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Electrical resistivity is sensitive to various properties of concrete, such as water content. Usually used on the surface of old structures, devices for measuring such properties could also be adapted in order to be embedded inside the constitutive concrete of the linings of new tunnels or in new bridges, to contribute to structural health monitoring. This paper introduces a novel multi-electrode embedded sensor for monitoring the resistivity profile over depth in order to quantify concrete durability. The paper focuses on the design of the sensor as a printed circuit board (PCB), which brings several advantages, including geometric accuracy and mitigation of wiring issues, thus reducing invasiveness. The study also presents the numerical modeling of the sensor electrical response and its ability to assess an imposed resistivity profile, together with experimental validations using (i) saline solutions of known conductivity and (ii) concrete specimens subjected to drying. The results demonstrate the capability of the sensor to evaluate resistivity profiles in concrete with centimeter resolution.

International audience; no abstract

International audience; In civil engineering, ground-penetrating radar is widely used for road pavement survey. In contrast to the existing literature, this paper takes account of the influence of interface roughness (surface and interlayer roughness) within the scope of the data processing of radar signals. The rigorous electromagnetic method PILE (propagation inside layer expansion) provides the simulated data that show the influence of the interface roughness on the backscattered primary echoes of stratified media, the interface roughness provides a continuous frequency decay of the magnitude of the echoes. The observed frequency variations of the radar magnitude introduce some shape distortion on the radar waveform. The latter variations can be modelled by exponential function, which provides satisfactory results for a narrow bandwidth (2 GHz). An adaptation of the root-MUSIC algorithm is proposed. As a result, it is allowed to jointly estimate the time delay and the interface roughness. Then, the algorithm is tested on the data simulated by the PILE method, and numerical examples are provided to assess the performance of this algorithm. The associated results show that the proposed algorithm can estimate both the time delay and roughness parameters with a small relative error.

A ground-penetrating radar (GPR) has been developed for civil engineering applications. Ultra-wide band (UWB) bowtie slot antennas operating at frequencies from 460 MHz to beyond 4 GHz have been designed to be integrated in a ground-penetrating radar (GPR) positioned very close to the soil surface. FDTD modeling has allowed to define the optimal geometrical parameters associated with the ground-coupled radar system that has been studied in two polarization configurations TE and TM. The ability of the GPR system in detecting small discontinuities using polarization diversity has been analyzed considering several buried canonical objects with different dielectric characteristics. Measurements in a sand box have been compared to full-wave simulations.

In this paper, we present a software architecture that enhances the 3D visualization of sensors' data. We aim to better explore and analyze sensors' data dealing with atmospheric pollutants. Hence, our software architecture provides two techniques to interact with our geospatial data : a light web application for an easy access and visualization of this data, and a 3D GIS that allows an enhanced analysis of the geospatial data as well as the atmospheric pollutants. In consequence, this work helps at proposing better civil and urban engineering strategies in order to reduce pollution rates, and hence, enhance urban life quality.

Reliable GPS positioning in city environment is a key issue: actually, signals are prone to multipath, with poor satellite geometry in many streets. Using a 3D urban model to forecast satellite visibility in urban contexts in order to improve GPS localization is the main topic of the present article. A virtual image processing that detects and eliminates possible faulty measurements is the core of this method. This image is generated using the position estimated a priori by the navigation process itself, under road constraints. This position is then updated by measurements to line-of-sight satellites only. This closed-loop real-time processing has shown very first promising full-scale test results.

High frequency mechanical impact is a recent improvement method which is probably one of the most effective for treating welded assemblies. A number of experimental results relating to this process are presented in this article. These results lead to better understand the mechanisms of the process, to outline the influence of the operating parameters and to confirm the role played by the initial quality of treated welds. In addition, a process is proposed in order to numerically estimate the fatigue life improvement reached after treatment. All these results were obtained in the scope of a study whose long-term aim is to propose an approach that can be industrially applicable for fatigue design of welded assemblies treated by high frequency mechanical impact.

Autonomous Navigation Systems used in missiles and other high dynamic platforms are mostly dependent on the Global Positioning System (GPS). GPS users face limitations in terms of missile high dynamics and signal interference. Receiver’s tracking loops bandwidth requirements to avoid these problems are conflicting. The paper presents a novel signal frequency and phase tracking algorithm for very high dynamic conditions, which mitigates the conflicting choice of bandwidths and reduces tracking loop measurement noise. It exploits the flexibility of fuzzy control systems for directly generating the required Numerically Controlled Oscillator (NCO) tuning frequency using phase and frequency discriminators information and is labeled Fuzzy Frequency Phase Lock Loop (FFPLL). Because Fuzzy Systems can be computationally demanding and an Inertial Navigation System (INS) is often onboard the vehicle, an assisted INS Doppler version has been designed and is also proposed. Assessment of the new GPS tracking method is performed with both simulated and experimental data under jamming conditions. The main enhancements of the proposed system consist in reduced processing time, improved tracking continuity and faster reacquisition time.

The paper addresses the reconstruction of a Navier-Stokes flow in water pipes at low Reynolds numbers. A classical strategy consists of identifying optimal boundary velocities that minimize the data misfit, which is normally expressed in L2-norm. Herein, we take full advantage of the knowledge of velocity spatial shape in water pipes. As a consequence, we only determine the time evolution of the boundary velocities by the inverse approach. The minimization procedure is realized by means of the adjoint method. In a 2D water pipe junction test case, we show that the discretization error of the direct and adjoint problems can significantly deteriorate the quality of the reconstructed velocity. Then, the modeling error is analyzed in this paper. By using unsteady Stokes equations to reconstruct a Navier-Stokes flow, we may obtain an L2 error on the reconstructed velocity of about 5% for a computational cost reduced by 2 orders of magnitude.

