Numerical Biaxial Characterization for Concrete

A biaxial characterization for concrete as a nonlinear inelastic material is developed from the most complete experimental biaxial information available. The representation of concrete behavior used bears many similarities to cumulative damage concepts. For computational ease, the continuous accumulation of damage is replaced by four damage regions in which constant parameters are assumed to define the behavior. The initial characterization is developed in stress space and then transformed to strain space to avoid nonuniqueness of representation. The method by which the representation is used to predict an incremental stress-strain law for an arbitrary change in strain state is described to demonstrate its suitability for finite element analysis. To derive such constitutive relations in biaxial form requires only a multilinear approximation of the uniaxial compression stress-strain behavior, the biaxial failure stress (or strain) envelope, and values of Poisson's ratio. The representation is compared to available biaxial test information and shown to describe the essential characteristics of biaxial response.