Strength analysis of concrete-encased cellular steel columns

This research investigates the compression behavior of bare cellular steel columns and concrete-encased cellular steel (CECS) columns subjected to concentric and eccentric loadings. First, the experimental study of the cellular steel and CECS columns was conducted in the laboratory. For the cellular steel columns subjected to concentric loading, the failure mode of the bare cellular steel columns was local buckling at both web and flanges at the hole section. All cellular steel columns exhibited yielding and hardening behavior. The cellular columns had the average yield loads less than the parent column by 15 %. For the CECS and CES columns subjected to concentric loading, the failure mode and load – deformation relationships were similar with the CES columns having a similar stirrup spacing. The failure of CECS and CES columns in this research was cover concrete spalling and buckling of the longitudinal rebars at the maximum loads. The CECS columns had the averaged maximum loads less than the CES column by 3 – 6 %. For the cellular steel columns subjected to eccentric loading, the failure mode was local buckling at compression web and flange at the hole section. The cellular columns had the yield loads slightly less than the parent column by 4 % for large eccentricity in this research. For the CECS and CES columns subjected to eccentric loading, the failure mode was concrete crushing at compression side at mid-height at the maximum loads followed by the failure of concrete at tension side. Second, the analytical models were proposed to predict the load – strain relationships of the cellular steel columns and CES columns. In addition, the equations were proposed to predict the yield load and axial stiffness of the cellular steel columns and the maximum loads and axial stiffness of the CECS columns. Finally, the plastic stress distribution and modified AISC 360-16 methods for the strength interaction diagram of the cellular steel and CECS columns were proposed. The proposed strength interaction diagrams show that the cellular and CECS columns had higher strength than the parent columns at high load eccentricity.