[en] In order to evaluate the safety margins vis-a-vis the ruin of reinforced concrete structures like nuclear reactor containment buildings, nonlinear analysis using finite elements techniques are required. For this purpose, material models have already been proposed for concrete, based on an elasto-plastic approach. However, they did not include damage effects which are observed and were based on the hypothesis of a perfect closure of open cracks in case of loads reversal. In this paper, a new model is proposed, in which special care has been given to the treatment of cracking; firstly the behaviour of the concrete under traction loads is described by a multi-potential elasto-plastic approach, coupled with an evolution of the elastic properties due to damage. Secondly, a residual crack opening is introduced, in order to represent the transition from traction to compression in case of load reversal, as observed in some experiments. Some simple examples of application of the model will be given in the paper. (author)