### Summary
Similarly, the horizontal distributed reinforcement in each layer includes eleven 22 mm diameter HRB 400-grade bars spaced at 190 mm. The model Q-1 is subjected to one-sided fire exposure on the compression face, following the ISO 834 standard fire curve. The concrete heat transfer coefficient settings remain consistent with the previous description. To simulate varying temperature conditions, the following loading protocol was adopted: the ISO 834 standard fire curve was applied with heating durations of 4000 s, 8000 s, and 12,000 s, corresponding to distinct thermal states. Figure 23 illustrates the cross-sectional temperature distribution of the UHPC wall (Model Q-1) under these three heating durations. The results demonstrate that the temperature decreases progressively with increasing cross-sectional height, consistent with one-sided fire exposure. Heat transfers from the heated surface to the opposite side, creating a pronounced temperature gradient. Furthermore, the heating duration significantly affects the temperature distribution. Longer heating times result in higher temperatures at  
Figure 21: Calculation diagram of bearing capacity when \(x\leq h_{2}\). Figure 22: Calculation diagram of bearing capacity when \(x>h_{2}\). the same cross-sectional height, reflecting cumulative heat absorption and gradual inward thermal penetration. As illustrated in Figure 24, a comparison is made between the theoretical values calculated using the proposed formula and the finite element simulation results. Both curves exhibit a consistent downward trend with increasing heating duration, demonstrating the progressive deterioration of the structural bearing capacity under prolonged thermal exposure. This behavior can be attributed to the thermal degradation of material properties: both the compressive strength of UHPC and the mechanical performance of steel reinforcement deteriorate at elevated temperatures, ultimately reducing the member's load-bearing capacity. Further observation of the relationship between the simulated and calculated values reveals that their changing trends are generally consistent. This indicates that the calculation method can reasonably reflect the variation pattern of the bearing capacity with heating time, demonstrating its theoretical rationality. However, at each time point, the simulated values are slightly lower than the calculated values. This difference may arise from the following reasons: simplifying assumptions adopted in the calculation process, such as using averaged material parameters or idealized models, whereas the simulation better approximates real conditions by accounting for more complex influencing factors. The numerical results demonstrate that at a heating duration of 4000 s, the theoretical calculation yields a bearing capacity approaching 4000 kN, while the finite element analysis produces a marginally conservative estimate. This trend persists at 12,000 s, where the calculated capacity of approximately 2500 kN again exceeds the simulated value by a small but consistent margin. Such systematic underestimation in the simulation results requires  
Figure 23: Cross-sectional temperature distribution. Figure 24: Comparison between the simulated and calculated values of bearing capacity. careful consideration in structural design applications, as the analytical method appears to provide slightly non-conservative capacity predictions. These findings collectively indicate that while the proposed computational model successfully captures the essential degradation trend of structural capacity with prolonged heating, discernible discrepancies remain. Future investigations should prioritize model refinement through the integration of additional realistic parameters, including material heterogeneity and non-uniform thermal distributions, to enhance predictive accuracy for practical engineering implementation.