1. Introduction — Field of application

The law of behavior ENDO_ISOT_BETON aims to model the behavior of fragile elastic concrete as simply as possible. It can be seen as an extension of law ENDO_FRAGILE [R5.03.18] (with which it maintains a certain proximity of formulation) for Civil Engineering applications.

As with law ENDO_FRAGILE, the material is isotropic. Stiffness may decrease, with the loss of stiffness measured by a scalar varying from 0 (healthy material) to 1 (totally damaged material).

On the other hand, unlike ENDO_FRAGILE, the loss of stiffness distinguishes traction from compression, to favor tensile damage. In addition, this loss of stiffness can disappear by returning to compression, this is the phenomenon of restoration of rigidity when reclosing. It should also be noted that this damage law aims to describe the failure of concrete under tension; it is therefore not at all suitable for describing the non-linear behavior of concrete under compression. It therefore assumes that the concrete remains in a state of moderate compression.

Law ENDO_ISOT_BETON has softening, which generally leads to a loss of ellipticity of the equations of the problem and consequently to the location of the deformations, resulting in a pathological dependence on the mesh.

Finally, the softening nature of the behavior also leads to the appearance of instabilities, physical or parasitic, which result in snap-backs on the global response and make load management essential in static terms. PRED_ELAS [R5.03.80] control then appears to be the most suitable load control mode.