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With the lattice element method, it is required to introduce a length via, for example, a non-local approach in order to satisfy the objectivity of the mechanical response. In spite of this, the mesoscale structuring of inclusions within a matrix conveys the natural origin of the internal length for a fixed mesh. In other words, internal length is not explicitly provided to the model, but rather governed by the characteristics of the meso-structure itself. This study examines the influence that the meso-structure of quasi-brittle materials, like concretes, have on the width of the fracture process zone and thus the fracture energy. The size of the fracture process zone is assumed to correlate with a microstructural dimension of the quasi-brittle material. If a weakness is introduced by a notch, the involvement of the ligament size (a structural parameter) is also investigated. These analyses provide recommendations and warnings that could be beneficial when extracting, from material meso-structures, a required internal length for nonlocal damage models. Among the observations made, the study suggests that the property that best characterise a meso-structure length would be the spacing between inclusions rather than the size of the inclusions themselves. It is also shown that microstructural dimension and the width of the fracture process zone have comparable order of magnitude, and they trend similarly with respect to microstructural sizes such as the inclusion interdistances.

The problem of damage in heterogeneous materials has received particular attention in recent years. The numerical models currently used in the simulation of damage require an internal length that is not currently related to a characteristic length of the material components. However, understanding damage regarding the size of the heterogeneities of the material is of crucial importance, particularly in civil engineering. The Fiber Bundle Model has been widely used to qualitatively address the issue of damage in heterogeneous media by studying the statistics of failure events during damage. The so-called ZIP model derives from Fiber Bundle Model to mimic crack propagation. In this work, a spatial correlation of tensile strength of fibers is added to the ZIP model to highlight the role of heterogeneity size in statistics of failure events during crack propagation. The addition of spatial correlation into the ZIP model modifies the distribution of failure events. Indeed, for a simulated material without spatial correlation, failure events follow two regimes. By adding a spatial correlation to the material, a transitional regime appears. The influence of spatial correlation on fiber rupture avalanche strongly depends on the ratio between the sizes of the shapes of the stress field and of the heterogeneities.

Ce chapitre introduit les étapes d’une modélisation probabiliste du comportement thermohydromécanique – variable dans l’espace – des ouvrages en béton. À titre d’exemple, la fuite d’une enceinte de confinement est modélisée sous forme d’un chaos polynomial. L’étude fiabiliste des grands ouvrages de génie civil vieillissants apparaît ainsi accessible et utile à une meilleure maîtrise des risques et opérations de maintenance et de réparation.

In the case of quasi-homogeneously applied tensile loads, the intrinsic scattering of concrete properties leads to spatially random strain localization, crack initiation and propagation. The modelling of such spatial randomness, in the case of Equivalent-Homogeneous-Material Finite Elements based approaches, can be achieved thanks to the use of Random Fields. However, when aiming at probabilistic analyses, numerous realizations are required which induces a hefty computational time and restricts their applicability to the modelling of large concrete structures. In this contribution, an original probabilistic coupling strategy is provided based on non-intrusive Stochastic Finite Elements Methods. It consists of defining an explicit Surface Response of the cracking patterns expressed in terms of the most influential inputs using an Adaptive Surface Response Method combined to a Polynomial Chaos Expansion Method. Direct Monte Carlo Method is then applied—to the explicit Surface Response of the cracking patterns—to achieve Global Sensitivity Analysis, Uncertainties Quantification and probabilistic modelling at a reasonable cost. The defined strategy is validated based on a Representative Structural Volume of a 1:3 scaled experimental Containment Building at early age using a weakly coupled thermo-mechanical model. As a result, the study quantifies the effect of the most influential parameters (the Young’s modulus—the tensile strength—the coefficients of thermal expansion and autogenous shrinkages) on concrete cracking at early age and provides accurate numerical prediction of the cracking patterns (cracks’ number, opening and spacing values) observed on site and their frequencies.

