1. Introduction

Taking into account of pressure type loads (keyword PRES_REP in the [AFFE_CHAR_MECA] command) poses a number of difficulties in the absence of the hypothesis of small trips. Indeed, unlike the dead charges mentioned in [R5.03.01], the pressure depends on the movements since it is an effort whose direction is normal to the domain; we then speak of following forces, activated by the keyword TYPE_CHARGE =” SUIV “in the [STAT_NON_LINE] command. However, the choice of the current configuration as a reference configuration (updated Lagrangian) leads to simple expressions (with some notions of differential geometry) of the work of the pressure forces and of its primary variation with respect to the displacement, the latter being a non-symmetric bilinear form.