Antennas with broadband characteristics have recently found various applications in modern ultra wide band (UWB) communication systems and in ground penetrating radar (GPR). Our applications are focused on imaging the subsurface of a large range of civil engineering structures at several depths using a bistatic GPR positioned on or close to the ground surface. The development of a compact (34*29 cm2) broadband pair of antennas operating in the frequency band from 0.27 to 3.1 GHz, whose radiation characteristics have been preliminary studied theoretically in details in different configurations, is to allow the probing of the subsurface in several frequency sub-bands using a step frequency (SF-GPR) acquisition mode. Microstrip patch antennas (MPAs) are one of the most basic and important types of planar antennas because they offer many advantages such as compact size, low-cost, ease of fabrication, light weight, and various shapes design. However, a low bandwidth and a low gain are the main shortcomings for such planar structure. The microstrip antenna has now reached maturity and many techniques have been suggested for achieving a high bandwidth such as using more complex shapes, parasitic elements, multilayer configurations and the tuning of the feed line. In this paper, an original printed rectangular slot antenna fed by a 50 Ohms CPW (coplanar waveguide) transmission line tuned by a E-shaped patch is presented. Presently, little work has been made to lower the operating frequency band of microstrip antennas at frequencies less than 0.8 MHz and to reduce the antenna size at these frequencies because major applications concern UWB wireless communications. By choosing a relative combination of a E-shaped patch, a linear feed line and a rectangular slot, we have designed an antenna structure on a FR4 substrate ( h=1.5 mm) with a very wide operating bandwidth whose nearly half of the spectrum covers frequencies lower than 1 GHz. A partial shield, only opened towards the ground, and coated with an inner layered absorbing material has been added to eliminate undesirable reflections from the upper environment particularly at low frequencies; moreover, in a GPR system, the antenna shielding will allow to reduce the coupling between the transmitting and the receiving units. The proposed rectangular slot antenna has been designed and simulated using the 3D commercial software EMPIRE based on the finite difference time domain (FDTD) technique. A detailed parameter study has allowed to define the several geometrical parameters of the unshielded slot antenna which are the result of a compromise on the frequency bandwidth (S11

International audience

In this paper, we present first a fabrication process of suspended graphene stripes. This process is done on two types of graphene sheets. One is a reduced graphene oxide and the second is a few layer graphene grown by CVD. In the second part, we introduce a new method to derive the value of the local Young’s modulus of ultrathin films using atomic force microscopy for experimental measurements and a continuum mechanics model for analytical fitting. Measurements are performed on few nanometers thick suspended graphene sheets grown by CVD.

ISBN: 978-84-695-3472-4; International audience; Using a 3D urban model to forecast satellites visibility in urban contexts in order to monitor GPS localization is the main topic of the present article. A virtual image processing is at the core of this method. A preliminary proof of concept has been presented in IEEE ITST 2011, where the theoretically visible satellites were computed with respect to the true position of the vehicle computed off-line from the data of a much more sophisticated equipment. This article addresses now the closed-loop real-time processing of the method, i.e. using the position estimated by the navigation process itself.

NDE, SEATTLE, ETATS-UNIS, 22-/05/2012 - 24/05/2012; This paper is concerned with the implementation of FO sensors in reinforcement bars (rebars) for strain measurement in reinforced concrete (RC) structures made of Ultra High Performance Fiber Reinforced Concrete. In the proposed technique, the FO sensor is embedded into a drilled cavity in the rebar using suitable adhesive. The measurement chain consists of an OBR interrogation unit (Optical Backscatter Reflectometer, based on relative Rayleigh measurements) paired with FO sensors. The validation of the proposed technique has been performed successfully through a series of experiments. In a first validation step, uniaxial tensile tests were carried out on steel rods instrumented with FO sensors. The second validation step was to demonstrate the feasibility of embedding FOsensors in RC structures (embedded into the groove of rebars or bonded on the rebars surface) without damaging them during pouring of the concrete. For this purpose, pullout samples were fabricated by partially embedding instrumented rebars in concrete blocks. Results obtained so far indicate that the sensors perform adequately for the strain measurement of rebars tested in tension and for the strain measurement of rebars embedded in a loaded RC structure.

Nanosensors dedicated to the structural health monitoring of concrete structures have been only marginally studied. They would however be particularly well-suited to monitor durability-related processes, as these phenomena involve transport of gas and liquids through micro and nano-porosity. In this paper we discuss the relevance and feasibility of embedding rela-tive humidity nanosensors within concrete. It appears that the localized, continuous knowledge of relative humidity within a concrete structure could provide a useful insight into drying shrinkage; it could also contribute to improved intrinsic permeability measurements, leading to improved assessment of structural durability. For the task, we propose a low-cost, downscalable resistive device made of a 10 nm graphene sheet grown directly on glass and atop which are ink-jet printed silver electrodes. The device resistance increases significantly with relative humidity (RH), especially above 40% RH. Relative amplitude of variations are only of about 3% for the two tested devices, but absolute variations (80 Ohms/sq and 480 Ohms/sq) appear measurable by a low-cost and robust signal conditioning electronics. Thus, the idea of using our graphene-based resistive device for embedded humidity monitoring in concrete ap-pears quite promising.

International audience; Nanoporosities play a most significant role in the durability of cementitious materials, so that nanoscale features are a promising target for SHM. However, to this day, no sensor features the resolution required to investigate non-destructively these nanofeatures. To fill in this loophole, we are devising a SHM-targeted, carbon nanotubes and graphene based capacitive ultrasonic nanotransducer for microporosity assessment in concrete. In this paper, we report on the feasibility of the key building block of the proposed sensor: we have fabricated ultra-thin graphene and single-walled carbon nanotubes membranes. A breakthrough laser vibrometry experiment shows that the membranes can feature above-nanometer amplitudes of vibration over a large range of frequencies spanning from 100 kHz to 5 MHz. A detailed numerical model of the nanotransducer shows that upon embedding in a cementitious material it could determine the volume and content of the porosity in its vicinity. Such information would be invaluable in the evaluation of structural durability.

Hipermat, KASSEL, ALLEMAGNE, 07-/03/2012 - 09/03/2012; In the frame of the French national R&D project Orthoplus, an experimental program has been carried out to assess the influence of a UHPFRC topping layer on the behaviour of orthotropic decks and their fatigue resistance. This project aims at improving the design rules for orthotropic decks and developing a UHPFRC-based innovative solution to improve the durability. Bendings tests were carried out on four specimens, consisting in a realistic steel orthotropic deck model, 2.4 x 4m, with different types and thicknesses of topping layers: traditional bituminous concrete, thin layer of UHPFRC or no topping layer. The load application has been chosen as representative of real situations and of idealised cases considered in design codes. The loads were first applied through static tests with different configurations in accordance with Eurocode 1 and then through a fatigue test representative of traffic loads during bridge lifespan.

