Comparative Seismic Performance of Symmetrical Mixed RC–Steel and Reinforced Concrete Buildings

Reinforced concrete (RC) buildings are among the most common structural systems in seismic regions, and current design codes provide well-established provisions for their analysis and detailing under strong earthquake loading. However, in practical applications, mixed structural configurations are frequently used, in which an RC substructure supports an upper steel superstructure (SS) of similar geometry. Despite their widespread use, mixed RC–steel systems are not explicitly addressed in existing seismic design codes, highlighting the need for further investigation.

In this study, the seismic performance of mixed RC–SS in-plan symmetrical systems is evaluated through nonlinear time-history analyses using a set of strong earthquake records. For comparison purposes, geometrically similar RC frames with symmetric layouts are also examined in the 3D space under the same excitations. The numerical models incorporate material nonlinearity to realistically capture the inelastic response of both reinforced concrete and steel components.

Selected significant response parameters, e.g., interstory drift and peak floor acceleration, are examined to assess the structural performance of the investigated symmetrical models. Response plots of dimensionless parameters are shown to obtain an objective comparison between mixed and conventional RC structures.

The results provide insight into the influence of symmetric mixed construction on seismic response, revealing differences in stiffness, ductility, and overall performance compared with traditional RC systems. The findings contribute to a clearer understanding of the behavior of symmetric mixed RC–steel structures and may support the future development of seismic design provisions that explicitly address such building typologies.