Abstract
Scalar damage models are very often implemented in computational analyses in order to predict the response and failure modes of concrete and reinforced concrete structures. In most situations, however, damage is not isotropic but has preferential directions. Therefore, there have been many questions about the pertinence and range of applicability of isotropic, scalar, damage models for describing a degradation process which is strongly geometrically oriented. In order to assess what are the limitations of such a simplifying assumption, a comparative study is presented. The constitutive relations used for this purpose derive from the same class of models with a gradual enhancement of the description of damage. The scalar damage model is compared to another model where damage-induced orthotropy is described, with the possibility of rotation of the principle axes of orthotropy. Both models incorporate crack closure effects and a plasticity damage coupling. Structural analyses on bending beams, compression-shear and tension-shear concrete panels are presented. Although it may appear to be simplistic, the scalar damage model provides accurate predictions when failure is mainly due to uniaxial extension. Crack closure introduces an additional anisotropy which is important in compression-shear problems. Finally, damage-induced anisotropy seems important when failure is due to multiaxial extensions, such as in shear-tension problems. Copyright © 1999 John Wiley & Sons, Ltd.
Highlights
Quasi-brittle materials such as concrete exhibit a non-linear stress}strain response mainly because of microcracking
Damage-induced anisotropy is too delicate to characterize experimentally. It increases the number of model parameters to be experimentally determined, at least in the context of phenomenological model where damage is a second- or a fourth-order tensor
It is legitimate to argue that the de"nition of a damage variable should incorporate some directional information, it is interesting to sort out situations where an isotropic model may yield good predictions in structural analyses
Summary
Quasi-brittle materials such as concrete exhibit a non-linear stress}strain response mainly because of microcracking. In Ladeveze's proposal, it is already stated that the de"nition of the damage surfaces should be envisioned with respect to experimental observations: without any other discriminating data, the simple knowledge of a uniaxial response of the material (axial strain}axial stress) cannot provide anything but a one scalar isotropic damage model. The additional knowledge of the axial strain vs transverse strain curve yields a two scalar isotropic damage model It is purely phenomenological, this method relates the local state of damage in each direction to the overall mechanical response of the material. The remaining part of the paper will be devoted to comparisons between the isotropic and anisotropic damage models from the viewpoint of structural analysis
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