In spite of numerous efforts for developing the applications of graphene, it remains difficult to put the remarkable physical properties of this material into devices. This is mainly due to the fact that large-area (industrial) graphene includes in its structure and on its surfaces a significant density of defects that make as many traps and scattering centres for charge carriers. The idea of the present work, contrary to diminishing the defect density, is to use the defects and the very large surface to volume ratio of that 2D material, to transform it into high sensitivity sensors. When defects are useful, low-temperature growth becomes the method that best satisfies both physical and financial demands. Here, we further decrease preparation costs by performing growth not only at low temperature directly on the final insulating substrate (glass), but also by printing the device contacts by ink-jet printing. Graphene layers actually develop at the interface between a metallic catalytic film and the insulating substrate during plasma-enhanced chemical vapour deposition (PE-CVD).1,2. Resistivity of the graphene foils was measured by the four-point methods using ink-jet printed electrods, and a resistivity as low as 820 ohms/sq were obtained. Moreover, the sensitivity of such graphene foils to water vapour was evaluated, with the prospect to use them in humidity sensors for civil engineering. In this presentation, we explain how graphite may precipitate at the interface in addition to the surface.2,3 Then we show examples of graphene obtained at temperatures in between 450 and 550°C, on glass (Fig.), fused silica, alumina and SiO2//Si. Transmission electron microscopy indicates that the structure is nanocrystalline. We finally show the humidity response of the fabricated device. Results seem to indicate that high-defect density, thin deposits are more sensitive to water vapour than thicker ones.

This paper presents two automated devices for conducting non-contact ultrasonic measurements (with air coupling and laser interferometry) for the purpose of recovering mechanical properties (porosity) on a series of concrete slabs using surface waves. The devices employed herein as part of an extensive laboratory experimental campaign are also intended to be operational onsite. The ultrasonic frequencies applied lie in the range of 40-300 kHz; moreover, according to surface wave (SW) properties, the investigation depth of a few centimetres corresponds to the cover concrete investigation target. The measurements of SW velocity and attenuation are described and used to characterise various concrete mixes. The efficiency of such measurement devices is demonstrated, within the scope of the French research project SENSO, by means of laboratory measurements carried out on manufactured cement slabs.

In this paper, we developed a numerical modeling of a sensor composed of a single mode optical fiber inserted between two thin steel ribbons that are embedded in a polyurethane-type material. The different steps of calculation are performed using the method of finite element discretization. From a mechanical view point, the ribbon transfers its applied external loading to the fiber in the unidirectional form. This transmission causes birefringence in the optical fiber by modifying the opto-geometrical parameters related to the difference between principal stresses in the fiber core. The polarization phase shift enables to evaluate the applied load. The application of this study is about the development of an instrumentation dedicated to the analysis of road traffic (vehicle WIM). The numerical results presented, show the behavior of the sensor as a function of the ribbon geometry for elastic massive under load. These results should be validated from experiments taking into account environmental characteristics and conditions of use.

A large scale equipment project, the Sense-City Equipex has received support from the French government in the framework of the 'Programme d’Investissement d’Avenir'. This project is led by the French Institute of Science and Technology for Transport, Development and Networks (IFSTTAR) with ESIEE-Paris, the Laboratory of Physics of Interfaces and Thin Films (LPICM) and the Scientific and Technical Centre for Building (CSTB) as consortium partners. Starting in 2012, Sense-City will offer a suite of high-quality facilities for the design, prototyping and performance assessment of innovative, micro- and nanotechnology based sensors devoted to urban instrumentation. Acknowledging the shortcomings of evaluating sensors performances in laboratory conditions only or in the ever-changing environment of our cities, Sense-City will provide a realistic urban test space in climatic conditions, far more complex than clean rooms and far less complex than actual cities. Sense-city revolves around the 'mini-city' concept, a large, fully customizable climatic hall able to host full- and reduced-scale models of essential urban components. The design of the models will allow for the simulation in climatic conditions of numerous scenarios of sustainable cities. The scenarios to be implemented will correspond to different research topics related to urban sustainability: energy performances in buildings, quality of air, water and soils, quality of fluid distribution networks (gas, sewage, drink water), control of waste disposal areas, durability and safety of infrastructures.

A problem arises when uniaxial tensile tests are conducted on UD composite materials in the fiber direction, that is the failure starts in the clamping area and hence the tensile strength is underestimated. In this study, uniaxial tensile tests in the fiber direction on specimens from unidirectional E-Glass fiber/Vinyl ester matrix composite material are analyzed. The effect of use of end tabs on tensile strength of specimens are investigated and finally the best configuration, including the geometry and the material of end tabs and also the clamping pressure on end tabs, is obtained through numerical simulations. mention the results.

A coplanar rectangular slot antenna operating in the very wide frequency band from 0.27 to 3.1 GHz (bandwidth over 166%) has been designed for GPR applications. The antenna, which is supposed to be positioned on the soil surface, appears particularly compact (34 £ 29 cm2) and exhibits a low cross-polarization in the E-plane. 3D FDTD simulations have allowed to make a detailed parametric study associated with the antenna dimensional parameters in order to optimize the radiating performances. The slot antenna has also been studied with a shield to be further integrated in a bistatic subsurface radar positioned on the soil surface. Simulated results of the link in the presence of a homogeneous soil then including buried objects met in civil engineering structures are presented and discussed. First experimental results on a sandy soil have been compared to numerical ones.Une antenne coplanaire rectangulaire à fente fonctionnant dans la bande de fréquence très large de 0,27 à 3,1 GHz (bande passante plus de 166%) a été conçue pour des applications GPR. L'antenne, qui est censée être positionnée sur la surface du sol, apparaît particulièrement compacte (34 par 29 cm2) et présente une faible polarisation croisée dans le plan E. Des simulations FDTD en 3D ont permis de conduire une étude paramétrique détaillée relative aux paramètres dimensionnels de l'antenne pour optimiser ses performances de rayonnement. L'antenne à fente a également été étudiée en présence d'un blindage pour être intégrée dans un radar bistatique de sub-surface positionné à la surface du sol. Les résultats simulés de la chaîne de transmission, en présence d'un sol homogène et d'objets enterrés rencontrés dans les structures de génie civil, sont présentés et discutés. Les premiers résultats expérimentaux en présence d'un sol sableux ont été comparés à des résultats numériques.

