## 6 Seismic Performance of the Case Study
### SD Limit State
#### 6.2.2 Nonlinear Static Analysis (Pushover)  
In this study, a nonlinear static pushover analysis was conducted on a comprehensive 3D numerical model of the structure to evaluate its seismic performance under the Significant Damage (SD) limit state. The pushover analysis involved incrementally applying lateral forces to the structure until the target displacement, associated with the SD limit state, was reached. This target displacement was determined by the intersection of the pushover curve with the elastic response spectrum for the specified SD limit state. At this target displacement, the demand values for critical structural elements, including chord rotation and shear demands on beams and columns, were assessed directly within the model. This approach allows for a detailed and accurate evaluation of the structural response under seismic loads by capturing the demands at the exact displacement level required by the SD criteria without resorting to single-degree-of-freedom (SDOF) simplifications. Through this method, the results obtained reflect the behaviour of the entire structure in its three-dimensional configuration, ensuring a more realistic and comprehensive assessment of seismic performance. Figure 19 shows the distribution of capacity-to-demand (C/D) ratios for both rotation and shear in beam and column elements across three floors under maximum demands obtained from pushover analysis. In the case of rotation capacity-to-demand ratios for beams, it was noted that floor 1 carries the highest margins, and a significant number of elements carry high C/D ratios. Floor 2 has noticeably low rotation C/D ratio compared to floor 1, while capacities are still adequate. There is a mixed pattern for floor 3. While several beams still exhibit high rotation C/D ratios, indicating they have adequate capacity, a number of beams approach or drop closer to threshold, indicating these elements have higher rotational demand relative to their capacity. The C/D ratios for shear capacity in the beams are more uniform storey to storey with most beams maintaining C/D ratios well above the threshold. That would tend to indicate the shear demand is not appreciatively increased with height, and in general, the beam elements retain sufficient shear capacity across all the floors. The columns have a different trend in their shear and rotation C/D ratios. In general, high values can be observed for the shear and rotation C/D ratio of floor 1 columns, guaranteeing quite adequate capacity. On the other hand, rotation C/D ratio and shear C/D ratio are very low for floor 2 compared to the values for floor 1, indicating much lower capacity margins. But this trend partly reverses on floor 3, where several columns show higher C/D ratios, especially under rotation. That would imply that the floor 2 columns are really the most vulnerable under both shear and rotational demand, while in floor 3, the margins of capacity are higher, with just a few elements close to the threshold, particularly for rotation. From Figure 16, it can be observed that the inter-storey drift ratios develop a trend consistent with the C/D ratio derived in columns and point to a certain level weakness. The concentration of inter-storey drifts in the second floor brings into focus this level as a soft storey where the displacements concentration is more critical compared with the rest of the floors for seismic loading. This is consistent with the lower C/D ratios for columns of the second floor, as seen in the capacity-to-demand plots. In other words, floor 1 and floor 3 exhibit a balanced ductile and brittle mechanism with higher rotational and shear C/D ratios, indicating strong resistance to both plastic deformations and shear failure. Floor 2, however, shows lower rotational and shear C/D ratios, particularly in columns, suggesting a heightened risk of brittle failure due to limited shear capacity and increased demand under high inter-storey drift.