Confinement Effects on High-Strength Concrete

An experimental investigation was conducted on the stress-strain characteristics of steel sleeve confined high-strength concrete (HSC). The axial load and strains of concrete, and the axial and hoop strains of the confining steel sleeves were measured. From these measurements, accurate stress-strain relations of the concrete core were produced, along with confinement calculations based on von-Mises elastoplastic response of the steel sleeves. Confinements ranging from 5 to 19 MPa were calculated. This confinement had a profound effect on the strength of concrete, as much as tripling its unconfined strength of 70 MPa. The increase in ductility was found to develop slower for low amounts of confining steel due to a lagging development of confining pressure. This was attributed to the reduced tendencies of HSC to exhibit lateral expansion and the early yielding of the sleeve hoop stresses due to the biaxial nature of stresses within the sleeves.