# Seismic Comparison of Hybrid Steel-Reinforced Concrete and Conventional Frames
## 2 Considered Buildings and Seismic Analysis
The dimensioning of the hybrid models is completed individually for the steel and concrete portions, with maximum values of 4.0 and 3.9, which are appropriate [4; 5; 6; 7] for the usual rigid soil assumption [4; 5; 6; 7]. Composite slabs of a 0.15 m thickness act as an inflexible diaphragm at each story of the hybrid models. Table 3 provides the final dimensioned sections of the vertical and horizontal structural members of the hybrid structures. Comparing Tables 1 and 3, the reinforced concrete columns of the hybrid models tend to have slightly smaller cross-section dimensions than the concrete buildings. The steel columns and beams of the hybrid frames have smaller sections than the ones, respectively, for the steel frames (Tables 2 and 3). The interaction between steel and concrete components is crucial in defining their overall structural behavior in hybrid structures. Two extreme boundary conditions are incorporated to account for this interaction, complying with the findings of Refs. [1; 25; 26; 27; 28; 40]. The \"fixed support\" condition of the steel columns represents a fully restrained connection, enabling complete moment transfer in both horizontal directions. In contrast, the \"fixed-pinned\" connection ensures stability by allowing fixation along the minor sectional axis while permitting a pinned connection along the primary sectional axis [25; 26; 27; 28]. Table 3 provides the detailed specifications and modeling considerations for the boundary conditions of the hybrid models for examination. SAP2000 software [52] performs modal analysis on the three series of investigated models--r/c, steel, and hybrid. Table 4 presents the main modal characteristics of the 15 models, listing the \"modal period\" and \"participating mass ratios\" [53] for each model's  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multicolumn{2}{c}{**Hybrid Building (Figure 3a)**} & & & & **Beams** & \\ \cline{3-6} \multirow{2}{*}{**Story**} & \multirow{2}{*}{**Material**} & \multicolumn{2}{c}{**Columns**} & & **Beams** & \\ \cline{3-6}  & & **Section (m2)** & **Axial bars** & **Stirrups** & **Section (m2)** & **Axial Bars** & **Stirrups** \\ \hline
1 & Reinforced concrete & 0.50 \(\times\) 0.50 & 802 22 & \(\mathcal{O}\) 8/10 & 0.25 \(\times\) 0.60 & 80\(\mathcal{O}\) 18 & \(\mathcal{O}\) 8/10 \\ \hline
2 & Structural steel & \multicolumn{2}{c}{HEA360} & & & \multicolumn{2}{c}{IPE270} \\ \hline \multicolumn{2}{c}{**Hybrid Building (Figure 3b)**} & & & & & \\ \hline \multirow{2}{*}{**Story**} & \multirow{2}{*}{**Material**} & \multicolumn{2}{c}{**Columns**} & & **Beams** & \\ \cline{3-6}  & & **Section (m2)** & **Axial bars** & **Stirrups** & **Section (m2)** & **Axial Bars** & **Stirrups** \\ \hline
1 & Reinforced concrete & 0.55 \(\times\) 0.55 & 16020 & \(\mathcal{O}\) 8/10 & 0.25 \(\times\) 0.60 & 80\(\mathcal{O}\)20, 80\(\mathcal{O}\)10 & \(\mathcal{O}\) 8/10 \\ \hline
2 & Reinforced concrete & 0.50 \(\times\) 0.50 & 8020,80\(\mathcal{O}\)10 & \(\mathcal{O}\) 8/10 & 0.25 \(\times\) 0.60 & 80\(\mathcal{O}\)1 three primary modes. The modal periods of the steel buildings are more significant than the corresponding values for the r/c and hybrid ones (Table 4). In the hybrid modes, the modal periods have relatively close values for the two extreme supports--\" fixed\" and \"fixed-pinned\"--with slightly greater values observed for the \"fixed-pinned\" case compared to the \"fixed\" one (Table 4). Regarding the three-, four-, and five-story models, the hybrid models present intermediate values of the modal periods compared to the corresponding values for the concrete and steel ones. The one- and six-story hybrid models present smaller values of the modal periods than the conventional models, as observed in Table 4.  
Intense near-fault seismic events are chosen as inputs at the \"nonlinear time history (NLTH)\" [25] assessment of the conventional and the hybrid models by using SAP2000 software [52].