Concrete-filled steel tube (CFST) columns offer notable advantages over traditional reinforced concrete columns, including improved energy dissipation, strength, and stiffness. This research explores the structural behavior of CFST stub columns under uniaxial compression, focusing on the impact of steel fibers in M30 grade concrete. Nine CFST specimens with different slenderness ratios were tested to examine their axial load behavior. The study evaluates variables such as ultimate load capacity, axial load-deformation response, strain characteristics, failure modes, concrete confinement, and axial strength. Tests included hollow and concrete-filled steel tubes (100 mm inner diameter, 3mm thick) at heights of 200 mm, 300 mm, and 400 mm, with slenderness ratios of 1.89, 2.83, and 3.77. Three specimens per ratio (hollow, concrete-filled, and fiber-reinforced) were tested. Vertical deformation, vertical strain, and lateral strain were measured. Confinement factors were 0.708 for plain concrete and 0.574 for fiber-reinforced concrete. Results showed an 8.34% increase in ultimate load capacity for fiber-reinforced concrete at a 3.77 ratio, while other ratios had marginal gains. Fiber reinforcement improved stiffness by 20.48%, 6.25%, and 0.56% for the respective heights, with ultimate load capacities increasing by 0.96%, 2.46%, and 8.34%. Vertical shortening varied, and strength indices decreased with height.

Keywords: Concrete-filled steel tube (CFST), Steel fiber reinforced concrete (SFRC), Load-bearing capacity, Stiffness, Strength enhancement index (SI), Load capacity, Ductility, Poisons ratio.