## 4 Model Establishment
### Experimental Validation of the Model
To investigate the impact of the number of dropped layers and dropped spans on the vulnerability of mountain step-terrace frame structures with energy dissipation rocking walls, this study followed the specifications outlined in GB50011-2010 \"Code for Seismic Design of Buildings\" [25]. Various structural configurations were designed, including structures with different numbers of dropped layers and dropped spans. These configurations included a dropped one-story and two-span step-terrace frame structure with energy dissipation rocking walls (C1K2 YBR), a dropped two-story and two-span step-terrace frame structure with energy dissipation rocking walls (C2K2 YBR), and a dropped three-story and two-span step-terrace frame structure with energy dissipation rocking walls (C3K2 YBR) to examine the influence of the number of dropped stories. Similarly, structures with different numbers of dropped spans were designed, including a dropped two-story and one-span step-terrace frame structure with energy dissipation rocking walls (C2K1 YBR), a dropped two-story and two-span step-terrace frame structure with energy dissipation rocking walls (C2K2 YBR), and a dropped two-story and three-span step-terrace frame structure with energy dissipation rocking walls (C2K3 YBR). The Influence of the Number of Dropped Stories and Dropped Spans on the Structural IDA Percentile Curves  
Performing amplitude scaling analysis on seismic waves, IDA curves were plotted in the \(PGA-\theta_{max}\) coordinate system. The 16%, 50%, and 84% percentile curves were obtained through quantile statistical methods. To facilitate the comparison and analysis of the PGA corresponding to the structural exceedance limit states at different percentiles, bar charts of the PGA corresponding to the limit states of structures with different numbers of dropped spans were plotted, as shown in Figure 10, and bar charts of the PGA corresponding to the limit states of structures with different numbers of dropped stories were plotted, as shown in Figure 11.  
From Figures 10 and 11, it can be observed that regardless of the structural limit state, the PGA values corresponding to each percentile line of structures with the same number of dropped stories, but different spans, decreased as the number of dropped spans increased. Figure 10: PGA curves corresponding to the limit state of the quantile curve for structures with different numbers of dropped spans: (**a**) immediate occupancy (IO), (**b**) life safety (LS), and (**c**) collapse prevention (CP). Similarly, the PGA values corresponding to each percentile line of structures with the same number of dropped spans, but different stories, decreased as the number of dropped stories increased. Taking the 84% percentile curve of the IO limit state as an example: for the C2K1 YBR structure, the corresponding PGA value was 0.31038 g, for the C2K2 YBR structure, the corresponding PGA value was 0.29473 g, and for the C2K3 YBR structure, the corresponding PGA value was 0.2537 g. As the number of dropped spans increased, the maximum decrease was 22.34%. For the C1K2 YBR structure, the corresponding PGA value was 0.39339 g, for the C2K2 YBR structure, the corresponding PGA value was 0.29473 g, and for the C3K2 YBR structure, the corresponding PGA value was 0.29473 g. The maximum decrease was 44.59%. Comparing the changes in PGA values of structures with different numbers of dropped stories and dropped spans, it can be seen that the change in the number of dropped stories had a greater impact on the PGA values, corresponding to the percentile curves of the structural limit states, than the change in the number of dropped spans.