## 4 Analysis of the Test Results
### Relative Displacement between the Track System Layers  
#### 4.2.1 Vertical Relative Displacement between Layers  
According to the LVDT displacement sensor setup in Figure 5, the relative displacement is considered positive when the upper structure layer moves vertically upward relative to the lower structure layer and negative in the reverse case. Figure 8a shows the vertical relative displacement between the track bed and the simply supported beam at different times during the high-temperature cycle in summer. It can be seen from the figure that, due to the relatively high temperature of the structure at 19:00 (10 h after the initial condition was recorded), the vertical relative displacement between the track bed and the beam body reaches a maximum value. The vertical relative displacement between the base plate and the simply supported beam is larger at the 1/4 L and 3/4 L sections, while that at the mid-span is insignificant. Due to the relatively low temperature of the structure at 7:00, the vertical relative displacement between the layers reaches a minimum. The displacement trend between the track bed and the simply supported beam is the same as that at 19:00 at the different sections. The curve of the vertical relative displacement between the track bed and the simply supported beam at the two different times (19:00 and 7:00) forms the upper and lower envelope for the vertical relative displacement. The fixed end at 0 L is set with shear slots, so the vertical relative displacement between the track system and the beam body is greatly restricted, and the vertical displacement of the two floors is essentially zero for the daily temperature load. Because the vertical relative displacement between the base plate and the beam body at section 0 L of the test beam is restricted, the vertical deformation and displacement of the track system are transmitted along the longitudinal direction of the beam body. The trend of the interaction between the layers of the structure is reflected in the position with relatively small constraints nearby, so the base plate and the beam body at section 1/4 L near the shear slot side are away from each other, and the vertical relative displacement between the layers is the largest at approximately 0.3 mm, which is far greater than the displacement value at 3/4 L.  
The vertical relative displacement between the base plate and the beam at section 1/4 L is the largest compared to that of the other sections, and the vertical relative displacement time history curve at this position is shown in Figure 8b. Due to the thermal insulation of the rail system and the hysteresis of temperature changes, the temperature of the base plate and the beam body is the highest and relatively stable during the period from 17:00 to 2:00 the next day, the relative displacement value of the two structural layers is the largest and remains unchanged, about 0.3 mm; at 7:00 the next day, the vertical relative displacement value between the base plate and the beam body is the  
Figure 8: Vertical relative displacement between the base plate and beam body. (**a**) Vertical relative displacement; (**b**) vertical relative displacement time history curve at 1/4 L.  
smallest and returns to the initial state; the next day, with the temperature rising, the vertical relative displacement value of the inner layer is the smallest. The vertical relative displacement increases gradually. The displacement and deformation of the structure will cause the change of the bearing state of the ballastless track, showing a non-uniform support state, causing the change of the stress and transmission mode of the track structure, and increasing the local stress and deformation. Since the peak value of the vertical relative displacement at this position is far greater than that at other positions, maintenance personnel should pay attention to this position of track system during service in hot summer, and strengthen daily inspection and disease prevention measures.