Seismic Design and Verification of Hybrid Steel-GFRP-Reinforced Concrete Frames: Analytical and FEM Approaches

Abstract The increasing interest in durable, corrosion-resistant, and seismically efficient structural systems has motivated the development of hybrid reinforcement solutions that combine steel with fiber-reinforced polymers. This study proposes and evaluates a comprehensive design framework for RC members employing hybrid steel and glass fiber–reinforced polymer (GFRP) reinforcement, applied to the beam, column, and exterior beam–column joint of a representative residential moment-resisting frame building. The design is carried out in accordance with both European and US codes, integrating provisions from these codes and adapting/extending them where necessary to capture the coexistence of ductile and brittle reinforcement materials. Following capacity-based design procedures, flexural and shear verifications are performed for all structural components. To support and validate the analytical design assumptions, a detailed FEM analysis investigation is conducted. The numerical model is calibrated using experimental results from a well-documented RC joint test reported in the literature and subsequently applied to the hybrid beam–column joint developed in this study. The calibrated model enables the assessment of stress transfer mechanisms, joint shear behavior, and the interaction between steel and GFRP reinforcement under seismic-type loading. Results demonstrate that hybrid reinforcement can successfully combine the ductility contribution of steel with the corrosion resistance and elastic behavior of GFRP, achieving performance levels comparable to or exceeding those of conventional RC members. The numerical analyses confirm the validity of the design hypotheses and highlight the potential of hybrid systems as a reliable and code-consistent solution for seismic applications.