  In the present paper a plastic-damage model for concrete is discussed. Based
on the fact that for isotropic materials the elastic trial stress and the
projected plastic stress states have the same eigenvec-tors, the loading
surface is formulated in the principal stress space rather than using the
invariants of stress tensor. The model assumes that the directions of
orthotropic damage coincide with principal directions of elastic predictor
stress state (motivated by coaxial rotated crack model). Due to this
assumption, the load-ing surface and the closest point projection algorithm can
still be formulated in the principal directions. The evolution of the inelastic
strain is determined using minimization principle. Damage and plastic parts of
the inelastic strain are separated using a scalar parameter, which is assumed
to be stress dependent. The paper also discusses an effective numerical
implementation. The performance of the model is demonstrated on one
illustrative example.
