CONFINEMENT OF HIGH-STRENGTH CONCRETE IN COMPRESSION MEMBERS

Abstract

The objective of the present investigation is to experimentally establish the similarities or differences in behaviour between normal and high-strength spirally confined concrete under uniaxial compression with particular reference to strength gain, stress-strain curves and ductility. High-strength concrete tends to be brittle when loaded to failure, lacking the plastic deformation typical of lower-strength concretes. Lateral confinement, such as provided by spiral reinforcement greatly improves both the compressive strength and the ductility of lower-strength concrete, leading to the expectation that similar benefits would also occur in high-strength concrete. The experimental programme consisted of casting of one hundred and sixty-two cylindrical specimens of size 150 x 300 mm. These include both plain and spirally confined specimens of three grades of concrete. Two types of steel, 6 mm dia. mild steel and 8 mm dia. for steel (HYSD) were used for spirals of different pitches. All specimens were tested at 28 days under uniaxial compression and stress-strain data was obtained. The data was processed and comparison studies were carried out for increase in strength, ductility and toughness of the three grades of concrete with varying lateral confinement. The experimental data for high-strength concrete has also been compared with the theoretical model proposed by Mander et al. and relevant conclusions drawn from the study.