# Evaluation of Structural Stresses of Mountain-Embedded Railway Systems
## 4 Analytical Investigation of the Behavioral Characteristics of the Mountain-ERS Track System  
### Structural Safety Evaluation of the Mountain-ERS under Factored Service Loading Conditions  
As discussed previously, the safety of the mountain-ERS track system was also evaluated. The maximum principal stress of each concrete element and the von Mises stresses of the reinforcing bars were investigated, as shown in Figures 17 and 18, respectively. The estimates of the maximum principal tensile stress of each concrete component were obtained as follows: 3.910 MPa in the middle section of the concrete panel at the position where the rack rail was installed, 0.404 MPa in the bedding layer, and 0.425 MPa in the subgrade layer. Figure 17: Principal stress contours and locations of the maximum principal tensile stress of concrete elements (reference model): (**a**) precast concrete panel, (**b**) bedding layer, and (**c**) subgrade layer. The maximum principal stress of the concrete elements did not exceed the tensile strength of the concrete, except at the surface, where discrete longitudinal forces were applied to the precast concrete panel. This was because of the postulated assumption for the conservative safety assessment of mountain-ERS, which considered the starting and braking loads of the mountain train. In addition, the differences between the values of the maximum principal tensile stress (3.910 MPa) and tensile strength of the concrete panel (3.81 MPa) were negligible. In the case of the starting and braking loads of the mountain train, an arbitrarily applied value of the prototype train was applied in this research; therefore, it is necessary to evaluate safety and calculate and apply the exact values based on additional future research. For the reinforcing bars, a von Mises stress of 36.93 MPa was generated at the position where the longitudinal loads on the rack rail were installed, which was lower than the yield strength of the reinforcing bars (400 MPa). Feasibility Study of High-Strength Concrete Material for Enhancing the Structural Safety of the Mountain-ERS Track  
In the ERS track, both train and wind loads were transmitted from the rails to the precast concrete panels. Longitudinal loads, such as braking forces, were transmitted from a rack rail to a precast concrete panel. Precast concrete panels must possess sufficient strength to withstand such loads. The bedding and subgrade layers transferred the loads transmitted from the precast concrete panels to the underlying ground. To analyze the effect of the strength of the precast concrete panel and the behavior of the mountain-ERS track under these conditions, parametric case studies were conducted by changing the material properties of the precast concrete panel. Linear analyses were conducted, and the elastic modulus of the concrete was adjusted with respect to its compressive strength. The compressive strengths of the precast concrete panel were assumed to be 45 MPa (35,684 GPa, reference model), 60 MPa (38,776 GPa), 75 MPa (41,440 GPa), and 100 MPa (45,241 GPa), and the corresponding elastic moduli were considered based on Equation (1) ([12]) (the values in parentheses indicate the modulus of elasticity of concrete). The results are presented in Figure 19.  
Figure 18: Von Mises stress contours and location of the maximum stress value of reinforcing bars inside the precast concrete panel (the reference model). When a high-strength concrete material was applied to the precast concrete panels, the tendency of S22 to occur along the sections was similar. However, for S11 and S33, the stress tended to increase at the bottom of the panel when high-strength concrete was used. These tendencies were attributed to the difference in the elastic modulus of the precast concrete panel from those of the reinforcing bars, bedding layer, and subgrade layer.