Seismic performance of externally stiffened ring connections between concrete-filled steel tubular columns and reinforced concrete beams

Abstract

Concrete-filled steel tubular (CFST) columns are widely used in high-rise and long-span structures due to their high strength, stiffness, and ductility. However, conventional CFST column–reinforced concrete (RC) beam connections usually involve complex detailing, column capacity reduction, and inefficient construction. This study proposes a novel externally stiffened ring connection to overcome these drawbacks. A total of eight 1:5 scaled specimens were tested under low-cycle reversed loading, including welded and lapped configurations. The effects of axial compression ratio (0.33 , 0.50) and corbel length (120 mm , 240 mm) were systematically investigated. Nonlinear finite element (FE) models using ABAQUS were established to validate test results and reveal force-transfer mechanisms. Results indicate that all specimens achieved ductility coefficients greater than 5, satisfying seismic design requirements. Welded connections exhibited full spindle-shaped hysteretic loops, stable stiffness degradation, and superior energy dissipation, owing to continuous force transmission through welding. Lapped connections with short corbels experienced premature concrete splitting and low material efficiency, while those with long corbels showed improved ductility but lower economic efficiency. The FE models adopting the concrete damaged plasticity model and layered simulation accurately reproduced failure modes and backbone curves, with errors within 10%. This study confirms the effectiveness of the externally stiffened ring system. Welded connections are recommended for practical CFST frames, providing balanced seismic performance, constructability, and design simplicity.