Studies on high-strength concrete columns under eccentric compression

The results of a research program on the behavior and strength of high-strength concrete columns under eccentric compression are presented. Thirty-six columns were tested; the variables were column cross section, eccentricity of load, longitudinal reinforcement ratio, and concrete compressive strength. The columns were either 300 x 100 or 175 x 175 mm (12 x 4 or 7 x 7 in) in cross section with an effective length of 1680 mm (66 in.). They were reinforced with either four or six deformed bars of 12 mm (0.5 in.) diameter and yield strength of 430 MPa (62 ksi). Concrete cylinder compressive strength at the time of testing was either 58, 92, or 97 MPa (8410, 13,340, or 14,065 psi). Eccentricity of load was varied in the range from 0.086 to 0.4 times the column depth and the rectangular specimens were loaded about the minor axis. Lateral reinforcement was provided by 4-mm (0.16-in.) closed ties with a minimum yield strength of 450 MPa at 60-mm (2.36-in.) spacing. A theory was developed to predict the load-deflection behavior and the failure load of high-strength concrete columns under eccentric compression. The theory is based on a simplified stability analysis and a stress-strain relation of high-strength concrete in compression. The average ratio of test failure load to predicted failure load is 1.13 with a coefficient of variation of 10 percent.