The present paper, originated by a thorough study for a Final Thesis [1], deals with the fracture of concrete (and more in general of quasi-brittle materials such as rocks and masonry) through the Finite Element Method. The development of models able to simulate the complex physical behaviour of such a phenomenon is a very peculiar subject, as a “definitive” model, well performing in every condition, doesn’t exist so far. The specific formulations of two distinct three-dimensional continuum models are presented: i) an isotropic scalar damage model and ii) a rotating crack model. i) According to the first model, the loss of integrity of the material is controlled by a single scalar parameter. The resulting damaged stiffness tensor is a scalar multiple of the elastic stiffness tensor (so it decreases proportionally in every direction, independently of the direction of the loading). Constant Poisson ratio is also assumed, as the most general isotropic damage model should deal with two parameters corresponding to the two constants of isotropic elasticity. This model proved to be remarkably stable and very fast in the analysis. Even though it performed well in most cases, the assumption of isotropy is a limitation. ii) On the other hand, the rotating crack model reproduces the anisotropic behaviour of cracking. The implemented version allows the formation of up to three mutually orthogonal cracks which keep aligned with the principal directions (of both stresses and strains). Each crack is initiated as soon as the corresponding principal stress reaches the material tensile strength. Both strain decomposition [2, 3] and damage-like stressstrain relation have been considered. In the first case the total strain is decomposed into bulk-material part (which is assumed to be linear elastic) and inelastic part (due to cracking) and an iterative stress evaluation algorithm is required. Furthermore, damage-like formulation allows direct evaluation of each principal stress for a given relevant principal strain. For both above models, several numerical procedures solving computational problems (also usual in other constitutive laws) are briefly described. The models are implemented into an 8-node volumetric isoparametric element and tested in the analysis of simple but representative structures, for which experimental tests and numerical simulations are also available.

Recent advances in FE modelling of cracking in concrete and quasi-brittle materials / C. Borri; L. Salvatori; W. Zahlten. - STAMPA. - (2003), pp. 0-0. (Intervento presentato al convegno 5TH EUROMECH, Solid Mechanics Conference tenutosi a Thessaloniki, Grecia).

Recent advances in FE modelling of cracking in concrete and quasi-brittle materials

BORRI, CLAUDIO;SALVATORI, LUCA;
2003

Abstract

The present paper, originated by a thorough study for a Final Thesis [1], deals with the fracture of concrete (and more in general of quasi-brittle materials such as rocks and masonry) through the Finite Element Method. The development of models able to simulate the complex physical behaviour of such a phenomenon is a very peculiar subject, as a “definitive” model, well performing in every condition, doesn’t exist so far. The specific formulations of two distinct three-dimensional continuum models are presented: i) an isotropic scalar damage model and ii) a rotating crack model. i) According to the first model, the loss of integrity of the material is controlled by a single scalar parameter. The resulting damaged stiffness tensor is a scalar multiple of the elastic stiffness tensor (so it decreases proportionally in every direction, independently of the direction of the loading). Constant Poisson ratio is also assumed, as the most general isotropic damage model should deal with two parameters corresponding to the two constants of isotropic elasticity. This model proved to be remarkably stable and very fast in the analysis. Even though it performed well in most cases, the assumption of isotropy is a limitation. ii) On the other hand, the rotating crack model reproduces the anisotropic behaviour of cracking. The implemented version allows the formation of up to three mutually orthogonal cracks which keep aligned with the principal directions (of both stresses and strains). Each crack is initiated as soon as the corresponding principal stress reaches the material tensile strength. Both strain decomposition [2, 3] and damage-like stressstrain relation have been considered. In the first case the total strain is decomposed into bulk-material part (which is assumed to be linear elastic) and inelastic part (due to cracking) and an iterative stress evaluation algorithm is required. Furthermore, damage-like formulation allows direct evaluation of each principal stress for a given relevant principal strain. For both above models, several numerical procedures solving computational problems (also usual in other constitutive laws) are briefly described. The models are implemented into an 8-node volumetric isoparametric element and tested in the analysis of simple but representative structures, for which experimental tests and numerical simulations are also available.
2003
5TH EUROMECH, Solid Mechanics Conference
5TH EUROMECH, Solid Mechanics Conference
Thessaloniki, Grecia
C. Borri; L. Salvatori; W. Zahlten
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Utilizza questo identificatore per citare o creare un link a questa risorsa: https://hdl.handle.net/2158/236488
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