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The main aim of this paper is studied the punching shear and behavior of reinforced concrete slabs exposed to fires, the possibility of punching shear failure occurred as a result of the fires and their inability to withstand the loads. Simulation by finite element analysis is made to predict the type of failure, distribution temperature through the thickness of the slabs, deformation and punching strength. Nonlinear finite element transient thermal-structural analysis at fire conditions are analyzed by ANSYS package. The validity of the modeling is performed for the mechanical and thermal properties of materials from earlier works from literature to decrease the uncertainties in data used in the analysis. A parametric study was adopted in this study, it has many factors such as the ratios of length to thickness, fire temperature, time exposed to fire, concrete compressive strength, area exposed to fires and type of support. It can be concluded from this research the significant factors that affect the punching shear strength. However, the increasing ratio of length to thickness may be lead to increasing the deflection more than 123% at fire condition. Also, the increasing temperature leads to increasing the deflection about 40% at fire condition.

A creep test performed on a Landes salt sample during one year and a half is described. During the first year, a 0.6 MPa axial load is applied to the sample. At the end of this one-year phase, strain rate ( 9 × 10 − 12 s - 1 ) is much faster than the strain rate extrapolated from high-stress tests. Steady state strain rate is not reached. In an attempt to reach steady state strain rate “from below”, a 0.9 MPa load is applied during two days before restoring the initial load (0.6 MPa). After the load is restored, reverse creep is observed first (strain rate sign changes before vanishing to zero after a few hours). Then, strain rate increases to reach 5 × 10 − 12 s - 1 after five months, slower than the strain rate before the load change. Commonly accepted constitutive laws can explain this effect, which provides a lower and an upper bound for steady state strain rate. This note presents a method to determine such bounds.

Juvenile bone growth is well described (physiological and anatomical) but there are still lacks of knowledge on intrinsic material properties. Our group has already published, on different samples, several studies on the assessment of intrinsic material properties of juvenile bone compared to material properties of adult bone. The purpose of this study was finally to combine different experimental modalities available (ultrasonic measurement, micro-Computed Tomography analysis, mechanical compression tests and biochemical measurements) applied on small cubic bone samples in order to gain insight into the multiparametric evaluation of bone quality. Differences were found between juvenile and adult groups in term of architectural parameters (Porosity Separation), Tissue Mineral Density (TMD), diagonal stiffness coefficients (C33, C44, C55, C66) and ratio between immature and mature cross-links (CX). Diagonal stiffness coefficients are more representative of the microstructural and biochemical parameters of child bone than of adult bone. We also found that compression modulus E was highly correlated with several microstructure parameters and CX in children group while it was not at all correlated in the adult group. Similar results were found for the CX which was linked to several microstructure parameters (TMD and E) only in the juvenile group. To our knowledge, this is the first time that, on a same sample, ultrasonic measurements have been combined with the assessment of mechanical and biochemical properties. It appears that ultrasonic measurements can provide relevant indicators of child bone quality (microstructural and biochemical parameters) which is promising for clinical application since, B-mode ultrasound is the preferred first-line modality over other more constraining imaging modalities (radiation, parent–child accessibility and access to the patient's bed) for pediatric patients.

During usual dental restoration procedures, the mouth and so the dental tissues are under humidity and temperature conditions that may affect the bonding efficiency, especially on dentin (Goodis et...

The applied deviatoric stress during most creep tests performed on salt samples is in the 3.5–20 MPa range. However, the stresses actually experienced in the vicinity of a salt cavern are much smaller. Any extrapolation is difficult to vindicate, as the dominant micro-mechanisms are strongly suspected to be very different in the low-stress and medium-stress domains. To answer this concern, a very slow creep test was performed on an Avery Island salt sample. To minimize the influence of even the smallest of temperature deviations during the test, the testing apparatus was placed in a remote gallery of the Varangeville salt mine, taking advantage of the very stable temperature conditions offered in an underground environment. The test was performed in multiple stages and lasted 42 months. The successive loads of 0.1, 0.2, 0.3, and 0.5 MPa were applied. Measured steady-state strain rates were of the order of 10−12 s−1, which are significantly faster than that extrapolated from creep tests performed at loads ranging between 3.5 and 20 MPa.

