Compression field modeling of confined concrete: Constitutive models

It has been widely recognized that the behavior of confined concrete depends upon the level of confinement. Brittleness or ductility is a function of the state of compressive stresses, unconfined concrete strength, volumetric expansion, and concrete softening. Constitutive models for strength enhancement, concrete dilatation, and a new stress-strain relationship for concrete in triaxial compression are proposed. The load-carrying capacity of confined concrete is predicted by utilizing an Ottosen-type surface with newly developed coefficients that account for a wide range of confinement levels (lateral pressures up to 100% of the unconfined concrete strength) and unconfined concrete strengths from 20 to 130 MPa. Concrete dilatation is modeled as a function of the lateral pressure ratio and concrete strength and can reach values beyond the limit of uncompressibility. Experimental results are used to corroborate the new models at the material level, producing accurate agreement.