Toward a model for wall-slab junctions in nuclear reinforced concrete structures: first steps

International audienceAs part of the periodic reassessments of the safety of existing nuclear structures and the design of new ones, the contribution of wall-slab junctions to both behaviour and resistance of nuclear buildings subjected to seismic loadings is investigated. An experimental program has been defined jointly with the CEA [REF], in order to improve our knowledge of the junctions' behaviour. In parallel, work is underway in order to propose a model of the junctions, starting first from literature experimental observations and numerical detailed 3D computations results. Unlike previous global models for RC junctions in the literature, whose validity domain is generally limited either to out-of-plane or to in-plane stresses, our aim is to define a model fit to be integrated in a structural FE plate or shell model of a nuclear building. The purpose of this model is to represent the contribution of the junction to both stiffness and resistance when the building is subjected to seismic loads, that can include both in-plane and out-of-plane components. The purpose of this paper is to present the first steps achieved in the definition of this model, starting from the representation of the junctions in their elastic behaviour domain. Starting from the 3D kinematics in the joint area, a model of behaviour able to represent accurately the deformation modes of the elastic joint subjected to diverse loads has been selected. It is connected to plates elements which represent the behaviour of thin structural elements (walls, floors) in order to transmit the displacements and rotations at its interfaces. The boundary between the junction element and the plate elements representing walls and floors is set at the limit of the respective structural elements, thus increasing the representativeness of these FE models. The capacity of this model to effectively represent the joint stiffness is assessed in the elastic range, first considering a homogeneous material and then taking into account the presence of both concrete and reinforcement in the structure. A parametric study is carried out, in order to validate the model within the variation range of thicknesses, reinforcement ratio, etc. representative of nuclear buildings. The results are presented herein. In a second time, the framework of the non-linear model proposed to describe the junctions' behaviour beyond their elastic range is exposed