International audience; The mechanical behaviour of the argillaceous rock considered in France as a potential host rock for nuclear waste repository strongly depends on water content. In order to quantify the dependence of the mechanical properties on humidity, an experimental setup that combines hydromechanical loadings with optical observations and digital image correlation (DIC) has been developed. It allows investigation of the hydromechanical behaviour of a material from the sample scale (cm) down to micrometric scale (100 mu m). Using this system, the shrinkage and swelling properties of the argillaceous rock at various constant uniaxial stresses, and the linear mechanical behaviour of the material at different moisture levels, were experimentally studied. A quasi-linear relation between the relative humidity, ranging from 39% to 85%, and the deformation during dehydration and rehydration is found at both the sample scale (cm), and a mesoscopic scale of a few hundred micrometres. This relation depends on the applied stress with much less swelling at higher axial compressive stress. In addition, a linear decrease of the axial Young's modulus (normal to bedding plane) with an increase of the relative humidity is observed. (C) 2012 Elsevier Ltd. All rights reserved.

International audience; The implementation of the experimental methodology by optical measurements of mechanical fields, the development of a test bench, the specimen preparation, the experimental measurements, and the digital image correlation (DIC) method, have already been the object of research in the context of biological materials. Nevertheless, in the framework of the experimental identification of a mesoscopic stochastic model of the random apparent elasticity field, measurements of one specimen is required at both the macroscopic scale and the mesoscopic scale under one single loading. The nature of the cortical bone induces some difficulties, as no single speckled pattern technique is available for simultaneously obtaining the displacement at the macroscopic scale and at the mesoscopic scale. In this paper, we present a multiscale experimental methodology based on (i) an experimental protocol for one specimen of a cortical bone, (ii) its measuring bench, (iii) optical field measurements by DIC method, (iv) the experimental results, and (v) the multiscale experimental identification by solving a statistical inverse problem.

Hydromechanical behavior of argillaceous rocks is currently studied in order to predict the perturbations around ventilated galleries of a nuclear waste storage. This paper presents the results of desaturation–resaturation experiments performed on mudstone samples bored at 500 m depth at Bure (France) where an underground research laboratory is under construction. We characterize the mass transfer process in the Bure mudstone, in terms of moisture diffusivity as a function of the relative humidity. A diffusivity identification method based on the measured mass evolution during transfer is proposed for the cases of uniaxial and radial diffusions. A significant non-linearity of moisture diffusivity has been observed. The retention curve, the diffusivity evolution, the ultrasonic velocity and the hydric strains have been investigated during the desaturation–resaturation process without mechanical loading. Hydric strains are anisotropic and non-linear with respect to relative humidity. A hysteresis has been observed on the ultrasonic velocity evolution, on the hydric strain variation and on the retention curve. Moisture diffusivity evolution is not the same along the desaturation path than along the resaturation path; this could be explained by the difference in moisture capacity on these two paths. The effect of desaturation–resaturation on mechanical behavior of the Bure mudstone is analysed by carrying out uniaxial compressive tests on samples with different water contents. Elastic parameters and compressive strength depend clearly on the suction. The mechanical behavior seems to be sensitive to the hydric path but further testing is needed to confirm these preliminary results.

