How is nonlinear concrete behavior modeled in finite element analysis?

Nonlinear concrete FEA uses constitutive models capturing: (1) Compression - stress-strain with softening post-peak, confinement effects (Mander model), (2) Tension - cracking with tension stiffening (smeared or discrete crack approaches), (3) Shear - aggregate interlock, dowel action, (4) Biaxial/triaxial stress states - failure surfaces (Kupfer, Willam-Warnke), (5) Damage and plasticity - combined models for cyclic loading. Element types include solid elements, shell/plate elements, and beam/frame elements. Mesh sensitivity addressed through regularization techniques. Commercial software: ABAQUS, DIANA, ATENA.