Axial local bearing behavior of circular reinforced concrete filled steel tube stub columns

In this work, the axial local compression of circular reinforced concrete-filled steel tube (CRCFT) stub columns is studied. Sixteen specimens, including one circular reinforced concrete stub column (CRCC) specimen and fifteen CRCFT specimens, were prepared, considering different variables, such as the local compression area ratio beta, sectional steel ratio alpha, volume stirrup ratio rho v, longitudinal reinforcement ratio rho, and concrete strength fc. The axial local compression of specimens were experimentally investigated in terms of the damage process, failure mode, load-displacement relationship, ultimate bearing capacity, stiffness, deformation capacity, and strain characteristic. The finite element model of the CRCFT was also developed and validated. The parametric analysis of the local compression area ratio beta, sectional steel ratio alpha, and volume stirrup ratio rho v facilitated the further investigation of the axial local compression behavior of CRCFT. The results showed steel tube buckling and concrete shear failure exhibited by CRCFT specimens. With the increasing local compression area ratio beta, the ultimate bearing capacity reduced by 3.6-47.9 %, whereas the local compression strength improvement coefficient beta cl increased by 11.8-273.9 %. With the increase in section steel ratio alpha and volume stirrup ratio rho v, the ultimate bearing capacity, stiffness, and deformation capacity were improved. Longitudinal reinforcement ratio rho and the concrete strength fc also influenced the stiffness of CRCFT specimens. A simplified calculation method for the ultimate bearing capacity of CRCFT specimens was also presented.