# Performance of CRTS-II Ballastless Track-Bridge Structural System Rebars under Fatigue Loading Test
## 1 Introduction
The fatigue failure modes of heavy-load railway bridges, the variation laws of amplitude, stiffness, strain of non-prestressing bars and prestressing bars, and the concrete strain with the number of repeated loads are studied. The investigation shows that the stress amplitude ratio of the pre-stressed and non-pre-stressed bar before fatigue failure, which is caused by fatigue fracture of the non-pre-stressed bar at bottom of the beam of the heavy-load railway bridge, is about 0.6-0.7. [PERSON] [16] carries out a test and numerical analysis of the fatigue performance of the heavy-duty railway pre-stressed concrete beam under a constant and variable amplitude fatigue load, with emphasis on analyzing and fitting the residual strain of the concrete in the compression zone and gives the S-N relationships of the bottom tensile steel bar, related to the prestressing force. The test results show that the displacement and strain of the concrete and reinforcing steel in the compression zone of the beam under a variable amplitude fatigue test show a multi-stage development trend due to the increase in the multi-stage fatigue load. Combined with the multi-stage linear cumulative damage criterion, the fatigue characterization model of the tensile steel-rebar and pre-stressing steel strand is given. The existing literature only considers individual concrete bridges under the fatigue test. Moreover, there are few research studies on the mechanical fatigue of steel bars in the high-speed railway pre-stressed concrete track-bridges structural system. The fundamental difference between the ballastless track-bridge structural system and the single concrete bridge structure is that in the track-bridge structural system, the bridge structure and the ballastless track structure overlaid on it form an interactive and interdependent organic structural system [17]; the ballastless track structure restricts the deformation of the bridge to a certain extent [18]. Therefore, the fatigue characteristics of the steel rebars in the high-speed railway ballastless track-bridge structural system under a train load are different from the above research [19]. The stress level of the steel rebars in the girder under a train load is lower, indicating high-cycle fatigue. The failure probability under service conditions is insignificant. Existing studies mainly focus on the fatigue failure mode and fatigue life of pre-stressed concrete beams. There are few studies on the evolution of the mechanical properties of the steel bars in the beam under high-cycle fatigue loading. In this paper, a 1/4 scaled specimen of the whole track-bridge structural system was constructed, and an 18 million train-load fatigue test was carried out in the laboratory. The development of the strain, strain amplitude and slope of the load-strain curve of longitudinal steel rebars was monitored and used to analyze their fatigue behaviors. A finite element analysis method considering the fatigue damage of steel bars, and the concrete and cement-emulsified asphalt (CA) mortar is proposed to simulate the fatigue behaviors of steel bars in a ballastless track-bridge structural system during the fatigue damage stage; the calculated results are verified by the test results.