Confinement effects on high-strength concrete

An experimental investigation was conducted on the stress-strain characteri stics of steel sleeve confined high-strength concrete (HSC). The axial load and strains of concrete, and the axial and hoop strains of the confining s teel sleeves were measured. From these measurements, accurate stress-strain relations of the concrete core were produced, along with confinement calcu lations based on von-Mises elastoplastic response of the steel sleeves. Con finements ranging from 5 to 19 MPa were calculated This confinement had a p rofound effect on the strength of concrete, as much as tripling its unconfi ned strength of 70 MPa. The increase in ductility was found to develop slow er for low amounts of confining steel due to a lagging development of confi ning pressure. This was attributed to the reduced tendencies of HSC to exhi bit lateral expansion and the early yielding of the sleeve hoop stresses du e to the biaxial nature of stresses within the sleeves.