Anisotropic Initial Damage and Its Effect on Tensile Response of Plain Concrete

Damage is often described as isotropic, implying that a scalar value describes its initial state. However, the prior micro‐cracking pattern at points of an existing building, that is, the initial damage, may be oriented by a preload. The degradation of the Volume Element due to oriented preloads shall be described as anisotropic and represented by a tensorial variable. While this damage variable could be a fourth‐order tensor, a second‐order tensor is chosen as a pertinent approximation, simplifying computations of the model response. This work aims to account for non‐zero anisotropic initial damage states, and analyze their effect on plain concrete tensile response. The anisotropic initial damage is parameterized in two steps: (i) a description of the tensor in its principal basis and (ii) the orientation of its principal basis. Continuum Damage Mechanics simulations are performed for given initial damage tensors. The effect of initial damage on the tensile response of concrete is then quantified on the peak stress and various post‐peak quantities of interest, such as damage invariants (hydrostatic and von Mises equivalent damage) and relative distance to isotropy of the effective compliance tensor. How the anisotropy and orientation of the principal basis of the initial damage tensor affect the mechanical response is analyzed and discussed, based on the two‐step parameterization. This work highlights that the observed discrepancy of tensile responses of concrete or mortar may be attributed to anisotropy and orientation of initial damage states. In particular, orientation is found to be most influential for uniaxial anisotropic initial damage.