As demonstrated in Part I of this contribution, the precise and full prediction of the cracking patterns and concrete’s global behaviour in ageing structures is a complex task. Though the suggested modelling strategy allows the prediction of the main cracking patterns, its drawbacks are mainly related to (a) the use of the so-called Statistical Size Effect Law requiring various random field realizations (more than 30) and (b) the identification of a consequent number of Thermo-Hydro-Mechanical parameters (more than 50) which variations may also affect the computed cracking patterns and ageing behaviour. In part II of this contribution, the aim is to evaluate the effect of such uncertainty-related variations on concrete’s early age and long term behaviours (in comparison with the effect of the intrinsic spatial variation of mechanical properties in part I). With that regard, a 1st order sensitivity analysis to the various input’s variation is performed using the OFAT method. Throughout the study, the robustness (model’s convergence) and predictiveness (physical representativeness of numerical results) of the suggested model in Part I are evaluated within the identified inputs’ variation domains. The obtained results, in terms of the 1st order global sensitivity indexes, provide a subjectively quantitative and objectively qualitative ordering of the most influential parameters within the model’s associated physical hypotheses. In particular, the obtained results show (a) the relevance of the Gaussian function to describe the spatial correlation of the Young’s modulus property (b) the dependence of early age behaviour on, both, the spatial scattering of the mechanical properties and the maturity process; but mostly, on the structural size effect assessment (c) the main dependence of long term behaviour on the drying history and applied prestressing loads and (d) the importance of uncertainties propagation through the Thermo-Hydro-Mechanical calculations and through the operational lifespan of ageing concrete structures.

Several factors are acting on concrete dams and affect dam displacements: hydrostatic load, thermal effect and irreversible phenomena (creep, swelling …). The different influences need to be quantified for the analysis of monitoring measurements. In most statistical models for the dam behavior analysis, the thermal effect which is often the main contributor to the total displacement is introduced only by means of the dam temperatures. Recently Tatin et al. (2015) have introduced a global gradient across the dam of the temperature bringing an additional bending effect. However, the thermal gradient may be very different, even with opposite sign, from the top to the bottom depending on seasons. In this paper, a statistical model accounting for the water temperature profile is proposed. In this original statistical model, the dam is discretized along its height in n layers on which both mean and gradient of the dam temperature are computed for the evaluation of the thermal effect. It implies 2 · n new explicative variables for the statistical model yielding a reduced dispersion of the residuals. However, statistical compensation occurs from one layer to the next leading to unrealistic influence functions along the height of the dam. In order to reduce this effect, the statistical problem is constrained by imposing a polynomial approximation of influence functions. The parameters of the polynomial may be estimated either beforehand by means of the dam numerical model or directly by the statistical process. The number of additional degrees of freedom of the statistical process is thus reduced but can still describe the effects of both profiles of the water temperature and the dam thickness on dam displacements. For the model construction and validation, an arch dam is modelled by means of the finite element method and serves as a virtual case study. Although results show only a slight reduced residual dispersion, physical meaning of the model to the intermediate quantities is increased.

International audience; This article focuses on a new experimental apparatus for investigating fluid flow under high pressure gradients within low-permeability porous media by means of neutron imaging. A titanium Hassler cell which optimises neutron transparency while allowing high pressure confinement (up to 50 MPa) and injection is designed for this purpose and presented here. This contribution focuses on the development of the proposed methodology thanks to some preliminary results obtained using a new neutron imaging facility named NeXT on the D50 beamline at the Institute Laue Langevin (Grenoble). The preliminary test was conducted by injecting normal water into concrete sample prepared and saturated with heavy water to take advantage of the isotope sensitivity of neutrons. The front between these two types of water is tracked in space and time with a combination of neutron radiography and tomography.

