Behavior of spirally reinforced high strength concrete columns under axial loading

grantor: University of TorontoAn experimental investigation was conducted to study the behavior of spirally reinforced high strength concrete (HSC) columns subjected to axial compression loading. The main objective of the experiment was to investigate the effects of the volumetric ratio of spiral steel, the spiral spacing, the specimen size and the concrete strength on the strength and ductility performance of confined concrete. Behavior of the cover concrete, spiral reinforcement steel, and longitudinal reinforcing bars were also investigated to gain insight into the overall behavior of HSC columns. A total of 32 spirally reinforced HSC columns were tested, including ten 254 mm diameter columns with concrete strength f'c of 69.7 Mpa, nine 203 mm diameter columns with concrete strength f'c of 69.7 MPa, and thirteen 203 mm diameter columns with concrete strength f 'c of 89.8 MPa. Overall height of each specimen was four times the diameter. All of the specimens were reinforced longitudinally with five deformed reinforcement bars and laterally by various amounts of spiral reinforcement. An increase in the volumetric ratio of spiral steel resulted in increases in the strength and ductility of confined HSC, with the improvements in ductility being more pronounced. Reductions in spiral spacing resulted in improved strength and ductility of confined HSC when the volumetric ratio of spiral steel was sufficiently large. Increases in concrete strength were found to result in decreases in the peak strength enhancement, axial strain at peak strength, spiral stress at peak strength, and deformability of the specimens. Larger diameter columns achieved better participation of the cover concrete shell and had larger strengths at low axial strains. Cover concrete began spalling at lower concrete strengths and at earlier axial strains than expected in the columns with f'c of 89.8 MPa.M.A.Sc