Tuned mass dampers (TMDs) are widely used in civil engineering. the performance of this device depends on their state parameters and therefore the evolution of the bridge may pull down the efficiency of this kind of device. Active tuned mass damper (ATMD) have been explored widely for applications in damping response control of bridges under construction. This paper presents a new semi-active control based on an electromechanical device. This semi-active tool consists of a pendulum coupled to an alternator. The alternator converts the mechanical energy of the oscillating pendulum into electric energy to be dissipated through an exterior resistor via Joule effect. In order to damp the torsional mode of a bridge during successive construction phases, the electromechanical actuator was connected to the bridge and its parameters were changed in real time by using a new semi-active control law. This control law, once applied to the resistor, permits to modify in real time the damping coefficients and the stiffness of the TMD with the aim of obtaining an optimal configuration for the actuator at each construction phase. Numerical and experimental validations on a small-scale bridge dynamical behaviour confirm the interest of the approach., Les amortisseurs de masse accordés (PTM) sont largement utilisés dans le génie civil. Le fonctionnement de cet appareil dépend des paramètres d'état et donc l'évolution du pont peut tirer vers le bas l'efficacité de ce type de dispositif. L'amortisseur actif de masse accordé (ATMD) a été exploré largement pour des applications dans le contrôle de la réponse d'amortissement des ponts en cours de construction. Cet article présente un nouveau contrôle semi-actif basé sur un dispositif électromécanique. Cet outil semi-actif est constitué d'un pendule couplé à un alternateur. L'alternateur transforme l'énergie mécanique du pendule oscillant en énergie électrique destinée à être dissipée par une résistance extérieure par l'intermédiaire de l'effet Joule. Afin d'amortir le mode de torsion d'un pont au cours de phases successives de la construction, l'actionneur électromécanique est relié au pont et ses paramètres ont été modifiés en temps réel en utilisant une nouvelle loi de commande semi-active. Cette loi de commande, une fois appliquée à la résistance, permet de modifier en temps réel les coefficients d'amortissement et la raideur de la DMT dans le but d'obtenir une configuration optimale de l'actionneur à chaque étape de la construction. Les validations expérimentales et numériques sur un pont à petite échelle de comportement dynamique confirment l'intérêt de la démarche.

The assessment of an Excavating Damaged Zone (EDZ) due to underground works is important in the context of radioactive waste disposal within a geological formation. Seismic surveys can pro- vide, in a non-destructive manner, information directly related to the mechanical properties of this damaged zone. However, the classical refraction method is unusable for galleries where a concrete layer caps the top surface. Moreover, other possible seismic methods like surface wave analysis can become complex to implement in such a context since guided waves are present and pass through a high-velocity concrete layer. For these reasons, the present paper will focus on an experimental feasibility study of the MASW (Multi Channel Analysis of Surface Waves) method for assessing an EDZ below a concrete layer in the specific context of the Tournemire experimental platform, which was drilled into an argillaceous formation in the Aveyron department of central France. This facil- ity is operated by IRSN (French institute for Radiological Protection and Nuclear Safety). This experimental study has been conducted in conjunction with a modelling results analysis. During an initial stage, the measurements carried out in situ are analysed and it is demonstrated that a receiv- ing profile longer than 8 m is required to distinguish the various modes. Moreover, the comparison of a hammer source and a sweep signal generated by a vibrator source shows that the latter is more appropriate when building the dispersion diagram, particularly for fundamental and first higher mode curves. A second stage shows that according to the analysis of theoretical curves for profiles with similar seismic velocities of the Tournemire platform medium, the dispersion curves are sensi- tive to EDZ characteristics. In the paper's final part, the dispersion curves obtained from the experimental seismic data are inverted using a global approach. Results of the inversion of the fundamental mode only and of both the fundamental mode and the first higher mode are com- mented upon, evidencing an improved quality for this last approach.

The aim of the study reported in this paper was to provide rational aid tools to quantify the performance of nondestructive testing (NDT) tools. This study focused on the quantification of the performance of impact–echo sources (steel balls of varied diameters), applied with a new, con-tactless robot, for duct void detection and thickness measurements in a reinforced concrete wall. Because of uncertainties during the testing, the data were analyzed in a probabilistic context, with the knowledge that on-site inspections were affected by uncertainties. The αδ method was used in this regard, where the probabilities of detection and false alarm rates were used to build receiver operating characteristic curves. The methodology was applied to data measured on the same wall with two steel ball diameters: 0.16 and 0.125 m. The quantity analyzed here was the impact–echo method (resonance) frequency. This methodology could be extended to other parameters of the impact–echo setup as well as to other NDT methods.

