Constitutive Model for Reinforced Concrete

A numerical model is proposed for reinforced-concrete behavior that combines some commonly accepted ideas for modeling plain concrete, reinforcement, and interaction behavior (e.g., due to bond) in a consistent manner. The basic idea is that the total stress that exists in a reinforced-concrete element can be rigorously decomposed into individual contributions of the plain concrete, the reinforcement, and the interaction between these constituents. The behavior of plain concrete is governed by fracture-energy–based formulations both in tension and in compression. In this fashion, mesh-independent results can be obtained with respect to the limit load. In the presence of reinforcement, the fracture energy is assumed to be distributed over a tributary area that belongs to a crack. The crack spacing is estimated using accepted CEB-FIP recommendations. The reinforcement is modeled using a standard elastoplastic model, and for the stress contribution that results from the interaction between concrete and reinforcement a trilinear function is adopted. Although the model allows for inclusion of dowel action, this contribution proved unimportant in the structures considered. The application of the model to reinforced-concrete panels and shear walls gives good simulations of the failure behavior.