BUCKLING BEHAVIOR OF SLENDER HIGH-STRENGTH CONCRETE COLUMNS

A numerical method for predicting the behaviour of a reinforced concre te column is proposed, using the layered finite element method. To inv estigate the effects of concrete strength and longitudinal steel ratio on the ultimate load and axial force-bending moment relation of a col umn, a series of tests was carried out for 30 tied reinforced concrete columns with a 80 mm square cross-section a nd three slenderness rati os of 10, 60 and 100. Th ree different concrete strengths of 25.5, 63. 5 and 86.2 MPa, and two different longitudinal steel ratios of 1.98 an d 3.95% were used. The boundary conditions at the ends were both hinge d and end eccentricities (24 mm) were equal and of the same sign. Expe rimental results revealed that the ultimate load for a short high-stre ngth concrete column was significantly increased but not for a slender column. The possibility of stability failure for a slender column was increased with the increase of concrete strength. The increment of ul timate load due to increase in longitudinal reinforcement for the shor t column was less than for the slender one, and the heavier reinforcem ent for the slender column led to a more stable column. The predicted behaviours of the concrete columns by the numerical method proposed he rein show good agreement with the test results, they also show that th e ACl's moment magnifier method may be unconservative for very slender high-strength concrete column.