## 2 3D FEM Model
### Subsoil Model  
Three variants of the subsoil model allowing various properties of the subsoil to be taken into account were considered. The first variant of the subsoil model, marked as SM1, assumed nonflexible subsoil (foundations of the building are fixed in the soil with infinite stiffness). In the second one, noted as SM2, the flexibility of the subsoil was represented through the use of spring elements that allow for movement in both vertical \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Structural Element** & **Material** & **Elastic Modulus [GPa]** & **Density [kg/m3]** & **Poisson’s Ratio [–]** \\ \hline strip footing & concrete & 20.8 & 2500 & 0.25 \\ \hline foundation tie rods & reinforced concrete & 19.7 & 2500 & 0.25 \\ \hline foundation walls & reinforced concrete & 23.1 & 2500 & 0.25 \\ \hline ceilings & reinforced concrete & 27.0 & 2500 & 0.25 \\ \hline ceiling ties & reinforced concrete & 27.0 & 2500 & 0.25 \\ \hline  & brick & 2.85 & 1800 & 0.25 \\ \cline{2-5} load-bearing walls & reinforced concrete & 31.0 & 2500 & 0.25 \\ \cline{2-5}  & cellular concrete & 1.80 & 600 & 0.25 \\ \hline partition walls & brick & 2.85 & 1800 & 0.25 \\ \hline lintels & reinforced concrete & 27.0 & 2500 & 0.25 \\ \hline stairs & reinforced concrete & 27.0 & 2500 & 0.25 \\ \hline supporting knee walls & brick & 2.85 & 1800 & 0.25 \\ \hline prefabricated roof panels & reinforced concrete & 27.0 & 2500 & 0.25 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Material parameters of structural building elements. and horizontal planes. In the third variant of the subsoil model, marked as SM3, damping was incorporated into springs to account for energy dissipation. The SM2 subsoil model, using elastic springs, allows for the consideration of the soil's capacity to deform elastically under seismic-type loads. Therefore, the COMBIN14 element from the ANSYS element library was utilized to achieve this modeling. The springs were aligned along the horizontal x- and y-axes and the vertical z-axis, reflecting the soil's capacity to deform elastically under seismic loads. The COMBIN14 spring elements in ANSYS were adept at representing the three-dimensional interaction between the soil and the structure. Figure 6 illustrates the implementation of a spring-based soil model (SM2) within the ANSYS simulation environment and shows the transverse, longitudinal, and vertical placement of spring elements that emulate the soil's resistance. The stiffness values for the spring elements that facilitate both horizontal (in transverse and longitudinal directions) and vertical movement were determined by employing the Savinov soil model and the soil reaction coefficient Cz, which is determined by the ratio of the vertical unit base pressure to the elastic strain [27]. The Savinov method for determining the dynamic elastic properties of the subsoil is applicable to rectangular foundations. It is assumed in the Savinov method that the subsoil is an unlimited elastic plane on which a homogeneous membrane is placed and stretched in all directions (there are no friction forces between the plane and the membrane). The values of the Cz coefficient depend on the geotechnical category of the soil. The spring stiffness along all directions was parametrically varied, reflecting diverse soil conditions as characterized by the modulus coefficient Cz, with evaluations conducted across a wide stiffness range from 35 MPa to 65 MPa. The third variant of the subsoil model (SM3), in addition to soil flexibility, also took damping into account. Damping coefficients were calculated, considering the soil density equal to 1800 kg/m\({}^{3}\) (for medium-dense sands), the shear wave velocity (200 m/s), and the total contact area of the foundation. This information was collated from geotechnical surveys and corroborated by peer-reviewed literature on regional seismicity. Numerical analysis of the transmission of the free-field wave to the building foundation was based on the Newmark algorithm with Rayleigh damping model [28] and a damping ratio equal to 5%.