Eccentric Axial Load Testing for Concrete-Encased Steel Columns Using 800 MPa Steel and 100 MPa Concrete

Seven concrete-encased steel columns using high-strength steel (nominal yield strength $f_{ys}=913$ and 806 MPa) and high-strength concrete (cylinder compressive strength $f_c^{\prime }=94$ and 113 MPa) were tested to investigate the eccentric axial load-carrying capacity and the deformation capacity. The test parameters were full or partial concrete-encasement, the eccentricity of the axial load, and the effect of lateral reinforcement. Because the yield strain ($\approx 0.004$) of the high-strength steel is greater than the ultimate compressive strain ($\approx 0.003$) of the concrete subjected to short-term loads, the current study focused on the effect of early concrete crushing on the behavior of the composite columns. The test results showed that in the case of inadequate lateral confinement, the load-carrying capacity was limited by the early crushing of concrete. However, because of the high-strength steel section, all test specimens showed ductile flexural behavior after the delamination of the concrete. The test results were compared with the predictions by nonlinear numerical analysis and current design codes.