## 5 Determination of the Seismic Response of the Case Studied
### Nonlinear Static Analysis  
Nonlinear static analysis (pushover) has been applied to the model considering the distribution of lateral loads corresponding to the distribution of the first mode of vibration [38], although it is evident that the structural axis with masonry infill panels (axis D) has a stiffness greater than that of a structural axis without masonry infill panels (axes A, B, and C) (Figure 4). In this way, the effect of the irregularity in the stiffness distribution on the torsional behavior of the structure can be captured. The nonlinear static analysis is carried out in both the conventional and adaptive modes, since the validity of the first type of analysis is limited by the irregular nature of the structure, conferred by the presence of unevenly distributed masonry infill panels. The advantage of adaptive nonlinear static analysis is that it allows the variations in the lateral stiffness of the model to be captured when it undergoes alterations in its elements. The capacity curves of the conventional nonlinear static analysis are shown in Figure 8, in which the curves corresponding to the X direction of analysis change in both the positive and negative directions (see Figure 8a,b, respectively). The capacity curves show the evolution of the normalized basal shear with respect to the seismic weight vs. the normalized ceiling displacement with respect to the total height of the building (global drift). Additionally, note that the nonlinear analysis is carried out in only the X direction since the Y direction is similar in both the geometric and mechanical characteristics adopted. These curves show how the failure of the masonry infill panels affects the overall response of the structure (for a global drift close to 0.8%); however, this failure is not well defined in the curves obtained from the conventional analysis. On the other hand, the capacity curves obtained when applying adaptive pushover analysis, which are presented as variants of the vector of lateral forces applied to the structure by virtue of the changes that take place in the modal shapes as different levels of element damage occur as the simulation progresses, are interesting. The capacity curves in Figure 9a,b are shown with the idealized curves, which are determined using the method proposed in [39; 40]. With the ultimate displacement and the yield displacement of the idealized curve, the ductility (\(\mu\)) of the model is determined according to Equation (1) with the ultimate displacement (\(\Delta_{u}\)) and the yield displacement (\(\Delta_{y}\)), and is summarized in Table 5. Note that, although the results of the ductility calculated with the conventional and adaptive curves are quite similar, the adaptive nonlinear static analysis has allowed  
Figure 8: Resulting capacity and idealized curves obtained from conventional pushover: (**a**) lateral forces (+) and (**b**) lateral forces (\(-\)). the curves for which the global drift resulted in the failure of the masonry infill panels to be clearly identified. \[\mu=\frac{\Delta_{u}}{\Delta_{y}} \tag{1}\]  
Another of the characteristics of the response that is interesting to evaluate is the variation in the rotations with respect to the displacements at the center of gravity of the roof level during the pushover analysis. Figure 10a,b show the results of the rotations at the centers of gravity \((CG)\) of each floor for both the conventional and adaptive incremental pushover analyses. Beyond the similarity of these curves, it can be seen that, at the beginning of the analysis, there is a linear increase in the rotations of the centers of gravity of each floor, but once a global drift of 0.8% is reached, there is a significant reduction in these rotations. However, residual rotations remain that cannot be recovered due to the displacement caused by the collapse of the building; thus, the failure mechanism clearly includes significant rotations in levels 3 and 4 of the building.