INVESTIGATIONS ON HIGH STRENGTH CONCRETE COLUMNS

Abstract

Lateral confinement provided in the form of spiral reinforcement greatly improves the ductility of lower strength columns, 1ding to the expectation that similar benefits would also occur in high strength concrete columns. The purpose of this present investigations was to experimentally establish the similarities or differences in behaviour of high strength concrete short circular columns subjected to different parameters. The parameters include grade of concrete, longitudinal reinforcement, transverse reinforcement and addition of steel fibres. The study included gain in strength, ductility, stress-strain curves and mid-height deflection. High strength concrete is known to be brittle when loaded to failure, confinement increased compressive strength and capacity to sustain large deformations without any strength loss. Axially loaded columns occur rare in practice but understanding the behaviour of columns under axial loads assists in quantifying the parameters affecting column performance. The experimental programme consists of casting of one hundred cylindrical specimens of size 150 mm x 600 mm, which include plain and reinforced specimens. Longitudinal reinforcement of 4 Nos. 8 ntm for steel bars was used and transverse reinforcement provided in the form of spirals or hoops had either 6 mm mild steel bars or 8 mm for steel bars at varying pitches of 25, 50, 75 and 100 mm. The affect of addition of fibres, specimens without longitudinal reinforcement is also studied. All the specimens were tested after 28 days under axial compression. The data recorded were ultimate load, longitudinal and lateral strains and mid-height deflection. Comparison studies were carried out for gain in strength, ductility and mid-height deflection and relevant conclusions drawn from the study.