Fracture of Zircaloy-4 cladding tubes with or without hydride blisters in uniaxial to plane strain conditions with standard and optimized expansion due to compression tests

International audienceTwo optimizations of the Expansion Due to Compression (EDC) test, which induces a near uniaxial loading, were proposed and developed to reach higher biaxiality ratios (ratio between mechanical quantities in axial and in circumferential direction). The first optimization, named HB-EDC for High-Biaxiality EDC, allowed to reach transverse plane strain conditions. The second optimization, named VHB-EDC for Very High Biaxiality EDC, was designed to reach higher loading biaxiality ratios. These optimized EDC tests were performed at 25 °C, 350 °C and 480 °C on unirradiated hydrided Cold Worked Stress Relieved (CWSR) Zircaloy-4 samples. First, samples unhydrided or uniformly hydrided up to 1130 wppm were tested. Second, samples hydrided at 310 wppm with a hydride blister were tested. A large ductility reduction is induced by the increase in biaxiality level in the absence of a hydride blister or with small blisters (View the MathML source<50μm deep). The fracture strain decreases quickly with the blister depth at 25 °C, but more progressively at higher temperature. An equation that quantifies the fracture strain reduction with the blister depth is proposed. Eventually, one of the tests developed in the present study, the HB-EDC test, was proven to be a good compromise between the test complexity and the stress state reached. It is a good candidate to characterize the mechanical behaviour of irradiated cladding

Full-Scale Shaking Table Tests on a Substandard RC Building Repaired and Strengthened with Post-Tensioned Metal Straps

The effectiveness of a novel Post-Tensioned Metal Strapping (PTMS) technique at enhancing the seismic behaviour of a substandard RC building was investigated through full-scale shake-table tests during the EU-funded project BANDIT. The building had inadequate reinforcement detailing in columns and joints to replicate old construction practices. After the bare building was initially damaged significantly, it was repaired and strengthened with PTMS to perform additional seismic tests. The PTMS technique improved considerably the seismic performance of the tested building. Whilst the bare building experienced critical damage at an earthquake of PGA=0.15g, the PTMS-strengthened building sustained a PGA=0.35g earthquake without compromising stability

Mechanical cyclic behaviour of 316L welded joint

To take into account the reduced fatigue strength of welded joints, a reduction factor on the fatigue curves was introduced into the RCC-MR French nuclear design and construction code. To better assess this factor, a previous work on large plates showed that the mechanical behaviour of a welded assembly is influenced by the geometry of the weld and by the interaction of the different cyclic plastic behaviour of the two materials: base metal (BM) and weld metal (WM). A new program was performed consisting in tests on butt welded pipe connections (4 points bending), fatigue tests on uniaxial specimens (uniaxial tensile-compressive load) and finite elements calculations. The uniaxial fatigue tests have been carried out on specimens extracted form a butt welded pipe connection manly at 600 °C. Some tests have been carried out at ambient temperature and have permit to realise some ESPI measurements to have a better knowledge of the strain gradients at some stage of the fatigue tests. But the use of ESPI sensor requires some experimental conditions which are hardly adaptable to real fatigue test conditions. Nevertheless, by using concurrently some classic extensometers sensors, new observations can be done on the fatigue specimens behaviour

Low cycle fatigue of welded joints : new experimental approach

International audienceTo take into account the reduced fatigue strength of welded joints, a reduction life factor applied on fatigue curves (Jf value) was introduced into the RCC-MR [Design and Construction Rules for Mechanical Components of FBR Nuclear Islands, AFCEN, 1993], for the design and construction of fast breeder reactors. To better assess this factor, previous work showed that mechanical behavior of a welded assembly is influenced by the geometry of the weld and by the interaction of the different cyclic plastic behavior of the two materials: base metal (BM) and weld metal (WM). A new procedure (named FFAST) was performed on welded joint specimens extracted from butt-welded pipe connections (uniaxial tensile–compressive load). An innovative experimental approach is proposed to study the local mechanical behavior of the welded joint specimens and then determine the Jf parameter. The main advantage of the method is to avoid problems due to the relative stiffness of weld part versus the BM part of the specimen. A continuous recording of the stress and strain in the weld allows an estimation of the mechanical behavior and finally the fatigue life of the joint. Observations of the crack surface show two different crack initiation zones near the weld depending on the load level. Calculations of the tests and comparison with experimental results are presented. These studies make it possible to assess in a practical way the Jf design method. It appears that Jf value cannot be considered as a single value for it is influenced by several factors depending on the weldment and on the load level

