1. Introduction

In the context of studies of the long-term behavior of concrete structures, a preponderant part of the deformations measured on structures concern the delayed deformations that appear in concrete during its life. They include early age withdrawals, desiccation withdrawal, clean creep, and desiccation creep.

The model presented here is dedicated to the modeling of deferred deformation associated with creep, clean and desiccation. Clean creep is, in addition to desiccation creep, the proportion of creep in concrete that would be observed during a test without exchanging water with the outside. Experimentally, creep concrete has an aging viscoelastic behavior. The observed creep deformation is proportional to the loading stress and depends on temperature and humidity. The aging aspect and temperature dependence are not taken into account by this law.

Clean creep. The first concrete creep model introduced previously in Code_Aster (see for example [R7.01.01] and [bib4]) was developed in order to predict longitudinal creep deformations under uniaxial stresses. The generalization of this model, in order to take into account a state of multiaxial stresses, is then carried out by means of an arbitrary Poisson’s ratio of creep, which is constant and equal to, or close to, the elastic Poisson’s ratio. However, the determination a posteriori of the effective creep Poisson’s ratio shows its dependence on the loading path. In addition, the concrete of certain structures in Park EDF, such as nuclear reactor confinement enclosures, is subject to a state of biaxial stresses. This observation led to the development of the proper creep deformation law UMLV (University of Marne-la-Vallée, partner in the development of this model) for which the Poisson’s creep ratio is a direct consequence of the calculation of the main deformations.

Desiccation creep. The model proposed here is that of Bazant [bib6]. It is a purely viscous law.

In Code_Aster, the creep model shown here is used under the name BETON_UMLV.