Nonlocal microplane model for damage due to cracking

As it is now generally accepted, finite element analysis of distributed softening damage in quasi-brittle structures such as concrete structures cannot be based on a classical, that is, local, constitutive model of the material. Such a model introduces incorrect excessive localizations, spurious size effect and spurious mesh sensitivity in finite element computations. To overcome these problems, the constitutive model must be supplemented with some sort of the so-called localization limiter. One effective type of the localization limiter is the nonlocal continuum. The present paper reviews two recent developments, one dealing with the formulation and application of a special new type of nonlocal model for materials such as concrete, which is derived physically from microcrack interactions, and numerical application of this model in finite element analysis. The paper also briefly summaries a new nonlinear triaxial damage model based on the microplane concept utilizing the new idea of stress-strain boundaries.