Eccentric axial load capacity of high-strength steel-concrete composite columns of various sectional shapes

Two concrete-filled steel tube columns and four concrete-encased steel columns using high-strength steel (yield strength fys=913, 806, and 812 MPa) and high-strength concrete (compressive strength fc′=94, 113, 104, and 184 MPa) were tested to investigate the effect of various sectional shapes and configurations on the eccentric axial load carrying capacity. This study focused on maximizing the contribution of the high-strength steel, preventing early crushing of the concrete (1) by using steel tubes or closely spaced ties for lateral confinement, (2) by using ultra high-strength (200 MPa) concrete with a high-crushing strain, and (3) by placing L-shaped steel sections at the corners of the cross section. The test results showed that the steel tube successfully restrained early concrete crushing and developed its full plastic stress; unlike expectation, early crushing occurred in the ultra high-strength concrete column; and the concrete-encased L-section column had higher peak strength and flexural stiffness than the conventional concrete-encased H-section columns. For the design of the concrete-filled columns, the conventional plastic design method is applicable, whereas the strain-compatibility method should be used for the design of the concrete-encased columns with limited lateral confinement.