A true 3D frictional hardening elastoplastic constitutive model of concrete based on a unified hardening/softening function

This paper discusses three hardening modes of a shear-type yield surface and proposes a true three-dimensional (3D) frictional hardening method using the transformed stress. The proposed method reasonably reflects the stress-induced anisotropy of concrete for a wide range of hydrostatic pressures. A unified hardening/softening function is proposed based on the uniaxial compressive stress-strain relationship. The plastic potential function is obtained by studying the influence of linear and nonlinear plastic potential function on the dilatancy, and the relationship between the yield surface and plastic potential surface is analyzed. The loading-unloading criterion suitable for the softening behavior is obtained by transforming the yield function expressed by stress into the one expressed by strain. Furthermore, a true 3D frictional hardening elastoplastic constitutive model is established. The explicit stress integral algorithm and semi-implicit stress integral algorithm are used to implement the numerical computation. Finally, five sets of biaxial and triaxial test results of high-strength and normal-strength concrete are used to verify the established constitutive model.