# Seismic Comparison of Hybrid Steel-Reinforced Concrete and Conventional Frames
## 2 Considered Buildings and Seismic Analysis  
Simple geometrical 3D models are chosen for investigation here to serve the purpose of this work, which is comparing the seismic performance of hybrid buildings to conventional ones. The selected analysis models have the same geometric configuration, with an identical symmetrical plan across all levels; however, they are made of different structural materials, i.e., reinforced concrete, steel, or a combination of reinforced concrete for the lower part and steel for the upper part. The number of stories is selected from two to six to represent typical small- to medium-rise buildings. Selected 3D models are subjected to strong earthquakes to evaluate their seismic performance by dynamic analysis, which offers more accurate results than other analysis types [47; 48]. The analysis results are evaluated, given the effect of the structural material combined with the most detrimental structural behavior. The findings are numerically justified by story horizontal deformation, story acceleration, and the maximum base shear that is evaluated through dimensionless parameters following current standards [2; 3; 4; 5; 6; 7] and relative research works [49; 50], as explained in the following section. Although various response variables can be found in the literature, in the current investigation, only the selected parameters are preferred so as to maintain the focus of this work on comparative seismic comparisons of the structural response of various 3D models because of the varying material effect. This study excludes asymmetries in planning or loading to avoid additional nonlinearities and focuses on the influence of different structural materials on seismic response. The following section provides a precise description of the model and analysis methods. This investigation considers three series of buildings: a series of conventional r/c 3D frames, one of the traditional steel 3D frames, and a series of hybrid steel-r/c frames. Conventional and hybrid buildings are assigned similar geometrical characteristics and loadings for comparison. The design includes five r/c frames with two to six stories, representing typical reinforced concrete buildings, following the current Eurocode standards [2; 4; 5; 6; 7]. The first story of all r/c frames has a height of 4.0 m, while all upper floors have a 3.0 m elevation (Figure 1). The r/c frame's plan has dimensions of 15.0 \(\times\) 15.0 m\({}^{2}\), comprising three identical 5.0 m spans in both horizontal directions. The choice of material strength depends on the structural demand, ensuring a balance between safety and efficiency. The materials are selected according to standards such as the Eurocodes [2; 3; 4; 5; 6; 7], considering factors like durability, environmental resistance, and cost-effectiveness. The structural material is concrete grade C25/30, which is reinforced with steel B500c, according to Eurocode 2 [2]. At each story, r/c slabs are considered with a 0.15 m thickness, behaving as an inflexible diaphragm, carrying a passive weight of 5.0 kN/m\({}^{2}\) and an active weight of 2.5 kN/m\({}^{2}\)[51]. Following the applicable guidelines [2; 3; 4; 5; 6; 7], the design of the r/c buildings considers typical buildings with an importance factor of 1.0, a zone spectrum acceleration of 0.36 g (where g refers to the gravity acceleration), a ductility class medium (DCM), a viscous damping ratio of 5%, and a design spectrum of I type and ground type C. The analysis assumes minimal impact from deformable ground effects and neglects them, and the maximum behavior factor is considered 3.9 for moment-resisting frames (MRFs), following the applicable code [4; 5; 6; 7]. The seismic loadings on both lateral orientations follow the 0.30 rule of [4; 5; 6; 7], with an accidental eccentricity of 0.05 [4; 5; 6; 7]. The earthquake planning and check of the concrete buildings include the damage restriction for \"brittle non-structural elements\" [4; 5; 6; 7].