## 5 Global Structural Response of the Case Study
Figures 14 and 15 illustrate the Torsional Drift Ratio (TDR) for each side of the building (i.e., top, right, bottom, and left side of the building) across the considered limit states in both the X and Y directions. The TDR plot for floors 1, 2, and 3 developed for different loading orientations gives insight into the torsional behaviour of each floor when seismic forces are applied. It shows that the response of the structure will be different at different levels, especially for the case of an asymmetric distribution of building mass. Regarding floor 1, higher TDR values are observed along the \"left\" side--up to 75% under the XY component and along the \"top\" side--up to 64.3% for the DL limit state under the YX component--strong torsional deformation with significant negative TDRs set on the \"bottom\" and \"right\" sides, respectively--that is, a sign of displacement inwards of these two sides. With such evident torsional sensitivity, greater attention is brought specifically to reinforcement in high-TDR areas, like adding shear walls or braces to improve stability laterally. Floor 2 has a better profile of Torsional Drift Ratio, hence it is almost in the middle: for instance, a value of 29.8% in the 'Top' side for loading in the XY direction for the DL limit state and a minimal negative TDR. It can easily be justified by taking into consideration that floor 2 is near the center of mass of the building and thus is somewhat a stable point  
Figure 14: Torsional Drift Ratios for Floors 1, 2, and 3 under XY and YX seismic load orientations, illustrating variations in torsional response across building sides in the DL limit state. within the building. Therefore, any reinforcement of this floor could increase the structural stability throughout the entire building. Furthermore, the low sensitivity of floor 2 to changes in direction drew greater attention to the symmetry of mass and stiffness as a countermeasure against torsion. In contrast, the top floor delivers lower TDR values and reaches a maximum of 24.3% for the DL limit state on the 'Top' side for XY loading, while negative values remained minor. The reduced torsional response agrees with expectations for the upper floors, where a reduced mass, shorter moment arm and therefore lower torsional vulnerability is present. Again, this supports the design approach of minimising mass on upper floors in order to bound the effects of torsion and to provide greater stability to the overall structure. The implications of TDR analysis are practical in seismic design. High-TDR floors such as floor 1 benefit from reinforcement targeted at particular sides that experience high torsional drift. The low TDR values of floors 1 and 2 are indicative of the advantage of symmetric distribution of mass and stiffness in reducing torsional response. Floor 3's minimal TDR suggests that decreasing mass or stiffness in upper floors can further limit torsional effects, contributing to overall building stability. Comparing TDR values under Damage Limitation (DL) and Severe Damage (SD) limit states reveals that the TDR is more pronounced in the DL state, where initial structural flexibility permits greater lateral deformation. Whereas, in the SD state, the TDR values are mostly lower, reflecting the reduced response of the structure once its ultimate capacity has been reached. From these comparisons, it is clear how important the assessment of both the serviceability and the ultimate performance is in respect to comprehensive seismic resilience.