The concrete smeared crack model is used to simulate the plain concrete. The concrete-smeared  crack model assumes that the monotonic load is applied to concrete under low confining pressure. The low confining pressure corresponds to the stress less than 1/5 to 1/4 of the maximum compressive strength of concrete. For reinforced concrete, the embedded elements are used. In this case, effects such as bond slip from the interface of concrete and steel are considered through tension stiffening. The concrete smeared crack model simulates the compression part of concrete using a typical isotropic elasto-plastic model, and the tensile part of concrete is simulated using a smeared crack model. The smeared crack model is a method of simulating the crack by adjusting the stress and stiffness at the integration point, without reconfiguring the mesh. In the smeared crack model, the band-width obtained based on the size of the element is reflected in the crack behavior to avoid mesh dependencies (Bazant and Oh 1983). The square root of an area for a two-dimensional element and the cubic root of a volume for a three-dimensional element are the crack width of the element. For the higher order element, the half of the square root and the cubic root are the crack width. The tensile/compression uniaxial behavior of the concrete smeared crack model is shown in the figure below.

Uniaxial Behavior Of Concrete Smeared Crack

Tensile Behavior

Cracks occur when the stress is outside the crack detection surface, a type of yield function. If a crack occurs, the stress is returned using an implicit backward Euler method, and the direction of the maximum principal strain is the direction of the crack. This direction is stored to simulate the anisotropy by cracking in subsequent analyses. Since the orthogonal fixed crack model is used in the smeared crack model, the subsequent crack shall be in a direction orthogonal to the existing crack direction and up to three in the case of the three dimensional model. If the elastic strain in the direction of the crack is tensile after the crack has occurred, it behaves as damaged elastic and it is considered that the crack is closed when it is compressed.

Tensile Behavior of Concrete Smeared Crack