This numerical study investigates the creeping flow of an elasto-viscoplastic fluid around a plate perpendicular to the flow direction. The analysis is performed with the Finite Element Method with Lagrangian Integration Points (FEMLIP). This numerical method is able to simulate large deformations problems and to describe yielded and unyielded regions by precisely accounting for elastic stresses. An elasto-viscoplastic model coupling the Bingham and the Maxwell constitutive equations is used. The influences of plasticity and elasticity on kinematic and stress fields are discussed. The influence of elasticity on the fore-aft asymmetry of the flow morphology is shown and quantified. The size and shape of the yielded and unyielded regions around the obstacle are also quantified. Finally, far and local stress fields as well as the drag coefficient are quantified as a function of the plastic and elastic contributions.

The forecast of large concrete structures behavior such as Nuclear Containment Buildings (NCB) is a critical safety issue, whether for the structure itself or for its surrounding environment. Over the past few decades, complex finite element models have been developed for assessing the mechanical behavior and the leak tightness of large concrete structures. These models involve numerous parameters known with uncertainties, which importance could jeopardize the reliability of forecasts. Therefore, this contribution aims to present a weakly coupled Thermo-Hydro-Mechanical-Leakage methodology to forecast the evolution of dry air tightness of large concrete structures. The proposed approach is based on a Bayesian updating strategy aiming to reduce uncertainties on forecasts by combining information provided by both a physical model and in situ observations acquired up to date. The Bayesian strategy is coupled with a scale reduction method for ensuring applicability at the scale of large structures. The methodology is applied to a 1:3 scale NCB, in order to improve confidence level of leakage rate forecasts by taking advantage of monitoring measurements. The forecasted leakage rates are in good agreement with the measurements, and the proposed methodology enables to significantly reduce the uncertainty throughout the operational phase of the structure, even with a limited amount of monitoring data.

This study focuses on the creeping flow of an elasto-viscoplastic fluid around a flat plate moving at a constant velocity. The flow is analyzed both experimentally and numerically. The experiments are performed with a Carbopol gel whose behavior is described by an elasto-viscoplastic model in the numerical analysis. This elasto-viscoplastic model is a 3D Elastic Herschel–Bulkley model implemented in a numerical tool based on the Finite Element Method with Lagrangian Integration Points (FEMLIP). In this model, the yield stress is detected by means of the second invariant of the Cauchy stress tensor and the fluid behaves elastically below the yield stress. The model relies on the understanding of the flow properties especially below the yield stress. After a presentation of the experimental protocol and the numerical method, the numerical and experimental results are compared in terms of kinematic fields and drag coefficients.

International audience; In a sheared and confined granular flow, the mean force and the force fluctuations on a rigid wall are studied by means of numerical simulations based on the discrete element method. An original periodic immersed-wall system is designed to investigate a wide range of confinement pressure and shearing velocity imposed at the top of the flow, considering different obstacle heights. The mean pressure on the wall relative to the confinement pressure is found to be a monotonic function of the boundary macroscopic inertial number which encapsulates the confinement pressure, the shearing velocity, and the thickness of the sheared layer above the wall. The one-to-one relation is slightly affected by the length of the granular system. The force fluctuations on the wall are quantified through the analysis of both the distributions of grain-wall contact forces and the autocorrelation of force time series. The distributions narrow as the boundary macroscopic inertial number decreases, moving from asymmetric log-normal shape to nearly Gaussian-type shape. That evolution of the grain-wall force distributions is accompanied at the lowest inertial numbers by the occurrence of a system memory in terms of the force transmitted to the wall, provided that the system length is not too large. Moreover, the distributions of grain-wall contact forces are unchanged when the inertial number is increased above a critical value. All those results allow to clearly identify the transitions from quasistatic to dense inertial, and from dense inertial to collisional, granular flow regimes.

This paper presents, for the first time, full-field dynamic measurements of vapour injection and condensation within a fractured concrete, observed in-operando by means of rapid neutron radiography (acquisition rate of 30 Hz with 87 μ m pixel size). Time-dependant moisture evolution is analysed in terms of equivalent water thickness measurements. We observe that movement of condensed moisture along and transversely to the crack plane is non-monotonic in both space and time, exhibiting occasional sub-second jumps.

