Three-node triangular constant strain elements are employed to simulate concrete. Higher-order elements are not used for the reason that once concrete is cracked, the cracks represent discontinuities and the use of higher-order elements may cause numerical difficulties by constraining the displacements of intermediate nodes. To effectively cater for the biaxial behavior of concrete, the nonlinear biaxial stress– strain relation is transformed into equivalent uniaxial strains, which is computed from the principal strains as given by: