Mesure des courbes de dispersion des ondes guidées circonférentielles dans une coque elliptique par retournement temporel

Le retournement temporel permet de déterminer la position de sources acoustiques à partir du signal reçu sur un réseau de récepteurs. On s'intéresse au cas d'une source directive mobile, modélisant une onde guidée circonférentielle dans une coque, rayonnant dans le milieu extérieur. L'analyse de la forme des fronts d'onde aux récepteurs détermine la position de la source effective qui dépend de la vitesse de phase. Cette analyse a permis d'étendre au cas de sections elliptiques une méthode de mesure des courbes de dispersion déjà existante pour des sections circulaires

Characterization of a bone mimicking phantom by means of circumferential guided waves dispersion curves

International audiencePrevious studies have evidenced the circumferential propagation of waves guided by the roughly cylindrical cortical shell of the femoral neck. We hypothesize that measuring the phase velocities of such waves could yield estimates of the cortical thickness and material properties, which could improve fracture risk prediction. The objective of this study is to test the ability of the DORT method, processing based on time reversal principle, to measure circumferential guided waves in a bone-mimicking tube. The tube has the typical dimensions of the mid-femoral neck. A focused array specifically designed for this study was used for emission and reception. To serve as a noise-free reference, the experiment was also simulated based on an analytical formulation. The DORT method was applied to experimentally recorded and simulated data to retrieve the guided waves dispersion curves. Five branches of modes were obtained. They were identified by comparison with the theoretical dispersion curves of a semi-immersed plate. Experimental branches can be used in an inverse scheme to obtain estimations of the shell properties. This study shows that measuring circumferential guided waves is feasible in a structure with dimensions and material properties (elasticity, attenuation) close to those of the cortical compartment of the femoral neck

Caractérisation des effets du gonflement provoqué par la réaction alcali-silice sur le comportement mécanique d'une structure en béton

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

A review of continuum damage modelling for dam analysis Main steps of a fruitful university-industry collaboration leading to an integrated model applicable to AAR affected structures

International audienceThis article presents the different steps of a research process initiated in the field of dam engineering, through collaboration between EDF and ENS Cachan, following Jacky Mazars' pioneering work on the application of the damage concept to concrete structure modelling. Considering the importance of concrete swelling phenomena for the long-term behaviour of concrete dams, special efforts have been devoted to the development of a rheologic model in this field. This paper explains how the research performed contributed to the elaboration and the justification of the main equations included. An application to the Temple-sur-Lot dam is presented

Structures damaged by ASR and DEF: Improving the prognosis of structures damaged by expansive concrete with physico-chemical modelling

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Combination of structural monitoring and laboratory tests for assessment of Alkali-Aggregate Reaction swelling: application to gate structure dam

International audienceSince 1964, the Temple sur Lot dam, built in south west of France in 1948, has presented continuous AAR induced displacements despite low and relatively constant alkali content in the concrete and non-significant residual swelling test results. The authors have shown, based on MEB observations and SEM analysis, that substitution process between alkali and calcium into the AAR gel could explain this long term dam’s behaviour. As calcium substitution phenomenon is very slow, it cannot be detected using a classical residual swelling test, so an original method to assess the AAR kinetic and the residual swelling capability is proposed. This method consists first in a laboratory test dealing with the silica consumption kinetic and secondly in a numerical finite element inverse analysis of the dam which include the consumption kinetic measured in laboratory. The final swelling amplitude is thus fitted from one observed structural displacement rate. The model prediction capability is validated through the comparison between the evolutions of displacement of instrumented points predicted by the calculations (unused for the fitting) and the evolutions measured on the dam. At last, calculations have been performed in order to predict the displacements and the damage fields of the dam for the next decades

Combination of structural monitoring and laboratory tests for assessment of Alkali-Aggregate Reaction swelling: application to gate structure dam

International audienceSince 1964, the Temple sur Lot dam, built in south west of France in 1948, has presented continuous AAR induced displacements despite low and relatively constant alkali content in the concrete and non-significant residual swelling test results. The authors have shown, based on MEB observations and SEM analysis, that substitution process between alkali and calcium into the AAR gel could explain this long term dam’s behaviour. As calcium substitution phenomenon is very slow, it cannot be detected using a classical residual swelling test, so an original method to assess the AAR kinetic and the residual swelling capability is proposed. This method consists first in a laboratory test dealing with the silica consumption kinetic and secondly in a numerical finite element inverse analysis of the dam which include the consumption kinetic measured in laboratory. The final swelling amplitude is thus fitted from one observed structural displacement rate. The model prediction capability is validated through the comparison between the evolutions of displacement of instrumented points predicted by the calculations (unused for the fitting) and the evolutions measured on the dam. At last, calculations have been performed in order to predict the displacements and the damage fields of the dam for the next decades

DEF modelling based on thermodynamic equilibria and ionic transfers for structural analysis

International audienceDelayed ettringite formation (DEF) is a process which can lead to swelling and cracking of concrete. This paper proposes a chemical model to predict the kinetics and the amount of DEF in concretes subjected to high-temperature curing. The modelling considers several types of phenomena: the thermodynamic equilibria of hydrate crystallisation, the binding of ionic species to hydrated calcium silicates and the mass balance equations, which include the diffusion mechanisms. All the constitutive equations are provided and the thermodynamic constants found from a wide-ranging literature review are given in particular detail. The model has been implemented in a finite element code. The numerical results give the amount of ettringite and monosulphates, and ionic concentration fields in the simulated structure. They are compared with experimentation in which the early-age thermal cycle and long-term alkali release combine to cause DEF

ASSESSMENT OF A CONCRETE DAM AFFECTED BY AN INTERNAL SWELLING REACTION (ISR)

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