The paper describes a proposed unified hydro-elasto-plastic model with a solid–fluid transition. The model associates a hydro-elasto-plastic model for partially saturated geomaterials, a Bingham’s viscous law, and the transition criterion between solid and fluid states. The model describes both solid and fluid behaviours of partially saturated geomaterials in a unified framework. In addition, this paper describes a novel Finite Element Method with Lagrangian Integration Points (FEMLIP) formulation for solving hydro-mechanical problems. Based on the equilibrium equation of momentum and the continuity equation of water flow, the formulation was developed and implemented in a FEMLIP tool. Bishop’s effective stress expression and proper water retention diagrams were taken into account. A heuristic column and real rainfall-induced mudflows were also simulated and analysed in this study. The permeability effects of partially saturated soil and the effective cohesion were considered, which included consideration...

International audience; This contribution aims at improving the finite element modelling of concrete's damage‐permeability coupling using continuous and elastic‐based damage approaches. With this aim in view, a review of existing local and nonlocal damage formulations is performed showing how they differ in terms of damage estimation, crack propagation, and spatial discretization restrictions (when the energy‐based Hillerborg criterion is applied). Another critical review of damage‐based permeability laws is achieved to pinpoint their limitations. Indeed, the use of a bounded and strictly increasing damage variable does not allow (1) an accurate description of permeability in the presence of macrocracks that are physically unbounded and (2) a proper description of the permeability decrease as those macrocracks are closed. Accordingly, a new strain‐based permeability law is suggested. Its analytical validation is based on the BIPEDE tensile test for one loading‐unloading cycle. This new formulation intends to enhance the predictiveness of damage‐permeability coupling models leading to a better assessment of large structure's durability and serviceability.

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International audience; The Callovo Oxfordian clay-rock (COx) is studied in France for the disposal of radioactive waste, because of its extremely low permeability. This host rock is governed by a hydromechanical coupling of high complexity.This paper presents an experimental study into the mechanisms of water uptake in small, unconfined, prismatic specimens of COx, motivated by the comprehension of cracking observed during concrete/COx interface sample preparation. Water uptake is monitored using both x-ray tomography and neutron radiography, the combination of these imaging techniques allowing material deformation and water arrival to be quantified respectively.Given the speed of water entry and crack propagation, relatively fast imaging is required: 5 minute x-ray tomographies and ten-second neutron radiographies are used. In this study, pairs of similar COx samples from the same core are tested separately with each imaging technique. Two different orientations with respect to the core are also investigated. Analysis of the resulting images yields with micro-and macro-scale insights into hydro-mechanical mechanisms to be obtained. This allows the cracking to be interpreted as a rapid breakdown in capillary suction (supposed large both to drying and rebound from in-situ stress state) due to water arrival, which in turn causes a loss of effective stress, allowing cracks to propagate with ease, which in turn deliver water further into the material.

International audience; The present paper deals with modelling the nonlinear behaviour of concrete using the fibre element method. Proved to be efficient for slender structural elements mainly subject to normal stresses, the method lacks in accuracy when modelling the effect of shear. The present contribution proposes to enhanced a Timoshenko fibre beam element by adding shear warping deformations in the formulation. Transverse shear as well as torsion warping is taken into account, enabling the computation of the response to a complex loading. Warping degrees of freedom are computed simultaneously with the beam degrees of freedom by a fully implicit solution procedure. Concrete is modelled using a 3D damage model. Due to the coupling of warping and global beam degrees of freedom, the warping displacements in the beam element can evolve with the evolution of concrete damage. The beam element enhancement is validated at the cross-section scale considering a linear elastic behaviour. Enhanced beam elements are then used to model experimentally-tested structural elements. Both the linear and non-linear parts of the structural response are investigated.

