Seismic behavior of concrete-filled steel tubular (CFST) column-partially encased composite (PEC) beam connections

Efficient, rapid-assembly column–beam connections are critical for improving seismic performance and construction productivity in concrete-filled steel tubular (CFST) column–partially encased composite (PEC) beam structures. This study evaluates the seismic behavior of three full-scale CFST column–PEC beam connection specimens: specimen B1 (cast-in-place), specimen B2 (post-cast), and specimen B3 (cast-free thickened). Experimental quasi-static cyclic tests were conducted to characterize lateral strength, failure mechanisms, and energy dissipation; numerical finite element (FE) models and theoretical capacity predictions were also developed for validation. Specimens B1 and B2 exhibited similar localized concrete cracking and flange tearing, whereas specimen B3 demonstrated a more ductile response with damage propagating into the PEC beam. Specimen B3 achieved the highest lateral strength (233 kN), cumulative energy dissipation (11,904.84 J) and maintained post-ultimate ductility index (1.00), outperforming specimen B1 by 268.6 % in energy dissipation and 53 % in lateral strength. Because specimen B2 differed from specimen B1 by only 1.97 % in ultimate strength (152 vs 155 kN) and 5.5 % in initial stiffness (5.82 vs 5.50 kN/mm), only specimens B1 and B3 were used for FE calibration/validation. The calibrated FE models showed small discrepancies (3.8 % for lateral strength, 5.5 % for ductility) and accurately reproduced the failure patterns. Finally, bending capacity predictions from T/CECS 719–2020, AISC 360-16, YB 9082-2006, and a newly proposed model were compared against test results. The proposed model achieved the highest accuracy (test/theory = 0.96) with a low coefficient of variation (Cov) of 0.09. The findings support the use of cast-free thickened CFST column–PEC beam connections to enhance seismic resilience of prefabricated high-rise systems.