Axial compression behavior of hybrid fiber reinforced concrete encased cold‐formed steel composite columns: An experimental and theoretical investigation

Concrete encased steel composite columns conventionally comprise an encased steel section, reinforcement cage, and surrounding concrete. However, reinforcement congestion may create difficulties during concrete placement and compaction. This study examines the axial compression behavior of silica fume modified hybrid fiber reinforced concrete encased cold‐formed light gauge steel composite columns. Three concrete systems, namely conventional concrete (CC), steel–polypropylene hybrid fiber reinforced concrete (SP), and steel–coir hybrid fiber reinforced concrete (SC) incorporating sodium carbonate treated coir fibers, were considered. Channel, Z, and hat‐shaped cold‐formed steel sections with and without lip configurations were tested under concentric axial loading. Compared with CC specimens, SP and SC specimens exhibited increases in ultimate axial capacity of 11.8%–14.1% and 19.0%–23.0%, respectively. The incorporation of lip stiffeners increased axial capacity by 1.7%–3.2%, while the SC‐H‐L specimen achieved the highest load carrying capacity of 874.38 kN. A proposed ultimate load prediction model incorporating section geometry, lip configuration, and hybrid fiber interaction effects produced predicted‐to‐experimental capacity ratios ranging from 0.976 to 1.071. The results indicate that both hybrid fiber reinforcement and cold‐formed steel section configuration influenced the axial compression behavior of the composite columns.