Compressive behavior of steel tube reinforced concrete column under eccentric loads

The compressive behavior of steel tube reinforced concrete (STRC) columns under eccentric loads was investigated experimentally and numerically in this paper. Primary parameters included the eccentricity ratio, the concrete-filled steel tube (CFST) area ratio, and the longitudinal rebar ratio. This paper analyzed the impacts of these parameters as well as the failure modes, the full-range compression process, and the strain development. Similar to the reinforced concrete (RC) column, the full-range compression process of STRC column under eccentric loads can be divided into three stages, i.e., elastic stage, elastic-plastic stage (cracking stage), and plastic stage (descent stage). The experimental findings showed that, on the near-load side of the STRC column, the outer concrete crushed, and the longitudinal rebars buckled in compression. Conversely, on the far-load side, the concrete exhibited cracking in tension, and the longitudinal rebars exhibited tension. Finite element (FE) analysis results demonstrated that, similar to a RC column, three distinct failure mechanisms can be identified for STRC columns under eccentric loads, i.e., compression-controlled, balanced, and tension-controlled failures. During the compression process, analyses were conducted on the contact stress between the steel tube and concrete, as well as on the load distribution between the inner CFST and the outer RC. The ultimate load of the STRC column decreased with an increase in the eccentricity ratio, while it increased with larger longitudinal rebar ratio and CFST area ratio. Based on the experimental and FE analysis results, a simplified calculation method was developed to determine the eccentricity reduction coefficient for STRC columns.