## 5 Conclusions  
This study established a finite element model for the base-isolated structure of a nuclear power plant's diesel building and validated the modeling methodology's effectiveness through shake table test results. To address the overturning issue observed in the tests, a hybrid base-isolation scheme was proposed, and a corresponding finite element model was developed. IDA was employed to conduct seismic fragility analyses on both the base-isolated and hybrid base-isolated structural models. The following conclusions were drawn:  
1. The IDA curves using shear strain (\(\gamma\)) as the damage measure exhibit a reduction in slope near the seismic intensity corresponding to isolator yielding. In contrast, IDA curves using the TP value as the damage metric show an inflection point near the seismic intensity corresponding to isolator tension and reduced vertical stiffness. Under identical earthquake records, the slope of the IDA curves for hybrid base-isolated structures is steeper than that for conventional base-isolated structures, indicating that the isolators are less prone to damage. Additionally, at the same seismic intensity, the damage measure values for hybrid base-isolated structures are smaller, reducing the likelihood of overturning under seismic loads and improving overall seismic performance. 2. Under the same limit state, the fragility curves for hybrid base-isolated structures are flatter compared with those for conventional base-isolated structures. This indicates that hybrid base-isolated structures have a lower probability of failure at a given limit state, demonstrating superior anti-overturning performance. 3. Based on a statistical analysis of fragility curve data, hybrid base-isolated structures exhibit lower fragility and greater collapse resistance reserves compared with conventional base-isolated structures. This is reflected in both the fragility matrices and the CMR. 4. Using the TP value as the damage metric for seismic fragility assessment yields more conservative results. Therefore, in structural design, particular attention should be paid to enhancing the tensile capacity of isolators to mitigate potential damage. 5. The fragility assessment based on shear strain (\(\gamma\)) provides valuable references for determining collision trench limits in seismic isolation systems for nuclear power plant diesel buildings. 6. The collaborative design of isolation for non-structural components will be regarded as the next research direction in the future. By using dynamic characteristics such as floor response spectra obtained from the shaking table test, the dynamic coupling effect between the isolation layer and non-structural components such as building equipment (diesel generators) and pipelines will be optimized to avoid chain failure caused by local damage. Moreover, uncertainty analysis and seismic fragility assessment will be conducted for the failure modes of non-structural components. \begin{table}
\begin{tabular}{c c c} \hline
**Structure** & **Shear Strain (\(\gamma\))** & **TP** \\ \hline Isolated structure & 1.88 & 1.52 \\ Hybrid isolation structure & 2.30 & 1.79 \\ \hline \end{tabular}
\end{table} 
Table 9: Anti collapse reserve coefficient based on shear strain \(\gamma\) and TP values as damage measures. **Author Contributions:** Conceptualization, Y.X. and X.G. ; methodology, Y.X. and X.G. ; software, Y.X., X.G. and K.X. ; data curation, Y.X., X.G., K.X. and J.Z. ; writing--original draft preparation, Y.X. ; writing--review and editing, X.G. ; visualization, Y.X. ; project administration, X.G. ; funding acquisition, X.G. All authors have read and agreed to the published version of the manuscript. **Funding:** This research study was funded by the science and technology project of Beijing University of Technology (No. 40004012201909). **Institutional Review Board Statement:** Not applicable. **Data Availability Statement:** The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.