Behavior of normal and high strength confined concrete columns with and without stubs

An experimental research to investigate the behavior of normal-strength concrete (NSC) and high-strength concrete (HSC) columns confined with rectilinear ties was undertaken. Variables considered were axial load level, steel configuration, amount of lateral steel, concrete strength, and presence of stub. The primary objectives of this research were to relate column performance to various design parameters, evaluate the confinement provisions of the ACI Code, and suggest needed changes in the design.; Nine large size specimens, three HSC prismatic and six NSC nonprismatic, were tested under cyclic lateral load while subjected to constant axial load. The HSC specimens were 12 x 12 x 90 in. (305 x 305 x 2,438 mm) whereas NSC specimens were 12 x 12 x 58 in. (305 x 305 x 1,437 mm) columns with 20 x 30 x 32 in. (508 x 762 x 813 mm) stubs. Results of three HSC nonprismatic specimens recently tested at the University of Houston were also effectively used in the analysis. In the test program, applied axial load varied between 0.47f{dollar}sb{lcub}rm c{rcub}spprime{dollar}A{dollar}sb{lcub}rm g{rcub}{dollar} and 0.88f{dollar}sb{lcub}rm c{rcub}spprime{dollar}A{dollar}sb{lcub}rm g{rcub}{dollar}, lateral steel content varied from 1.30% to 3.06%, and concrete strength ranged from 4,540 psi. (31.3 MPa) to 8,570 psi. (59.1 MPa). Three different steel configurations were used.; Test results indicated significant improvement in strength and ductility due to an increase in lateral steel content for both NSC and HSC columns. Ductility reduced drastically due to increase in axial load. Buckling of longitudinal bars and opening of 90{dollar}spcirc{dollar} hooks of crossties affected column performance adversely. HSC columns showed significantly less ductility than NSC columns. The presence of stub imparted flexural strength enhancement (about 20% of theoretical capacity) to the adjacent critical sections. Section moment capacity increased by up to 60% due to confinement in NSC columns. Sheikh and Uzumeri model and modified Kent and Park model predicted test results reasonably well.; The experimental results strongly suggest that the Code required amount of lateral steel may be excessive at low axial load levels but unconservative at high axial load levels. A design procedure was suggested which relates the required amount of lateral steel in tied columns to axial load level and column performance. The proposed method is calibrated against a large number of realistically-sized specimens, which emphasized its reliability. Limiting conditions for the use of certain steel configurations were also suggested.