[en] The application of global methods to design reinforced concrete structures was investigated. The dynamic calculation of beam structures can be carried out very economically and with suitable accuracy by these methods. Moreover, one ideal application of global methods is design to failure, in order to estimate the safety margins of a given structure subject to accidental stresses, such as explosions, earthquakes, aircraft crash etc. In all cases, the global method combined with finite element programs serves to determine the failure automatically, and offers a good estimate of the failure load

[en] In order to predict the behaviour of composite beams and shells loaded up to failure, a global method has been developped. This method is based on a generalized stress approach, formulated in terms of moment-curvature relations. The case of a reinforced concrete slab subjected to uniform pressure has been considered. It is shown that numerical results compare fairly well with experimental data. Some improvements to the model are also suggested

[en] A series of triaxial tests has been performed on micro-concrete cylinders. The specimens have been strained with a constant displacement rate, up to a deformation of about 10%. Two different domains were distinguihed. For low confining pressures strain softening is observed, the behaviour of the material becomes ductile for high confining pressures. Continuous measurement of the volume of fluid which had to be injected or withdrawn from the cell, to keep the confining pressure constant during the test, allowed to obtain data, concerning the overall lateral deformations of the specimens. Some specimens were also subjected to successive loadings with different confining pressures, in order to study the influence of stress path

[en] The durability of structures, because of its economic and environmental implications, is one of the actual hot topics in civil engineering. In the field of nuclear energy, we are facing very challenging problems like: how could we prolong the service life of actual nuclear containments and how can we assure the durability of a radioactive storage on the very long term (several centuries)? These already difficult questions in a classical civil engineering view are even more complicated in the field of nuclear energy where the structures are massive and the safety of the installations has to be considered. For the containment of nuclear power plants, these stakes will be lit with some examples of research concerning the mechanical behaviour of concrete and concrete structures (at early age, in service on long scales of time and in the event of an accident), the durability of the concrete structures (leaching, swelling due to delayed ettringite formation - DEF -) and the couplings between mechanics and durability. Finally, the importance of probabilistic aspects and the inherent difficulties will be shown. (authors)

[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)

[en] A specific concrete model has been developed to investigate the problem of concrete walls perforation by a missile: three types of damage are accounted for: traction damage, shear damage, hydrostatic pressure damage. In order to investigate the validity of this concrete model in simple compressive conditions, tests are performed in following configuration: microconcrete used in perforation tests is cast in a cylindrical mould 100 mm diameter, 50 mm wall thickness made of very strong steel. The concrete height is 400 mm. A silver layer is put on the inner face to decrease the friction coefficient. The load is transmitted to the contrete by means of a metal piston. A quasi static test is first performed using a hydraulic testing machine. A second one is then impacted by a 32 kg mass dropping from 19 meters. In both cases the displacement and the forces are recorded for comparison with calculation

[en] In order to predict the behaviour of composite beams and shells loaded up to failure, a global method has been developped. This method is based on a generalized stress approach, formulated in terms of moment-curvature relations. The case of a reinforced concrete slab subjected to uniform pressure has been considered. It is shown that numerical results compare fairly well with experimental data, Some improvements to the model are also suggested. (orig.)

[en] Among the various reinforced concrete structures which can be subjected to seismic loadings, buildings are of main concern for safety and economical reasons. Their two main structural components are beams and shear walls. The numerical prediction of the behaviour of such structures under seismic loads requires global models. Such models are nowadays available for beams (1), but there is still much work to do for shear walls. In order to be able to derive global models for shear walls the analysis by means of refined local models can be of great help to understand and identify the major mechanisms. An experimental and theoretical program has been undertaken at CEA (FRANCE) in order to investigate the behaviour of shear walls. Some tests results which have already been presented (2) were used for comparison with numerical predictions. For this purpose, an elasto-plastic fracturing concrete model has been used. (3) Basics features like strain-softening and crack closure are of major importance for the good performance of the model in case of seismic loadings. Different calculations were performed in order to appraise the influence of various parameters like the elastic stiffness of the wall or the traction strength of the concrete. This analysis leads to some understanding of the ruin mechanisms of shear walls under seismic loadings. (author)

[en] In containment design, the behaviour of concrete is generally modelled using elastic linear laws in calculation codes based on the finite element method. When severe accidents are considered, which generally involve beyond design basis loading, the concrete can no longer be assumed to be isotropic or have an elastic linear behaviour: cracks introduce discontinuities and non-linear phenomena. The aim of this report is to present some tools developed using the CASTEM 2000 Finite Element Code and which are used to understand the behaviour of degraded concrete structures better, when considering the conjugated effects of tendons, rebars, liner and concrete cracks. This study is aimed at establishing the feasibility and the usefulness of such an approach to predict concrete structure damaging. The results are: qualitative comparison of these theoretical results with those observed on mock-ups pressurized up to failure shows similar cracks patterns; the softening of the structure due to concrete cracking is taken into account; with temperature and pressure increase the radial vertical cracks are more numerous and their widening and depth are increasing accordingly; the stress redistribution between concrete and metallic fiber (tendons, rebars) or plate with cracks is consistent with the fundaments of reinforced concrete; the liner may be compressed even if concrete is in traction: it is caused by temperature gradient

[en] The structural analysis of reinforced concrete structures is usually performed either by means of simplified methods of strength of materials type i.e., global methods, or by means of detailed methods of continuum mechanics type, i.e., local methods. For this second type, some constitutive models are available for concrete and rebars in a certain number of finite element systems. These models are often validated on simple homogeneous tests. Therefore, it is important to appraise the validity of the results when applying them to the analysis of a reinforced concrete structure, in order to be able to make correct predictions of the actual behavior, under normal and faulty conditions. For this purpose, some tests have been performed on reinforced concrete beams, subjected to monotonous and cyclic loadings, in order to generate reference solutions to be compared with the numerical predictions given by two finite element systems