The prediction of large concrete structures behavior such as bridges, dams and Nuclear Containment Buildings (NCB) is a key issue with regards to the evaluation of their durability, safety and the safety of their surrounding environment. In this work, a weakly coupled Thermo-Hydro-Mechanical (THM) modeling strategy is presented within the serviceability state of large structures. It aims at (a) defining and predicting the temperature, the relative humidity, the strains and the stresses in ageing concrete structures under variable and realistic THM loads and (b) qualitatively assessing the damage risk using a stress-based criterion. With that aim in view, the effect of concrete drying on its long term behavior is highlighted by using a revisited description of drying creep adapted to variable hydric conditions. The concrete’s response to variable THM boundaries is also compared to the one where mean and constant ones are considered in the case of NCBs. Two concrete types and three scales are considered for the THM study: the specimen scale for concrete properties identification, the 1:3 and 1:1 (full) scales of Representative Structural Volumes (RSV) for predictive and structural analyses. Through the FE sensitivity analysis, it is shown that the spatial variation of the temperature along the NCB’s height has more effect on the concrete’s ageing than its variation in time. Whereas, the temporal variation of hydric boundaries has a negligible effect away from the drying-exposed surfaces. Finally, it is demonstrated that, due to initial prestressing loads, the ageing kinetic within the NCB’s wall is heterogeneous and cannot be described using constant prestressing loads. Therefore, it is recommended to account for the spatial THM boundaries’ variation when predicting the global concrete ageing in large concrete structures.

The delayed mechanical behaviour of the clay-rock/concrete interface under shear stress has been experimentally investigated. After a first characterisation of the short-term response of the interface with direct shear tests, long duration shear tests under constant normal load have been performed with a new experimental apparatus which was developed for this study. The response of the interface in time is discussed.

In the case of homogeneously distributed stress loads, the intrinsically random distribution of voids and defaults in the concrete volume is one of the driving factors of strain localization, crack initiation and propagation. In this contribution, a macroscopic approach based on a stochastic and continuous damage model is suggested to describe concrete’s cracking under simultaneous Thermo-Hydro-Mechanical (THM) loads. Statistical and energetic size effects at the structural scale are taken into account by (a) reducing the mean tensile strength of the considered concrete’s effective volume according to a probabilistic-based Size Effect Law (SEL) adapted to local models, (b) performing an energy-based regularization for mesh independency and (c) describing the spatial distribution of the Young’s modulus property using autocorrelated lognormal Random Fields (RF). The proposed strategy is applied to the first lift of the VeRCoRs Nuclear Containment Building mock-up (the gusset) which undergoes, at early age, restrained endogenous and thermal shrinkages and, during the Operational Phase (OP), several pressurization tests leading to possible concrete cracking and damage increase. Different cracking patterns are predicted and their evolution in time due to the concrete’s ageing phenomena is analyzed. The predicted numerical results (i.e. temperature, strains and cracking patterns) are in line with in situ observations and support the need for statistical description of concrete cracking rather than classical deterministic analyses.

International audience; The term “spatial variability of seismic ground motions” denotes the differences in the amplitude and phase content of seismic motions. The effect of such spatial variability on the structural response is still an open issue. In-situ experiments may be helpful in order to answer the questions regarding both the quantification of the spatial variability of the ground motion within the dimensions of a structure as well as the effect on its dynamic response. The goal of the present study is to quantify the variability of the seismic ground motion accelerations in the shallow sedimentary basin of Argostoli, Greece, and thereafter to identify its effect on the linear and non-linear elasto-plastic response of a single degree of freedom system in terms of spectral displacements. Around 400 earthquakes are used, recorded by the 21-element very dense seismological array deployed in Argostoli with inter-station spacing ranging from 5 to 160 meters. The seismic motion variability, evaluated in terms of spectral accelerations, is found to be significant and to increase with inter-station distance and frequency. Thereafter, the amplitude variability in terms of spectral displacements, which is indeed the linear response of a single degree of freedom (SDOF) system with various fundamental periods, is compared with the amplitude variability of a SDOF with non-linear elasto-plastic response. The variability of the maximum top displacement of the linear single degree of freedom system is estimated to be on average 12% with larger variabilities to be observed within two narrow frequency ranges (between 1.5 and 1.7 Hz and between 3 and 4 Hz). Such high variabilities are caused by locally edge-generated diffracted surface waves. The non-linear perfectly elasto-platic structural response of the SDOF system shows that although the variability has the same trends as in the case of linear response, it is almost constantly increased by 5%.

