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. Th e elastoplastic concrete model resorts to an isotropic-hardening descr iption of the prepeak behavior and to a fracture energy-based isotropi c-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 calibrate d from a series of stroke-controlled laboratory experiments that inclu de the direct-tension test and triaxial compression tests at three dif ferent levels of confinement. The predictive capabilities of the propo sed model are assessed with a broad range of experimental data. The is sue of failure on the constitutive level is addressed with the aid of the instability indicator for continuous material branching and the lo calization indicator for the formation of weak discontinuities. The re levance of these two failure diagnostics is evaluated with the experim ental data of the wedge experiment on cylindrical concrete specimens w hen the stress path approaches the failure surface within the cone of instability.