Recent advances in seismic inversion methods allow us to get high-resolution quantitative representations of mechanical parameters of the Earth. One of the most promising inversion method is the Full-waveform inversion (FWI) method which basically consists of an iterative data fitting process based on a local optimisation (Tarantola, 1984) and unlike conventional methods (e.g. first arrival times tomography) all the information available in the data can be handled. This method has been first applied to depth exploration (Virieux and Operto, 2009), but some authors already applied it to quantitatively image the near-surface. For example, G'elis (2005) succeeded to image cavities using synthetic data including surface waves arrivals. However one of the most important remaining challenges is the validation of the method with real field data that presents many difficulties: field data are often measured on not well-known media composed of high heterogeneity degree, important intrinsic attenuation and with prominent three dimensional effects. Considering all these difficulties, the necessity to have an experimental intermediate validation step becomes obvious. The aim is to reproduce the field experiments in a well-controlled environment at a smaller scale using a well-defined spacio-temporal scalling. The physical reduced scale modeling has several advantages compared to field-measurements: first the model physical parameters are well controlled, thus numerically repeatable; secondly, the great flexibility of the setup enables to experiment easily novel measurement configurations. This validation approach has already been first applied for geophysical imaging purposes by French (1974). Recently Bretaudeau (2010) designed an ultrasonic measurement bench called MUSC with several features that enable an excellent reproducibility of field measurements from the surface. For instance, a special attention has been paid to select a source that can be assimilated to a point source and the sensors displacements are controlled with an accuracy of 10 m. Using this experimental setup, Bretaudeau (2010) showed promising results on the inversion using the vertical component. Due to recent technological improvements (Blum et al., 2010), it is now possible to record the vertical and the horizontal components simultaneously using a new laser interferometer device which has been implemented in the MUSC measurement bench. In this context, the aim of the study presented here is to investigate numerically the benefits of the each component in the frame of the FWI method and to present the recent advances on measurements of both components on reduced physical scale models. First, the physical reduced scale model and its numerical representation will be described, then a numerical study will present the benefits provided by each component for velocities reconstructions and finally measurements of the vertical and horizontal components on the reduced physical scale model will be presented and compared to numerical simulations.

Stainless steels are playing an increasingly role in civil engineering, especially in coastal and marine constructions, where the concentration of chloride ions is higher. Their use as concrete reinforcement rebar is an interesting example of that idea. However, although some studies about the use of stainless steels in prestressing are emerging, no realistic realization has been performed. This might be due to technical lock as the high mechanical strength needed for prestressing seems to be difficult to achieve with stainless steels. Moreover, even if these mechanical characteristics could be obtain, the stress corrosion cracking behavior of this kind of grade in simu-lated concrete pore solution is unknown. In this context, the aim of this work is to study, regarding hydrogen embrittlement (HE) and chloride stress corrosion cracking (SCC), two stainless steel grades (austenitic and duplex) which were formed to pre-sent high strength. Hydrogen embrittlement resistance of the two grades was studied thanks to the ISO 15630-3 standard stress corrosion cracking test where a corrosive solution of ammonium thiocyanate NH4SCN was used. A more realistic environment was used to evaluate their susceptibility to SCC. Thus, slow strain rate tests (SSRT) were performed in a simulated degraded concrete pore solution (pH = 8) with high chlorides content ([Cl-]=17,5g.L-1). In the two cases, the results are presented and discussed with respect to the microstructure of the two stainless steel grades.

International audience; Shape Memory Alloys (SMA) o ffer new perspectives in various fi elds such as aeronautics, robotics, biomedicals, or civil engineering. E ffi cient design of such innovative systems requires both adequate material models and numerical methods for simulating the response of SMA structures. Whereas much e ffort has been devoted to developing constitutive laws for describing the behaviour of SMAs, the structural problem (i.e. the simulation of a three-dimensional SMA structure) has received far less attention, in spite of substantial di culties notably due to the strong thermomechanical coupling and the presence of physical constraints on the internal variables. The time-discretization of the evolution problem obtained is not obvious, and special care must be taken to avoid convergence di culties and ensure robustness of the numerical schemes. Computation time and ease of implementation (for instance in an existing finite element code) also are major issues that need to be addressed. In this communication are presented some recent results in that direction. A central result is a recent time-discretization scheme for the thermomechanical problem. A variational formulation is attached to the corresponding incremental problem, allowing one to prove the existence of solutions for a large class of usual SMA models. The variational nature of the problem at hand also calls for an easy implementation in an existing fi nite element code, building on well-established descend algorithms. Using that approach, the solution of the thermomechanical incremental problem is typically obtained by solving a sequence of linear thermal problems and purely mechanical (i.e. at prescribed temperature) nonlinear problems. That approach is fairly general and applies for a wide range of SMA models. The numerical scheme for solving the purely mechanical problem, however, strongly depends on the particular model that is used. In a micromechanical modelling of SMAs, the phase transformation is described locally by an internal vectorial variable which is physically constrained to satisfy a set of inequalities at each point. We show that the corresponding incremental problem can be recast as a linear complementarity problem, for which e ffcient algorithms (such as interior-point methods) are available. That reformulation essentially consists in a change of variables. In terms of variational formulation, that approach amounts to replace a convex but non-quadratic minimization problem with an equivalent quadratic minimization problem.

Eurosteel 2011, BUDAPEST, HONGRIE, 31-/08/2011 - 02/09/2011; A large-scale experimental program has been carried out at the LCPC structures laboratory to assess the influence of topping layer on the behaviour of orthotropic decks and their resistance to fatigue phenomenon. These tests have been carried out within the frame of a joint R& D project called Orthoplus, in partnership with Eiffage Company, Arcadis engineering office and the Sétra (French Highways technical authority). This project aims at improving the design rules for orthotropic deck and developing a UHPFRC-based innovative solution to improve the durability of orthotropic deck. Loads have been applied to four specimens, 4 m-long and 2.40 m-wide, consisting in a realistic steel orthotropic deck with different types of topping layers: traditional bituminous concrete, thin layer of UHPFRC, or no topping layer. The dimensions of the specimens have been chosen to limit the effect of boundary conditions on the effect of a local loading. The load application has been chosen as representative of real situations and of idealised cases considered in design codes: real truck wheels have been used as well as rectangular steel plates with dimensions complying with Eurocode 1 part 2. The investigation has been focused on the stress obtained at the weld between stiffener and deck plate, at mid-span between transverse crossbeams, which is critical to estimate the fatigue lifespan of real orthotropic deck structures under the effect of repeated local loads induced by traffic. The stress repartition in the different configurations has been assessed through static tests, then 2 million cycles have been applied to verify the fatigue resistance the specimen. The paper details the test protocol and the main results of the experimental program. Namely, the benefits of an increased rigidity provided by the UHPFRC top layer is quantified, due to the reduction in stress concentration at the critical fatigue detail.

