FRACTURE ENERGY FORMULATION FOR INELASTIC BEHAVIOR OF PLAIN CONCRETE

A constitutive formulation is presented that covers the triaxial load-response spectrum of plain concrete in tension as well as in shear. The elastoplastic concrete model resorts to an isotropic-hardening description of the prepeak behavior and to a fracture energy-based isotropic-softening description of the postpeak response. To control inelastic dilatancy, a nonassociated plastic flow rule is adopted in regard to the inelastic volume change. The constitutive parameters are calibrated from a series of stroke-controlled laboratory experiments that include the direct-tension test and triaxial compression tests at three different levels of confinement. The predictive capabilities of the proposed model are assessed with a broad range of experimental data. The issue of failure on the constitutive level is addressed with the aid of the instability indicator for continuous material branching and the localization indicator for the formation of weak discontinuities. The relevance of these two failure diagnostics is evaluated with the experimental data of the wedge experiment on cylindrical concrete specimens when the stress path approaches the failure surface within the cone of instability.