International audience; This paper deals with a multiscale statistical inverse method for performing the experimental identification of the elastic properties of materials at macroscale and at mesoscale within the framework of a heterogeneous microstructure which is modeled by a random elastic media. New methods are required for carrying out such multiscale identification using experimental measurements of the displacement fields carried out at macroscale and at mesoscale with only a single specimen submitted to a given external load at macroscale. In this paper, for a heterogeneous microstructure, a new identification method is presented and formulated within the framework of the three-dimensional linear elasticity. It permits the identification of the effective elasticity tensor at macroscale, and the identification of the tensor-valued random field, which models the apparent elasticity field at mesoscale. A validation is presented first with simulated experiments using a numerical model based on the hypothesis of 2D-plane stresses. Then, we present the results given by the proposed identification procedure for experimental measurements obtained by digital image correlation (DIC) on cortical bone.

Langer (1984) stated that reliable extrapolation of the creep equations at low deformation rates can be carried out only on the basis of deformation mechanisms. The micromechanisms that govern salt1 INTRODUCTION1.1 Norton-Hoff lawThe mechanical behavior of salt has given rise to abundant literature. When a constant mechanical load is applied to a salt sample, most authors observe: a steady-state strain rate is reached after some time, it is a nonlinear function of the applied stress, it is sensitive to temperature, and no volume change is observed. The main features of such a steady-state behavior are captured by the NortonHoff law, or d dt Ass ne σp .( )Tσ , ( )Q RT Typical values for the constants n and Q/R range from 3 to 6 and from 3,000 to 10,000 K, respectively. The steady-state strain rate d dte( ) is typically bout 10−10 s−1 for a deviatoric stress ( )σ of 10 MPa and temperature (T) of 300 K. This rate is relatively slow, and during most laboratory tests, the applied stress is larger than 10 MPa.

International audience; Digital image correlation techniques (DIC) are applied to sequences of optical images of argillaceous rock samples submitted to uniaxial compression at various saturation states at both the global centimetric scale of the samples and the local scale of their composite microstructure, made of a water-sensitive clay matrix and other mineral inclusions with a typical size of 50 μm. Various scales of heterogeneities are revealed by the optical technique. Not only is it confirmed that the clay matrix deforms much more than the other mineral inclusions, but it also appears that the deformation is very inhomogeneous in the matrix, with some areas almost not deformed, while others exhibit deformation twice the average overall strain (for a gauge length of 45 μm), depending on the local distribution of the inclusions. In almost-saturated rocks, overall heterogeneities are also linked to the presence of a network of cracks, induced by the preliminary hydric load. On such wet samples, DIC analysis shows that the overall strain results both from the bulk deformation of the sound rock, with deformation levels similar to those in dry samples, and the closing or opening of these mesoscopic cracks.

International audience; In addition to direct mechanical perturbations, an excavation influences rock conditions (mechanical, hydraulic and chemical properties). The internal fluids could be drastically modified and, in particular, the presence of water in the rock with regard to hydration and desiccation. The aim of the present study is to investigate the influence between the degree of saturation and the physical/mechanical properties for Tournemire shale rock. Anisotropy effects are also studied to identify hydromechanical behaviour. The different degrees of saturation are imposed by controlled suctions with continuous measurement of physical parameters such as weight and deformations. The volume variations (swelling or shrinkage behaviour) would result principally from the opening or closing of the inter-layers space. Uniaxial and triaxial compressive tests are carried out in order to attempt to establish a relationship between different mechanical parameters (elastic and failure data) and the sample saturation. The mechanical behaviour is sensitive to the saturation state of the shale with an important part of the stratification and its relative orientation to the mechanical stress.

International audience; Long-term creep tests have been performed on rock-salt and argillite samples under very small uniaxial loadings (σ = 0.02 to 0.1 MPa) . To minimize the effects of temperature variations, testing devices were set in a mine where temperature fluctuations are of the order of one-hundredth of a degree Celsius. The mechanical loading was provided by dead weights. The deformations were measured through special displacement sensors with a resolution of ∆ε = 10-8. Strain rates as small as έ = 7 × 10-13s-1 were measured. These tests allow rock-sample creep to be investigated at very small strain rates. The tests also prove that extrapolation of constitutive laws at very small rates is often incorrect.