International audience; This paper presents an approach to estimate link travel time in urban areas. This approach consists of a data fusion from underground loop detectors and probe vehicles equipped with global positioning system (GPS). This method is expected to be more accurate, reliable and robust than using either of these data sources alone. In this approach, an algorithm is developed. This algorithm is based on the unscented Kalman filter using vehicle counts and flows from loop detectors located at the end of every link, and travel time from probe vehicles. From these counts the average travel time is calculated using the "cumulative plot" method. Furthermore, in order to incorporate the GPS data, a map-matching method is used to associate a travel time to the appropriate link.

Nanoporosities play a most significant role in the durability of cementitious materials, so that nanoscale features are a promising target for structural health monitoring (SHM). However, to this day, no sensor features the resolution required to investigate non-destructively these features. To fill in this loophole, IFSTTAR is devising innovative nanoscale SHM solutions based on nanosensors. Two types of carbon nanotubes (CNT) devices are being studied: ultrasonic nanotransducers for microporosity assessment and field-effect transistors for relative humidity (RH) monitoring. A detailed numerical model of the CNT-based ultrasonic nanotransducers we are devising shows that upon embedding in a cementitious material it could determine the volume and content of the porosity in its vicinity. Such information would be invaluable in the evaluation of structural durability (Lebental et al., 2011). Our characterizations of the field-effect transistors devices we fabricated with low density CNT networks indicate that they could be exploited as a high sensitivity means to probe high RH environment such as concrete (Bondavalli et al., 2009) With such promising outputs, these two studies open up the path toward in-situ morphology and composition monitoring of the microporosity of cementitious materials by nanosensors. This nanosensors-based nanoscale knowledge is the key to detect and prevent degradations of cement-based structures. As such, it will significantly contribute to an improved sustainability in civil engineering.

A new approach is proposed to monitor in situ gamma radiation influence on Brillouin optical fiber extensometers. Experimental results are illustrated with two fiber samples under gamma radiation up to total dose of about 600Gy. The Brillouin frequency shift has poor sensitivity at such radiations level, neither the spectral Brillouin signature nor its dependence with strain. Meanwhile, propagation losses increase under radiations, with an amplitude linked to fiber dopants. The target application is Nuclear Wastes Repository Monitoring where high doses are expected. UV radiation preliminary tests show that compaction phenomenon may occur at such high doses, inducing Brillouin frequency shift up to 20 MHz.

The settlement behavior of a pile-raft foundation is analyzed with the help of a multiphase model aimed at describing the overall response of the reinforced ground. According to this model, the group of piles is treated as a homogenized continuous medium in interaction with the soil along the pile length, as well as at their lower tips. These two kinds of interaction, which play a decisive role in the way the piles are actually working as strengthening elements, are described by specific constitutive laws which can be directly introduced in the general governing equations of the multiphase model. Thus improved, the multiphase model can then be incorporated in a finite element code developed in the context of an elastoplastic behavior of the soil, provided that the constitutive parameters of the interaction laws have been previously identified. This identification procedure is performed through numerical simulations of the simple problem of a single pile, loaded at its top. The global response of vertically loaded piled-raft foundations, expressed in the form of load settlement curves, is finally presented, clearly highlighting the decisive influence of the mobilized pile shaft friction and tip resistance on the foundation settlement reduction.

Shape memory alloys (SMAs) display peculiar properties such as the superelastic behaviour or the shape memory effect, which are both the result of a solid/solid phase transformation between different crystallographic structures (known as austenite and martensite). Thanks to these properties, SMAs offer new perspectives in various fields such as aeronautics, robotics, biomedicals, or civil engineering. Efficient design of SMA systems requires both adequate material models and numerical methods for simulating the response of SMA structures. Whereas much effort has been devoted to developing constitutive laws for describing the behaviour of SMAs, the structural problem has comparatively received far less attention, and is the focus of this Communication.

International audience; For the non-destructive sounding of the sub-surface for a large range of applications, a coplanar waveguide-fed bowtie slot antenna operating in a wide frequency band [0.4;1.5] GHz has been designed. The main originality of our work is the extension of the operating frequency band of the uniplanar bowtie slot antenna to frequencies lower than 800 MHz. The shape and the dimensions of the antenna have been optimised in the presence of a soil using numerical simulations based on the finite difference time domain approach. For the characterisation of the sub-surface, a transmission link comprising a pair of bowtie slot antennas that are moved along the soil surface has been studied in details to obtain the system performance in the frequency and time domains. First experimental results have been obtained on a sandy soil in the frequency domain using a vector network analyser. The experimental data have been analysed and compared with simulations results.

Dans le contexte du sondage non destructif de la sub-surface pour une large gamme d'applications, une antenne n½ud de papillon 'bowtie' à encoche ayant pour alimentation un guide d'onde coplanaire et opérant dans une large bande de fréquence [0,4; 1.5] GHz a été conçue. La principale originalité de notre travail demeure dans l'extension de la bande de fréquences de fonctionnement de ce type d'antenne à n½ud de papillon à encoche uniplanaire à des fréquences inférieures à 800 MHz. La forme et les dimensions de l'antenne ont été optimisées en considérant un sol à partir de simulations numériques fondées sur l'approche des différences finies dans le domaine temporel. Pour la caractérisation de la sub-surface, une chaîne de transmission comprenant une paire d'antennes n½ud de papillon à encoche lesquelles ont a été déplacées linéairement à la surface du sol a été étudiée en détails afin d'obtenir les performances du système dans les domaines fréquentiel et temporel. Les premiers résultats expérimentaux ont été obtenus sur un sol sableux dans le domaine fréquentiel à l'aide d'un analyseur de réseau vectoriel. Les données expérimentales ont été analysées et comparées avec les résultats des simulations.

The state of roads is continuously degrading due to meteorological conditions, ground movements, and traffic, leading to the formation of defects, such as grabbing, holes, and cracks. In this article, a method to automatically distinguish images of road surfaces with defects from road surfaces without defects is presented. This method, based on supervised learning, is generic and may be applied to all type of defects present in those images. They typically present strong textural information with patterns that show fluctuations at small scales and some uniformity at larger scales. The textural information is described by applying a large set of linear and nonlinear filters. To select the most pertinent ones for the current application, a supervised learning based on AdaBoost is performed. The whole process is tested both on a textural recognition task based on the VisTex image database and on road images collected by a dedicated road imaging system. A comparison with a recent cracks detection algorithm from Oliveira and Correia demonstrates the proposed method's efficiency.