Discrete element simulations are used to model a two-dimensional gravity-free granular sample, which is trapped between two smooth sidewalls and one bottom rough wall while being subject to a constant shearing velocity at the top under a given confinement pressure. This system, inspired by conventional fluid mechanics, is called a granular lid-driven cavity. Attention is firstly paid to the time-averaged dynamics of the grains once a steady-state is reached. Strong spatial heterogeneities associated with a large-scale vortex formed within the whole volume of the lid-driven cavity are observed. The mean steady force on the sidewall facing the shearing velocity is then investigated in detail for different cavity lengths, shearing velocities and confinement pressures at the top. The ratio of the force on the latter wall to the top confinement pressure force is not constant but depends on both the shearing velocity and the confinement pressure. Above a critical value of the cavity length relative to the wall height and over a wide range of both shearing velocity and top confinement pressure, all data merge into a one-to-one relation between the mean force scaled by the top pressure force and the macroscopic inertial number of the lid-driven cavity. This result reveals the key role played by the inertial rheology of the granular material in the granular force transmission.

Relative average-spectral-acceleration (ASA40), a recently developed intensity measure, is defined as the average spectral pseudo-acceleration on the probable interval of evolution of the fundamental frequency of a structure. This article presents two ground motion prediction equations (GMPEs) appropriate for the prediction of ASA40, using a pan-European strong motion database. Taking advantage of the strong correlation between the new intensity measure ASA40 and the spectral pseudo-acceleration (SA), existing GMPEs predicting SA can be adapted to predict ASA40. The first GMPE used in this study is the modified version of a new generation ground motion model, ASB13. In order to decrease the high aleatory uncertainty (sigma) that accompanies predictions when using this modified model, a new model is developed for the prediction of ASA40. Its range of applicability is for magnitudes Mw from 5.5 to 7.6 and distances out to 200 km, it includes site amplification and it is applicable for a range of periods between 0.01 and 4 s. The proposed model decreases the aleatory uncertainty by almost 15 % with respect to the uncertainty of the modified ground motion model.

Summary A fundamental issue in the framework of seismic probabilistic risk analysis is the choice of ground motion intensity measures (IMs). Based on the floor response spectrum method, the present contribution focuses on the ability of IMs to predict non-structural components (NSCs) horizontal acceleration demand. A large panel of IMs is examined and a new IM, namely equipment relative average spectral acceleration (E-ASAR), is proposed for the purpose of NSCs acceleration demand prediction. The IMs efficiency and sufficiency comparisons are based on (i) the use of a large dataset of recorded earthquake ground motions; (ii) numerical analyses performed on three-dimensional numerical models, representing actual structural wall and frame buildings; and (iii) systematic statistical analysis of the results. From the comparative study, the herein introduced E-ASAR shows high efficiency with respect to the estimation of maximum floor response spectra ordinates. Such efficiency is particularly remarkable in the case of structural wall buildings. Besides, the sufficiency and the simple formulation allowing the use of existing ground motion prediction models make the E-ASAR a promising IMs for seismic probabilistic risk assessment. Copyright © 2015 John Wiley & Sons, Ltd.

