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.