Orthotropic model of concrete for triaxial stresses

An orthotropic model to predict the ascending and descending parts of the stress-strain curves of concrete subjected to biaxial or triaxial compressive stresses is presented. The stress-induced orthotropic material properties are expressed in terms of six constants in the compliance matrix. The six material constants are expressed as functions of stress invariants at ultimate strength. The proposed orthotropic constitutive model depends on the knowledge of the three principal stresses at the maximum strength, which are obtained through the use of a strength criterion (which is sensitive to all the three stress invariants). For predicting the ascending and descending parts of the multiaxial stressstrain curves, the six orthotropic material constants in the compliance matrix are continuously changed with the help of a "fracturing index" parameter. The proposed constitutive model compares favorably with the available experimental data under multiaxial stresses.