The tyaditional unified viscoplasticity constitutive model is only applied for the constitutive analysis of metallic materials. A coupled viscoplasticity damage constitutive model for concrete is developed within the framework of irreversible thermodynamics; and an expression for the Helmholtz free energy function involving the state variables of mix hardening is given. The hardening model of concrete is analyzed; and the flow equation and the evolution equations of the state variables are derived from a non-associated flow potential function including the state variables of kinematic hardening and isotropic hardening. The results of numerical simulation show that the represented model can reproduce the strain-rate sensitive characteristic

inelastic volume dilatancy

softenting-hardening under loading; and strain-softening induced by damages and fractures.