### Summary
For the region with temperatures exceeding 750 \({}^{\circ}\)C, the cross-section is assumed to lose all bearing capacity. The strengths of steel reinforcement in both the compression and tension zones are determined according to Figure 20, based on the local temperature at their positions. The bearing capacity calculation method for the reduced cross-section is identical to that of the element at a normal temperature. The formula for the normal cross-section bearing capacity of UHPC large eccentric compression specimens in the compression zone under high temperature is as follows:  
When \(x\leq h_{2}\) (the calculation diagram is shown in Figure 21),  
\[N=f_{c}^{T_{2}}b_{2}x+f_{y}^{\prime T}A_{s}^{\prime}-f_{y}^{T}A_{s}-f_{t}^{T_{ 1}}b_{1}h_{1}-f_{t}^{T_{2}}b_{2}(h_{2}-x) \tag{16}\]  
\[ \begin{array}{l}M_{u}=N\Big{(}\eta e_{0}+\frac{1}{2}h-a\Big{)}=f_{c}^{T_{2} }b_{2}x\Big{(}h_{1}-a_{s}+h_{2}-\frac{1}{2}x\Big{)}-f_{t}^{T_{2}}b_{2}(h_{2}-x )\\ \Big{(}h_{1}-a_{s}-\frac{1}{2}x+\frac{1}{2}h_{2}\Big{)}+f_{y}^{\prime T}A_{s}^ {\prime}(h_{0}-a_{s}^{\prime})-f_{t}^{T_{1}}b_{1}h_{1}\Big{[}\frac{1}{2}h_{1} -a_{s}\Big{]}\end{array}  \tag{17}\]  
When \(x>h_{2}\) (the calculation diagram is shown in Figure 22),  
\[N=f_{c}^{T_{2}}b_{2}h_{2}+f_{c}^{T_{1}}b_{1}(x-h_{2})+f_{y}^{\prime T}A_{s}^ {\prime}-f_{y}^{T}A_{s}-f_{t}^{T_{1}}b_{1}(h_{1}+h_{2}-x) \tag{18}\]  
\[ \begin{array}{l}M_{u}=N\Big{(}\eta e_{0}+\frac{1}{2}h-a\Big{)}=f_{c}^{T_{2} }b_{2}h_{2}\Big{(}h_{1}-a_{s}+\frac{1}{2}h_{2}\Big{)}+f_{c}^{T_{1}}b_{1}(x-h_{ 2})\\ \Big{(}h_{1}-a_{s}-\frac{1}{2}x+\frac{1}{2}h_{2}\Big{)}+f_{y}^{\prime T}A_{s}^ {\prime}(h_{0}-a_{s}^{\prime})-f_{t}^{T_{1}}b_{1}(h_{1}+h_{2}-x)\\ \Big{[}\frac{1}{2}(h_{1}+h_{2}-x)-a_{s}\Big{]}\end{array}  \tag{19}\]  
Note: \(N\) is the design value of the axial compressive force; \(f_{c}^{T_{1}}\) and \(f_{c}^{T_{2}}\) are the design values of the axial compressive strength of UHPC at temperatures \(T_{1}\) and \(T_{2}\), respectively; \(f_{t}^{T_{1}}\) and \(f_{t}^{T_{2}}\) are the design values of the axial tensile strength of UHPC at temperatures \(T_{1}\) and \(T_{2}\), respectively; \(f_{y}^{\prime T}\) is the design values of the compressive strength of ordinary steel bars at the corresponding temperatures; \(f_{y}^{T}\) is the design value of the tensile strength of ordinary steel bars at the corresponding temperature; \(A_{s}\) and \(A_{s}^{\prime}\) are the cross-sectional areas of the longitudinal ordinary steel bars in the tension zone and the compression zone,  
Figure 20: The yield strength of steel bars at high temperature. respectively; \(b_{1}\) and \(b_{2}\) are the widths of the rectangular cross-section; \(h_{0}\) is the effective height of the cross-section; \(h_{1}\) and \(h_{2}\) are the heights of the rectangular cross-section; \(x\) is the height of the equivalent compression zone; \(a_{s}\) is the distance from the resultant force point of the longitudinal ordinary steel bars in the tension zone to the tension edge of the cross-section; \(a_{s}^{\prime}\) is the distance from the resultant force point of the longitudinal ordinary steel bars in the compression zone to the compression edge of the cross-section; and \(\eta\) is the eccentricity magnification factor of the axial compressive force considering the influence of the second-order moment for the eccentrically compressed specimen. In this section, the accuracy of the proposed calculation method is verified through finite element analysis. The numerical model Q-1 is established, with the following specifications for the UHPC wall:  
The wall dimensions are 800 mm (width) \(\times\) 400 mm (thickness) \(\times\) 2000 mm (height), with an eccentricity of 0.5. The reinforcement ratio is 1%, corresponding to double-layer reinforcement, while the steel fiber content is 0%. The specified concrete strength is 100 MPa. For longitudinal distributed reinforcement, each layer consists of eight 16 mm diameter HRB 400-grade steel bars spaced at 100 mm intervals.