International audience; The force fluctuations experienced by a boundary wall subjected to a lid-driven cavity flow are investigated by means of numerical simulations based on the discrete element method. The time-averaged dynamics inside the cavity volume and the resulting steady force on the wall are governed by the boundary macroscopic inertial number, the latter being derived from the shearing velocity and the confinement pressure imposed at the top. The force fluctuations are quantified through measuring both the autocorrelation of force time-series and the distributions of grain-wall forces, at distinct spatial scales from particle-scale to wall-scale. A key result is that the grain-wall force distributions are entirely driven by the boundary macroscopic inertial number, whatever the spatial scale considered. In particular, when the wall-scale is considered, the distributions are found to evolve from nearly exponential to nearly Gaussian distributions by decreasing the macroscopic inertial number. The transition from quasistatic to dense inertial flow is well identified through remarkable changes in the shapes of the distributions of grain-wall forces, accompagnied by a loss of system memory in terms of the mesoscale force transmitted toward the wall.

A new experimental apparatus is presented for testing the time-dependent behaviour of interfaces, including in particular interfaces of geomaterials, under constant loading. This apparatus allows the application of two orthogonal loads normal and tangential to the mean plane of the interface, as well as the measurement of the axial and tangential relative displacements. The sample is moulded inside two half shear boxes and the system is designed in such a way that the shear force is applied along the mean plane of the interface. Some preliminary testing was carried out on a clay rock/concrete interface, under a controlled temperature environment. Preliminary results are presented, showing the evolution of the delayed displacements.

The goal of the present study is to quantify the spatial variability of seismic ground motions (SVGM) at the arch dam–foundation rock interface, using data coming from a case study, and the effect of the presence of the structure and the local topography on it. For this purpose, a dense seismological network, consisting of 19 velocimeters, was deployed during 1 year in the Saint Guerin arch dam in France. Fifty-five recorded events are used for the analysis. Both amplitude (in terms of differences of Fourier amplitudes) and phase variability (in terms of lagged coherency) are evaluated at the dam–foundation rock interface and in the free-field. Two lagged coherency models, Menke et al. (Bull Seismol Soc Am 80:430–449, 1990) and Ancheta et al. (Proceedings of 4th IASPEI/IAEE international symposium on effects of surface geology on seismic motion, Aug 23–26, 2011) amplitude variability model are compared with the observations in Saint Guerin and the overall fit is satisfactory. The comparison with the free field motions and the existing models imply that local topography at the interface does not contribute to a significant increase of SVGM. However, higher phase and amplitude variability is observed around the frequencies of vibration of the structure. The numerical model of the dam and a simple representation of the surrounding site confirm the in situ observations.

A fundamental issue that arises in the framework of probabilistic seismic risk analysis is the choice of ground motion intensity measures (IMs). A new structure-specific IM, namely, relative averag...

SUMMARY Given the contrasting behaviour observed for geomaterials, for example, during landslides of the flow type, this contribution proposes an original constitutive model, which associates both an elasto-plastic relation and a Bingham viscous law linked by a mechanical transition criterion. This last is defined as the second-order work sign for each material point, which is a general criterion for divergence instabilities. Finite element method with Lagrangian integration points is chosen as a framework for implementing the new model because of its well-known ability to deal with both solid and fluid behaviours in large deformation processes. A first boundary model considering a sample of initially stable soil, a slope and an obstacle is performed. The results show the power of the constitutive model because the consistent evolution of initiation, propagation and arrest of the mudflow is described. A parametric study is led on various plastic and viscous parameters to determine their influence on the flow development and arrest. Finally, forces against the obstacle are compared with good agreement with those of other authors for the same geometry and a pure viscous behaviour. Copyright © 2014 John Wiley & Sons, Ltd.

The shear behaviour of bonded concrete-granite joints under constant normal stress conditions is experimentally investigated in this paper. Concrete was prepared following standard mix used in pre-existing dams in France and poured on granite samples with a natural surface roughness. Before the direct shear tests, the joint surfaces were scanned by a laser profilometer to obtain the 3D morphology features. By analysing the shear test results, no direct correlations were found between the shear strength of bonded joints and classical roughness parameter.

