#### 1.1.4 Study on Fatigue Analysis of Slab-Type Track Structure  
Under fatigue loading, the prestressed steel rod of the track slab often fractures. In addition, a common problem of channeling occurs in the applications of CRTSI and III slab ballastless tracks. During the fabrication, transportation, and installation of the track slab, the track slab is subjected to external forces that make the corners or edges break and cause the appearance of small cracks along the lower border of a conventional base plate frame. Some of the cracks, after initiation, can progress into various areas of the base plate. Consequently, the cracks cause the base plate to eventually fracture, thereby impacting on the safety and service life of trains [29]. Due to the shrinkage and creep of the ballastless track, the vibration caused by the train's dynamic load, the sudden drop in the external environment temperature, and the uneven distribution of the water-cement ratio of the track slab, corrosion of the steel bar and the carbonization of the concrete occur in service. This has an impact on the durability of the structure. Due to the fact that the track slab is prefabricated with reinforced concrete with different tensile and compression properties, under the effect of overall cooling or negative temperature gradient, the track slab is prone to micro-cracks [30]. After the appearance of these cracks on the track slab, long-term exposure to the forces of weathering in the environment cause the concrete to peel off. The infiltration of rainwater into the cracks also significantly increase the stress level at the crack tip, which accelerates the deterioration of the base plate, which negatively impacts on the service life and performance of the base plate. The concept of fatigue damage can be understood as the material's performance attenuation under the action of load cycles. Regarding the damage and destruction of the track slab, [PERSON] [31] carried out research on the Shinkansen slab track structure. First, concrete cubes were used as the test piece to carry out a compression fatigue test to determine the required parameters of the fatigue model, and then three-point bending fatigue was performed. In the experiment, a sinusoidal cyclic force was loaded on the prestressed concrete slab. The stiffness change and the evolution of the slab section displacement before and after fatigue were obtained. The initiation process of the track slab cracking failure was also analyzed. [PERSON] and [PERSON] [32] conducted an experimental study on track slab materials taking the freeze-thaw damage and deterioration of track slabs into account. They also considered the sunshine exposure and the chemical reaction of the track slab material. French scholar [PERSON] [33] conducted a structural fatigue experiment on the track slab structure and used sensors to monitor crack development and propagation inside the slab. [PERSON] et al. [34] took into account factors such as concrete strength, reinforcement ratio and steel bar diameter, and used a universal testing machine to stretch the concrete members to simulate the crack development process of the track bed slab in order to test the stress distribution during structural cracking. [PERSON] et al. [35] established a finite element model of a ballastless track with cracks based on the linear elastic fracture theory to analyze the effect of cracks in the base plate under train load. [PERSON] established a finite element model of a heavy-haul train and obtained the mechanical characteristics of track structure under different load conditions [36]. [PERSON] also established the CRTSI ballastless track structure by using the finite element method and studied the displacement and acceleration of the structure under different working conditions [5]. It can be deduced from the foregoing that there are extensive studies on the spatial mechanical characteristics of CRTSIII SBT.