Axial compressive behavior of steel fiber reinforced concrete-filled square steel tube stub columns

This study aims to assess the influence of steel fiber on the mechanical property of concrete-filled square steel tube (CFSST) stub columns. A total of 36 specimens, with different concrete strength grades (C = 40 MPa, 50 MPa or 60 MPa), various steel tube thicknesses (t = 3 mm, 3.75 mm or 4.5 mm) and diverse steel fiber volume contents (Vf = 0%, 0.6%, 1.2% or 1.8%), are conducted under axial compressive loading. Failure modes, ultimate loads, load-displacement behavior and relative load-strain behavior are discussed. Moreover, a finite element (FE) model is proposed to investigate the reinforcing mechanism of steel fibers in CFSST columns. The test results show that the ultimate bearing capacity of CFSST columns slightly increases with the increasing of steel fiber volume content, but the energy dissipation capacity and ductility are visibly improved. However excessive steel fibers (exceeding 1.2% in this study) may cause a negative effect. FE analysis demonstrates that steel fibers with a moderate amount not only postpone the failure of concrete core, but also improve the carrying loads of concrete core at ultimate state. Finally, a design formula is put forward for the ultimate bearing capacity of CFSST stub columns.