# Seismic Comparison of Hybrid Steel-Reinforced Concrete and Conventional Frames
## 1 Introduction
[29] created an innovative, simplified algorithm for estimating the lateral loads for mixed structures. [PERSON] and [PERSON] suggested using an algorithm approach for the optimal design of mixed structures with given cost terms [30]. [PERSON] et al. [31] proposed seismic factors for mixed \"concrete/steel buildings\". A \"damage detection\" procedure in plane \"mixed frames\" was performed using a \"wavelet analysis\" by [PERSON] et al. [32]. From the previously mentioned research studies, an interest arises in investigating selected cases of the hybrid building form. However, a systematic comparison of hybrid steel-r/c structures to typical r/c or steel structures has not yet been performed. Hybrid structures comprise two different structural materials in height-wise story distribution, where the current code [4; 5; 6; 7] does not supply a value-damping ratio, which is necessary for structural analysis, leaving a research gap. [PERSON] [33] suggested the modal-damping ratio values for plane mixed steel-r/c building frames. [PERSON] [34] provided diagrams for the estimation of an \"equivalent\" damping ratio for mixed \"building systems\". [PERSON] et al. [35; 36] supplied a math technique for the calculation of a single \"damping ratio\" for \"mixed buildings\", which was verified by [PERSON] et al. [37] and successfully applied in recent research studies [1, 25; 26; 27; 28]. [PERSON] et al. [38; 39] investigated the application of rate-independent damping devices in tall base-isolated buildings. The previously mentioned research works refer to structures resting on an ideal rigid soil assumption [4; 5; 6; 7], as usually considered for typical buildings. In addition, [PERSON] [40] assessed the contribution of ground deformability on the hybrid frames' demeanor as opposed to the inflexible soil by checking the effect of a variable excitation angle as raising interest in various works [41; 42; 43]. [PERSON] et al. [45] and [PERSON] and [PERSON] [46] investigated the effect of earthquake orientation. Apart from the mentioned research works, a scientific gap is obvious in examining the dynamic nonlinear response of hybrid structures. Thus far, previous studies have not addressed the comparison between ordinary reinforced concrete or steel buildings and hybrid steel-r/c structures, even for the usual rigid soil assumption. This study fills this gap by focusing on this novel investigation. Specifically, it presents the first systematic examination of the seismic nonlinear behavior of hybrid symmetric 3D models compared to conventional ones, considering the effects of varying near-fault excitation angles. This study employs practical, simplified 3D models with symmetrical plans designed according to the current codes for conventional RC and steel structures while using reasonable approximations for hybrid forms. This approach ensures that the findings broadly apply to various buildings. This study identifies the most critical response patterns through dynamic earthquake analyses of the selected models, emphasizing the importance of comparing hybrid structures to traditional ones. The necessity of this seismic comparison is further elaborated in the following sections.