Plastic Model for Concrete in Plane Stress State. I: Theory

A rate-independent constitutive model for plain concrete on the basis of the bounding surface plasticity theory is formulated. Plastic strain rate is described by three independent plastic mechanisms without using a plastic potential surface. The actual plastic surface degenerates to the current stress point. The bounding surface shrinks in the postcritical state. Separate criteria of loading/unloading are used for the deviatoric and hydrostatic portions of stress rate. Plastic modulus functions are formulated separately for virgin loading/unloading/reloading cases on the basis of experimental data. Three different descriptions of shrinkage of the bounding surface are proposed. The important features of concrete behavior, namely, stiffness degradation, contraction/dilatation phenomenon, and different behavior of concrete in compression and in tension are satisfactorily rendered by this model. The presented model can describe concrete behavior in the plane stress state in the full range of loading including cyclic loadings.