### Summary  
In this chapter, a UHPC wall model is established to investigate the bearing capacity of specimens under varying temperatures, reinforcement ratios, steel fiber volume fractions, and concrete strength grades, providing a theoretical foundation for the design of UHPC wall structures in new nuclear power plants. The main conclusions of this chapter are summarized as follows:  
1. Load eccentricity is a dominant factor influencing the ultimate load of UHPC walls. Under identical parameters, the ultimate load of elements decreases with increasing eccentricity, while the attenuation rate of ultimate load with temperature slows down. 2. Increasing the reinforcement ratio or steel fiber volume fraction significantly enhances the bearing capacity of UHPC walls and mitigates the high-temperature attenuation of ultimate load. 3. Elevating the UHPC strength grade accelerates the high-temperature attenuation of ultimate load. Calculation Formula for the Bearing Capacity of UHPC Eccentrically Compressed Specimens Under High Temperature  
Under high-temperature conditions, the failure mechanism of small eccentric compression elements involves complex calculations, making it infeasible to derive a unified formula analogous to that for large eccentric compression elements. Therefore, this section focuses on investigating the calculation method for the normal section bearing capacity of rectangular cross-section UHPC large eccentric compression specimens under high-temperature conditions. The equivalent cross-section method is adopted herein to address the effects of high temperature on the bearing capacity of UHPC members [37]. Through experimental research and theoretical analysis, [PERSON] et al. [32] revealed that the failure mode and cross-sectional stress-strain behavior of reinforced concrete eccentric compression elements under high temperature exhibit similarities to those at normal temperature, with the exception that the strengths of steel bars and concrete must be reduced correspondingly according to temperature. Based on this theory, the following assumptions are made in this section:  
1. Plane-section assumption: the cross-section remains plane and perpendicular to the longitudinal axis before and after deformation. 2. Negligible bond-slip: the interaction between steel reinforcement and UHPC is assumed to be perfect, without considering bond-slip effects. 3. Known temperature field: the temperature distribution across the entire cross-section of the specimen is assumed to be known and uniform. 4. Bilinear model for UHPC strength: The compressive strength of UHPC under high temperature (see Formulas (1) and (2)) and tensile strength (see Formulas (3) and (4)) are simplified using a two-step bilinear model. 5. Piecewise-linear and curved model for steel strength: The yield strength of steel reinforcement under high temperature (see Formula (8)) is modeled as a combination of linear segments and a curve. The simplified model of the compressive strength of UHPC under high temperature is shown in Figure 18, and the simplified model of the tensile strength of UHPC under high temperature is shown in Figure 19.  
The yield strength model of the steel bars under high temperature is shown in Figure 20.  
Figure 19: Simplification of the tensile strength of UHPC at high temperature. Figure 18: Simplification of the compressive strength of UHPC at high temperature. Based on the above assumptions, the reduced homogeneous cross-section of the UHPC specimen under high temperature can be derived. The cross-sectional reduction criterion is defined by identifying the 300 \({}^{\circ}\)C and 750 \({}^{\circ}\)C isotherms on the cross-section, as follows:  
1. For the region with temperatures between 0 and 300 \({}^{\circ}\)C, the full cross-sectional area is retained. 2. For the region with temperatures between 300 and 750 \({}^{\circ}\)C, the cross-sectional width is halved, retaining half of the original cross-sectional area. 3.