Experimental and analytical study on seismic performance of concrete-filled steel tubular column: partially encased composite beam connections

To enhance seismic resilience and accelerate construction in prefabricated steel–concrete composite buildings, this study experimentally and analytically investigates the seismic performance of concrete-filled steel tubular (CFST) column–partially encased composite (PEC) beam joints. Six full-scale joint specimens representing three connection concepts (steel H-beam, monolithic PEC, and cast-free thickened flange) were subjected to combined axial–lateral quasi-static cyclic loading to evaluate lateral strength, deformation capacity, energy dissipation, stiffness degradation, and failure mechanisms. The results show that the cast-free thickened flange joint exhibited a significantly more ductile and stable hysteretic response compared with conventional steel and monolithic PEC joints, with delayed local buckling and distributed damage. The optimized cast-free configuration achieved the highest average lateral strength (102.8 kN), ultimate drift ratio (1/22), and ductility coefficient (μ = 7.9), corresponding to increases of approximately 13 % in strength, 140 % in deformation capacity, and over 113 % in ductility relative to the steel H-beam reference joints, while maintaining comparable initial stiffness. Its cumulative energy dissipation reached approximately 335 kJ, accompanied by stable post-yield stiffness retention. Nonlinear finite element (FE) models accurately reproduced the experimental hysteresis behavior and damage evolution, with mean test-to-FE ratios of 1.00 for strength, 1.40 for initial stiffness, and 0.70 for displacement capacity. Design-code-based predictions were further evaluated using GB 50010–2010, T/CECS 512–2018, and T/CECS 719–2020. Flexural capacity predictions were conservative, with a mean ratio of (Formula presented), while shear capacity estimates showed good agreement, with a mean ratio of (Formula presented). The results confirm the effectiveness of the cast-free thickened flange joint in improving the seismic performance of CFST column–PEC beam frames, while the validated FE and analytical models provide a sound basis for design and optimization.