct fixation track on the Yeongjong Grand Bridge uses hard pads. In this study, the bridge behaved flexibly without using a soft pad. Therefore, the use of hard pads did not affect usability. 2) There was no obvious change observed in the track support stiffness or in the dynamic track response according to the replacement of the corroded rail pads. This indicates that the corroded rail pads with high spring stiffness do not change the track support stiffness as they corrode. In addition, the difference in vibration due to the rail pad replacement was found to be insignificant. 3) As the results of laboratory testing (static, dynamic, and aging spring stiffness tests), it investigated that the rail pads of direct fixation track on the Yeongjong Grand Bridge were not significantly affected by load and temperature (as applied via the aging test). In addition, when tested in the aging test under more adverse conditions than the field conditions, the rail pads did not exhibit any significant changes in their spring stiffness. This confirms that the rail pads installed in the direct fixation track were not affected by corrosion (environmental conditions), or the loading period (passing tonnage) during their use. 4) As the rail pads of the direct fixation track in the Yeongjong Grand Bridge have adequately high spring stiffness values, they did not exhibit any response to dynamic wheel load due to passing trains; thus, even if a hard rail pad was used for the track on the Yeongjong Grand Bridge, the elastic behavior of the track was ensured according to the flexible bending behavior of the track type. This indicates that such rail pads were made of SBR materials that were not directly affected by the corrosion and the passing tonnage. Therefore, for the rail pads in this study, even though the rail pads were corroded in appearance, there was no functional problem, so it was not necessary to replace it. Furthermore, further studies are needed to measure and evaluate the deterioration caused by corrosion of the rail pads. Conceptualization, [PERSON]-Y.C. and [PERSON]-Y.L. ; formal analysis, J.-Y.C. ; investigation, J.-Y.C. and [PERSON]-Y.L. ; data curation, [PERSON]-[PERSON] and J.-Y.C. ; writing--original draft preparation, J.-Y.C. and S.-H.K. ; writing--review and editing, S.-H.K. All authors have read and agreed to the published version of the manuscript. This research received no external funding. The authors declare no conflict of interest. The authors declare no conflict of interest. References References References  
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* _[PERSON] et al. (2016)_ [PERSON] [PERSON]; [PERSON] [PERSON]; [PERSON]; [PERSON]; [PERSON] Evaluation of behavior of direct fixation track and track girder ends on Yeongjong Grand Bridge. _J. Korean Soc. Saf._**2016**, _31_, 45-51. * [PERSON] (2014) [PERSON] Qualitative Analysis for Dynamic Behavior of Railway Ballasted Track. Ph.D. Thesis, Technical University of Berlin, Berlin, Germany, 2014. * _[PERSON] et al. (2002)_ [PERSON]; [PERSON]; [PERSON]; [PERSON] Highway bridges, Appendix D. In _Corrosion Cost and Preventive Strategies in the United States_; Federal Highway Administration: McLean, VA, USA, 2002. * _[PERSON] et al.