A Generic Damage-Plasticity Model for Confined Concrete in Various Stress States

Confined concrete has garnered significant attention owing to its advantages, such as enhanced strength, improved deformation capacity, and associated benefits when used in engineering structures. Although existing constitutive models reasonably predict the behavior of actively and passively confined concrete columns under axial compression, they are not designed to model concrete behavior in various stress states encountered in practice, including eccentrically compressed concrete columns passively confined by fiber-reinforced polymer (FRP) sheets. Accordingly, this study presents a new three-dimensional damaged-plasticity model for confined concrete under various stress states, based on the well-known Lubliner–Lee damaged-plasticity model. A key advancement involves a capped potential surface with a bulged triangular deviatoric trace under compression-dominated stress states and a Drucker–Prager potential surface under tension-dominated stress states, connected by a smooth transition. The potential surface, along with a properly designed yield surface, hardening rule, and evolution law for internal variables, makes the proposed model well suited to capturing concrete behavior under various stress states, including triaxial compression, tension–compression, and loading–unloading. The constitutive model is first validated against monotonic and cyclic axial-compression data for actively and passively confined concrete and then verified using eccentric-compression results for FRP-confined concrete. The validation confirms the capability and accuracy of the proposed model to capture concrete behavior under various stress states.