Time domain reflectometry (TDR) is a proven, nondestructive method for the measurement of the permittivity and electrical conductivity of soils, using electromagnetic (EM) waves. Standard interpretation of TDR data leads to the estimation of the soil’s equivalent electromagnetic properties since the wavelengths associated with the source signal are considerably greater than the microstructure of the soil. The aforementioned approximation tends to hide an important issue: the influence of the microstructure and phase configuration in the generation of a polarized electric field, which is complicated because of the presence of numerous length scales. In this paper, the influence of the microstructural distribution of each phase on the TDR signal has been studied. We propose a two-step EM modeling technique at a microscale range (200 micrometers): first, we define an equivalent grain including a thin shell of free water, and second, we solve Maxwell’s equations over the discretized, statistically distributed triphasic porous medium. Modeling of the TDR probe with the soil sample was performed using a three-dimensional finite difference time domain scheme. The effectiveness of this hybrid homogenization approach is tested on unsaturated Nemours sand with narrow granulometric fractions. The comparisons made between numerical and experimental results are promising, despite significant assumptions concerning (1) the TDR probe head and the coaxial cable and (2) the assumed effective medium theory homogenization associated with the electromagnetic processes arising locally between the liquid and solid phases at the grain scale.

The 28th PIERS Symposium, Cambridge, ETATS-UNIS, 05-/07/2010 - 08/07/2010; Road surface quality is very sensitive to mechanical properties of the undergroundstructure, and particularly to its water content. Electromagnetic frequency cross-hole radar aSsociated with a Zero Offset Profiling (ZOP) acquisition mode has been used as a non destructive technique to evaluate the vertical distribution of the water content inside a multi-layered clay sand embankment test site. In order to fit two borehole diameters (40 and 67 mm), that are used for civil engineering monitoring, two speci¯c radar transmission links (with a distance less than 1 m) have been developed to work in the frequency band [0.5; 1.5] GHz. These borehole transmission links have led to the design of two types of ultra-wideband symmetric antennas: a 3D "folded dipole" made of thin wire elements, and a planar "blade dipole". Numerical electromagnetic modeling associated with both antenna geometries, and their integration in a transmission link have been performed using two complementary FDTD softwares: a commercial software EMPIRE based on an adaptative grid, and a laboratory-made software which relies on parallel calculation and can consider a soil made of a random dielectric distribution. The comparison of measurement and simulation results with both folded and blade dipoles, has allowed to highlight contrasts of real permittivities induced by water content and soil compaction level. The attenuation profile has been evaluated by the Centroïd Frequency Downshift Method (CFDM). To reach an improved accuracy, a full-wave sensitivity analysis has been made; thus the vertical variations of the electrical conductivity that could not have been evaluated with the ray based formalism inherent to CFDM, is finally correctly estimated.

Des analyses par thermographie pulsée conduites sur des données expérimentales et simulées sont présentées. Ces méthodes sont appliquées à des données issues d'une caméra infrarouge non refroidie équipée d'un détecteur matriciel à microbolomètres (de moindre sensibilité thermique que les caméras refroidies). Les données font l'objet de calculs pour déterminer la profondeur des défauts en s'appuyant sur l'hypothèse du milieu semi-infini. Enfin, une discussion sur l'influence des performances de ce type de caméra sur la détection potentielle de défauts non émergents est proposée vis-à-vis du domaine des matériaux de structure de chaussées.

An approach is presented here to invert surface wave dispersion and attenuation relative to the depth-dependence of the visco-elastic parameters of functionally graded materials (FGMs). The particularity of this method lies in allowing visco-elastic parameters to vary continuously with depth and in properly incorporating the continuous nature of these variations into both the forward problem (the calculation of dispersion and attenuation) and the inverse problem (evaluation of visco-elastic parameters). The forward problem solves the equation of elastic motion using a Runge–Kutta integration scheme, while the inverse problem is solved with the nonlinear solution for continuous inverse problems developed by Tarantola and Valette (1982) [32] . Viscoelasticity is treated as a first-order perturbation to the elastic structure. Testing on a synthetic example shows that the procedure is able to closely reproduce the S-wave velocity and attenuation profiles. As expected, the variations in P-wave velocity are not resolved, yet they do not introduce any significant bias into the S-wave velocity profile. The Rayleigh wave phase velocity and attenuation, measured by laser ultrasonic experiments, are used to infer the depth-dependence of S-wave velocity and of attenuation on mortar samples. This depth-dependence compares well with the depth-dependence derived from the sample density inferred from gamma-densitometry.

Strengthening or retrofitting of reinforced concrete structures by externally bonded fiber-reinforced polymer (FRP) systems is now a commonly accepted and widespread technique. The use of bonding techniques, however, always requires following rigorous installation procedures. Conformance checking through an in-place auscultation of the bonded FRP systems is highly recommended. The quality control program should involve a set of appropriate inspections and tests. Because it's rapid and efficient and can be readily used in the field, active infrared thermography shows promise as a nondestructive inspection technique that can be used as a quality control check during installation.

Tuned mass dampers (TMDs) supplement existing structures with damping while preserving stability. As evolutions of the structure to be controlled may pull down the performance of this kind of device, large bridges under construction in windy areas are rather equipped with active devices such as AMDs that prove efficient (7th International Seminar on Seismic Isolation, Passive Energy Dissipation and Active Control of Vibrations of Structures, Assisi, Italy, 2001). However, active devices suffer from several drawbacks such as the necessity to carefully prevent from instability, especially in the case of noncollocated control. Therefore, a natural question arises: how to adapt a TMD in such a way to make its performance independent of the structural evolution? A new type of semi-active control system matching this requirement is presented. It builds upon a TMD of pendulum type. In order to damp the torsional mode of a bridge under construction, a gear with an alternator would connect the pendulum to the structure. As the bridge starts vibrating, the pendulum begins to oscillate and the alternator converts the mechanical energy into electrical energy to be dissipated through an exterior resistor via the Joule effect. Given an optimal design of a passive tuned pendulum damper (TPD) for the structure in its current configuration, the semi-active control strategy consists in changing the resistor in real-time in such a way to lock the apparent stiffness and damping of the real TPD at their desired optimal values no matter the current construction step. Resistor tuning is mandatory even when only one construction step is considered since a constant resistor within the alternator would yield a time-varying effective damping coefficient of the pendulum, whereas the desired optimal damping assumes a given value, which does not change until the structure or load type changes. The semi-active control law easily adapts to any change of the structure provided this change is known. The control algorithm relies on the knowledge of the pendulum rotation, of the frequency of the mode to be controlled and of its modal participation factor at the TPD location. These modal parameters are computed during the construction process, or can be viewed as outputs of a SHM system. How to get these parameters has already received a lot of attention in the SHM literature and is not discussed here. Experimental validations on a small-scale bridge mock-up confirm the interest of the approach.