Nonlinear finite element analysis of unanchored steel liquid storage tanks subjected to seismic loadings

Steel liquid storage tanks are widely used in industries and nuclear power plants. Damage in tanks may cause a loss of containment, which could result in serious economic and environmental consequences. For the purpose of the earthquake-resistant design of tanks, it is important to use a rational and reliable nonlinear dynamic analysis procedure. The analysis procedure should be capable of evaluating not only the comprehensive seismic responses but also the damage states of tank components under artificial or real earthquakes. The present paper deals with the nonlinear finite element modeling of steel liquid storage tanks subjected to seismic loadings. A reduce-scale unanchored steel liquid storage tank with the broad configuration from a shaking stable test (i.e., the INDUSE-2-safety project) is selected for this study. The fluidstructure interaction problem of the tank-liquid system is analyzed using the Abaqus software with an explicit time integration approach. In particular, the steel tank is modeled based on a Lagrangian formulation, while an Arbitrary Lagrangian-Eulerian adaptive mesh is used in the liquid domain to permit large deformations of the free surface sloshing. The finite element results in terms of the sloshing of the liquid free surface and the uplift response of the base plate are evaluated and compared with the experimental data that is obtained from the shaking table test for the tank under the INDUSE-2-safety project

Assessment of the seismic behaviour of corroded RC beams: an experimental contribution

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EXPERIMENTAL STUDY OF THE SEISMIC BEHAVIOR OF CORRODED RC BEAMS

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Étude expérimentale de l'effet de la corrosion sur le comportement dynamique de poutres en béton armé

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Assessment of the seismic behavior of reinforced concrete elements affected by corrosion: An objective comparison between quasi-static and dynamic tests

International audienceCorrosion of steel reinforcement is one of the most widespread pathologies that leads to a loss of structural performance of reinforced concrete (RC) members. Thus, understanding the mechanical consequences of this pathology is of great importance. In the past decades, many studies have been performed to assess the influence of the reinforcement corrosion on the quasi-static behavior of RC structures. However, few investigations have been carried out to characterize the corroded structural dynamic behavior under extreme loading. In this study, the case of the earthquake loading is investigated. The objective is to provide the scientific community with reference experimental data to assess the influence of corrosion on the dynamic properties of structural members. These experimental data are very valuable when calibrating numerical models aiming to determine some significant engineering demand parameters (EDP) such as the bearing capacity, the ductility and the dissipation ability. Furthermore, the relevance of the use of quasi-static tests in predicting the seismic behavior of corroded RC elements is assessed. To reach this goal, an experimental campaign is conducted on large-scale RC beams. The corroded and non-corroded beams are subjected to a four-point bending test and to dynamic loads on the AZALEE shaking table (keeping the same loadings and boundary conditions). In this paper, a detailed description of the experimental campaign is presented. Then, the results are exposed, showing the influence of the corrosion rate on the bearing capacity, hysteretic response, ductility offer, eigenfrequencies and damping ratios

Effect of steel reinforcement corrosion on the dynamic behavior of RC beams

International audienceCorrosion is one of the most common pathologies that affects reinforced concrete structures (RC). The fact that this phenomenon leads to a progressive loss of structural performance does not need further discussions. This loss of performance is a crucial issue for safety, especially when considering the coupling with an external loading such as an earthquake. The present study aims to quantify the time evolution of some quantities of interest, such as the eigenfrequencies, the modeshapes or the damping ratios, as functions of the corrosion degree. To reach this objective an extensive experi-mental campaign has been set up on simple but large-scale RC specimens. The consequences of the corrosion phenomenon on both the static and dynamic behaviors of beams are quantified, considering several steel configurations. In this paper, the experimental campaign is described. Especially, the accelerated corrosion method used is presented as well as the planned loading. The paper ends with a brief description of a simplified model which is under development. Due to its low computational demand, it will be able to be used within the framework of probability safety assessment (PSA) studie