EFFECT OF CONFINEMENT ON STRESS - STRAIN CHARACTERISTICS OF CONCRETE

Abstract

This covers a theoretical and experimental investigation on the effects of providing transverse reinforcement to concrete on its stress-strain behaviour. The thrust is on comparing the beneficial effects of the same degree of confinement on concretes of strengths ranging from low level to higher level. In order to make a proper analysis of the flexural resistance of reinforced concrete sections with steel confinement, the basic data needed are the stress-strain characteristics of the concreteiso confined. Tests have shown that confinement of concrete by suitable arrangement of transverse reinforcement results in a significant increase in both the strength and the ductility (slope of the descending branch of the stress-strain curve) of compressed concrete. Therefore, it is important to have accurate information concerning the complete stress-strain curve of confined concrete and how this property varies with the variables such a grade of concrete, volume of confining steel and its spacing. The experimental programme consisted of casting of cylinderical specimens of three grades of concrete confined with 6mm dia mild steel hoops at different spacings. 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, increase in ductility and toughness characteristics of the three grades of concrete with varying lateral confinement. The experimental stress-strain data has also been compared with the theoretical model proposed by Mander and observations made.