Temperature variations have strong effects on structure vibrations, urging the need for accurate real-time temperature identification. The work presented here deals with the reconstruction of the thermal field inside a structure, given pointwise temperature measurements. This is achieved by reconstructing both the initial and boundary conditions. The numerical procedure uses the adjoint method, which is unable, in its usual L 2 setting, to provide accurate results at the end of the observation period. This paper shows how the introduction of regularity assumptions yields an accurate and stable real-time temperature reconstruction while keeping the generality and flexibility of the usual adjoint method.

The analysis of optical and acoustic properties of optical fibers is required for accurate Brillouin gain spectrum (BGS) determination. We present a full modal-analysis of the guided optical and acoustic modes based on a two-dimensional finite-element method (2D-FEM) for BGS calculation using COMSOL Multiphysics. We believe that this method will be helpful in analyzing and designing special fibers for applications, such as fiber amplifiers with significant SBS (Stimulated Brillouin Scattering) suppression or Brillouin-based fibersensors. The model is adapted for BGS evaluation of any single mode fiber (in term of optical mode) based on its profile, namely its geometry, and its doping composition. Compared to standard multi-layer methods limited to axially-symmetric fibers [1], the 2D-FEM analysis enables the BGS computation even for more complicated geometries, such as PANDA polarization-maintaining fiber where the optical index and the material stress are azimuthally dependant. The results of numerical modeling have shown good agreement with measured Brillouin spectra for different types of silica fibers. Examples are given for a standard GeO2-doped core fiber (standard fiber for telecommunication applications), Fluor-doped cladding fiber (acoustic anti-waveguide) and PANDA fiber.

Extraire les défauts de surface de la chaussée par traitement d'images est une tâche difficile et, dans la plupart des cas, une seule image (acquisition) est utilisée. Les difficultés liées à cette tâche sont : les changements d'illumination, les objets présents sur la route et tous les artéfacts dus à l'acquisition en dynamique. Dans cet article, nous essayons de régler une partie de ces problèmes en utilisant des acquisition de différents points de vue. En conséquence, nous présentons une nouvelle méthodologie s'appuyant sur ces étapes : détection des défauts dans chaque image, mise en correspondance entre les images puis fusion des différentes détections obtenues. Nous illustrons le gain de performances obtenus et, en particulier, comment les fausses détections peuvent être réduites.

The paper deals with the study and the implementation of an extended Kalman filter (EKF) applied to real-time 2D vehicle positioning. This has special applications in fields where inaccurate models or disturbed sensors are involved, such as in driving assistance or mobile robotics in urban area. Particular attention has been payed to the adaptation of the algorithm to the real-time conditions of data acquisition. The contribution of this work also includes some tests performed in real conditions to check the localization algorithm efficiency. To do so, a vehicle is equipped with gyroscope and odometer sensors to be fused with GPS solutions. A Mahalanobis test is also implemented to verify the GPS consistency and reject outliers. Finally, a satellite constellation prediction tool has been used, that encompasses both the planned trajectories and the GPS ephemeris, as well as the surrounding structures.

A new stable and accurate, finite-difference 2D elastic seismic wave propagation modeling algorithm is developed, with a Perfectly Matched Layer (PML) absorbing boundary condition to avoid reflections from the edges of the numerical model. This is used to study the interaction of seismic surface waves with near-surface heterogeneities. The effects of different empty cavity shapes and depths and altered zones is evaluated from the direct and diffracted seismograms and corresponding Rayleigh wave dispersion images. Differential seismograms calculated for models both with and without a cavity show a complex, non-symmetrical, diffraction pattern and their dispersion images show well-localized scattering from heterogeneities. Missing coherent energy appears in specific frequency bands, related to the cavity depth, shape and degree of modification of the surrounding medium. The cavity more strongly affects seismograms when it is shallower. A [Formula: see text] deep rectangular cavity generates more severe perturbations than a circular section, due to non-symmetrical back-scattered patterns recognized in dispersion images. Furthermore, low velocity zones around and above the cavity, due to soil alteration, trap waves and lead to increased ground roll attenuation and strong footprints in dispersion images that can possibly mask the cavity signature. If the altered zone extends to the surface as a cone, trapping phenomena completely dominate seismograms. The detection of altered zones is a very useful indication in natural hazard assessment, making it possible to distinguish the signature of a ‘safe’ cavity from a potentially dangerous one.

International audience; This paper corresponds to the second part of a study that aims at modeling helical structures accounting for translational invariance. In the Part 1 of this paper, the static behavior has been addressed using a helical homogenization approach which provides the stress state corresponding to axial loads. The latter is considered as a prestressed state, for elastic wave propagation analysis in helical waveguides, which is the subject of the Part 2 of this paper. Non destructive testing of springs and multi-wire strands is a potential application of the proposed model. Accounting for translational invariance, the elastodynamic equations of prestressed helical structures yield a 2D problem posed on the cross-section, corresponding to a so-called semi-analytical finite element (SAFE) formulation. For helical springs, the numerical model is validated with an analytical solution corresponding to a Timoshenko beam approximation. It is shown that the influence of the prestressed state is significant at low frequencies. Finally, a seven-wire strand subjected to axial loads is considered. The computed dispersion curves are compared to experimental data. Good agreement is obtained for the first compressional-like modes and their veering central frequency.