The GRAVITY+ Project: Towards All-sky, Faint-Science, High-Contrast Near-Infrared Interferometry at the VLTI

The GRAVITY instrument has been revolutionary for near-infrared interferometry by pushing sensitivity and precision to previously unknown limits. With the upgrade of GRAVITY and the Very Large Telescope Interferometer (VLTI) in GRAVITY+, these limits will be pushed even further, with vastly improved sky coverage, as well as faint-science and high-contrast capabilities. This upgrade includes the implementation of wide-field off-axis fringe-tracking, new adaptive optics systems on all Unit Telescopes, and laser guide stars in an upgraded facility. GRAVITY+ will open up the sky to the measurement of black hole masses across cosmic time in hundreds of active galactic nuclei, use the faint stars in the Galactic centre to probe General Relativity, and enable the characterisation of dozens of young exoplanets to study their formation, bearing the promise of another scientific revolution to come at the VLTI.Comment: Published in the ESO Messenge

Le rôle du retour d’expérience dans l’ingénierie des barrages

L’examen de la typologie des barrages met en évidence la diversité des conceptions, des techniques d’exécution et des conditions de site. Les enseignements tirés des réussites mais aussi des échecs rencontrés ont fortement influencé les évolutions de la législation et des principes de conception. Les informations accumulées à partir des mesures d’auscultation alimentent la compréhension du comportement des ouvrages, en parallèle avec les développements scientifiques menés, en particulier sur la rhéologie des matériaux

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

International audienc

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

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

Extensive data basis for validating ASR models : A french contribution to the re-assessment of ASR-affected structures

12th International Conference on Alkali-Aggregate Reaction in Concrete, Beijing, CHINE, 15-/10/2004 - 19/10/2004Re-assessment of ASR-affected structures is a major concern for bridge an dam owners in France, for whom validated models are needed, capable of predicting the behavior and residual bearing capacity of concerned works. Such computations shall especially correctly estimate moisture influence on observed expansions, and steel reinforcement effects. With this aim, a large experimental program was carried out at the Laboratoire Central des Ponts et Chaussées (LCPC : Public Works Research Agency), with Electricité de France (EDF: French Power Company) as a partner. Results mainly consist in the mechanical evolution of 4 reactive plain or reinforced concrete beams, and 2 non-reactive companion specimens. These 3-m long structures have been submitted to intense differential moisture conditions, leading to differential ASR-progress and subsequent significant deformations. After 14 months drying phase, effect of late water supply was checked. Thermal and moisture environment, water movements within the structure, strains along the three principal axes and deflections along the beams, were precisely and redundantly measured, and complemented by crack survey and bending tests, up to failure, after 2 years-aging of the beams. Analysis of these data and validation of models is made possible by and associated extensive characterization of concrete mix-designs, including mechanical characteristics, concrete expansive properties determined on companion standard cylinders or prisms, or from residual expansion tests, drying shrinkage, and strain evolutions of cylinders, both longitudial and transversally, submitted to 3 X 3 conditions of axial load and lateral restraint, which helps estimating the complete range of chemo-chemical and reverse couplings. This material and structural experimental basis is worth using it as a benchmark for numerical modeling and engineers computation methods. Moreover, fundamental questions concerning ASR-mechanisms and structural effects can be addressed, or revisited, thanks to these results

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

Impact of stresses and restraints on ASR expansion

International audienceSome large civil engineering structures, principally certain concrete dams, are subject to the structural effects of Alkali-silica reaction (ASR). Due to the directions of loading and reinforcement, the stress state is mostly anisotropic. The aim of this paper is to describe the impact of applied stresses and restraint due to reinforcement or boundary conditions on ASR-expansion and induced anisotropic cracking. After the definition and validation of the poromechanical modelling, the paper gives a detailed description of the effects of different aspects of stress (in one, two or three directions) and reinforcement on ASR-expansion for engineers in charge of damaged structures. (C) 2017 Elsevier Ltd. All rights reserved

IMPACT OF MULTI-AXIAL STRESSES ON ASR EXPANSION

International audienc