An experimental campaign is carried out to study the effect of drying shrinkage and temperature on multi-directional gas permeability of dry concrete. Thermal loadings up to 250°C are applied on concrete samples in cylinder (11×22) and dog-bone forms (total length of 61 cm). Samples are sliced for permeability measurements. Permeabilities in longitudinal and radial directions are addressed. The cylinder samples are first sliced then dried or heated whilst the dog-bone samples are first dried or heated then sliced. The average of initial intrinsic permeability for the slices (5 cm height, 11 cm diameter) obtained from the (11×22) samples is found isotropic and equal to 2.93×10-17 m2. In this case, drying shrinkage is isotropic. Furthermore, it is shown that for the dog-bone samples, drying shrinkage may induce micro-cracks preferentially in a certain direction which induces permeability anisotropy. Finally, the evolution of the normalized intrinsic permeability with respect to initial permeability versus temperature is found isotropic. An exponential fitting of intrinsic permeability versus temperature is found based on experimental measurements.

International audience; This paper introduces a new approach for FE modelling of 1D steel inclusions within a 3D concrete domain. Reinforcements modelled with 1D meshes, when included in 3D domains, are indeed responsible for pathological effects like stress concentration at the local scale. The alternative solution of an explicit 3D mesh of the steel elements requires a large amount of work, and a relatively fine conform mesh (and therefore, additional computation cost). It is thus hardly applicable to large-scale structures. The approach proposed in this contribution, called “1D-3D”, generates an equivalent volume from a 1D mesh of the reinforcements. Associated stresses and stiffnesses, which can be condensed on the boundaries of the newly created volume, are then applied to concrete 3D elements using kinematic relations. This approach is validated on two representative cases of civil engineering applications, including active and passive steel reinforcements. It provides results similar to an explicit 3D approach, without its meshing complexity. It thus combines the advantages of 1D and 3D approaches in a single modelling.

This paper deals with a new model for solving coupled hydromechanical problems, based on an existing unified model. Firstly, the unified model for granular media, describing solid and fluid states with the transition between them, is briefly presented and extended to the unsaturated domain using Bishop’s effective stress. Secondly, an adapted stress–strain relationship is derived from modified Van Genuchten–Mualem’s water retention curves. On this basis, a finite element formulation with Lagrangian integration points in a visco-elasto-plastic framework is proposed and implemented in a FEMLIP tool. Finally, the formulation is validated with reference to several benchmarks. The results and analysis show its reliability, and by means of FEMLIP, more complex and realistic problems are expected to be solved in the field of natural risks.

International audience; This paper introduces a coupled approach between stochastic finite element methods and an adaptive condensation technique for the analysis of nonlinear mechanical problems under uncertainties. This coupling reduces the size of each individual nonlinear problem solved in SFE by the use of an adaptive condensation method. The reduced stiffnesses and other quantities necessary for the condensation technique are approximated using a second, low-order, polynomial expansion, thus taking advantage of the coupling with SFE. This approach also features a semi-analytical technique to compute accurately distributions of structural quantities of interest. This method is applied on an elasto-plastic steel bar with a small defect, and on a damaged beam under 4-point bending. In both cases it predicts the random behavior of the structure quite accurately, and is able to provide higher-order models than a state-of-the-art stochastic collocation method, for a reduced computation time.

International audience; This contribution presents an original approach to improve the modeling of steel rebars and prestressing tendons in concrete structures at a reduced cost. Classical 1D meshes and models typically used for civil engineering applications tend to provoke strain localization due to the geometrical singularity and are thus unable to reproduce local mechanical effects. Complete 3D models can be applied in some cases, however their accuracy at the local scale comes at the cost of engineering work on the meshes, especially for complex structures. The 1D-3D model presented in this contribution generates an equivalent volume for the steel bars, based on existing 1D models. Its 3D stiffness and stress state are computed, and then condensed on its interface with the concrete. The condensed degree of freedom are then linked to the surrounding concrete elements by kinematic relations. The presented approach is validated on different representative cases, and is able to predict the 3D effects of the bars and tendons at the local scale. In particular it provides the representativeness and mesh stability of a full 3D model, without the need for a complex mesh.