Quantification of the seismic design coefficients for composite special moment frames with reinforced concrete columns and steel beams

This paper explores the performance of the reinforced concrete column and steel beam (RCS) structural system at the frame-level, with a focus on evaluating the seismic design coefficients (R-factor, Omega(0), and C-d) using the FEMA-P695 methodology. The RCS system offers a more efficient and cost-effective solution compared to conventional steel and RC moment-resisting frames, with higher damping and lateral stiffness of RC columns and greater energy dissipation capacity of steel beams. Although several experimental and numerical studies have evaluated the performance of the RCS system, most of them have focused on the connection-level. In this study, 32 archetypes are designed with varying building height, span length, concrete strength, gravity load level, seismic load level, and column-beam strength ratio. Nonlinear analytical models are developed for the selected archetypes, and the modeling assumptions are validated through five distinct experimental tests. The models are then subjected to both static pushover and response history analyses, and the seismic design coefficients of the archetypes are evaluated and discussed based on the FEMA-P695 methodology. The results indicate that the design requirements of the RCS system are efficient, providing a high safety margin. However, the level of conservatism is found to be excessively high. Thus, it is possible to use a larger R-factor in the design process or make some relaxations in the design requirements related to this structural system. While further research should be carried out to validate the results, this study shows that as long as the R-factor is less than R = 10, the building can be deemed sufficiently safe for seismic loadings.