## 4 Results
### Linear Analysis: Lateral Force Method and Response Spectrum Method  
A preliminary analysis was conducted for seismic loading calculated in the original seismic design, using the lateral force method and accounting for the assumptions on the building importance and seismic zone. Lateral forces act only on the building part above ground level. This assumption was verified later by detailed seismic analyses. Moreover, the linear distribution of forces along the height was assumed, which was shown to be a governing load pattern in the nonlinear pushover analyses performed after. It can be stated that the seismic base shear force of the building, according to the original seismic design, is approximately equivalent to the shear force according to Eurocode 8, with a\({}_{\rm g}\) = 0.15 g.  
The cracking of structural elements was accounted for, as it was assumed that the structure will reach a significantly damaged state. Only story shears are presented in the following figure (Figure 14), because this analysis method is only a referent point for the more complex analyses. Ratios of the base shear to vertical loading and average story shear stresses were calculated for the critical stories three (ground floor) and five (third story above ground level). Base shear ratios in story three amount to 12% for the X and Y directions, while in story five these values are 18.7% for the X and Y directions. It may be observed that the base shear ratios are larger for story five (third story above ground level) than for story three (ground floor), and that the average shear stresses in the Y direction are higher than in the X direction, due to the lower total wall area. The average shear stress amounts to 0.48 and 0.73 MPa for directions X and Y at story five, while at story three these stresses are 0.32 and 0.37 MPa for directions X and Y. It should be emphasized that the average shear stress in a story may only be used for the preliminary assessment of the stress level in walls, because the building plan is very irregular and the walls are not uniformly distributed. A moderate level of compression stresses in the walls at stories three and five is favorable and increases the allowable stress levels. However, due to plan irregularity and the very uneven distribution of walls, tension stresses in walls may occur along the edge. Figure 13: Three-dimensional view of mode shapes of the initial numerical model: (**a**) first; (**b**) second; (**c**) third. Response spectrum analysis was conducted in accordance with valid seismic regulation, using the design response spectra for the 95 and 475 year return periods. The importance factor was not accounted for, although for a building of such importance the value of 1.4 should have been used. This decision was made in order to enable a comparison of the structural response to earthquake loading defined within different analysis methods. Generally, an importance factor is used to analyze buildings for earthquakes of a larger return period. All other assumptions were accounted according to Eurocode 8. An eccentricity of 5% was taken into account and the behavior factor was defined as 1.5, because of primary non-ductile failure mechanisms and a lack of transversal reinforcement. The cracked state of the cross-sections was taken into account, as it may be assumed that the structure will reach a state of significant damage. The story shears for the design response spectra for 475 years return periods are presented in Figure 15.  
Figure 14: Story shears for the lateral force method applied in the X and Y directions. Figure 15: Story shears in directions X and Y for the design response spectrum case (return period (RP) 475 years). Ratios of the required to as-built reinforcement in critical structural elements at stories three and five are presented in Figure 16, so critical locations may be identified. As previously mentioned, minimal reinforcements in elements according to the valid code differs from the original code, so particular elements do not comply with modern regulations.