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Sceaux, France

Limongelli M.P.,Polytechnic of Milan | Siegert D.,University Paris Est Creteil | Merliot E.,University Paris Est Creteil | Vidal R.,Advitam | And 5 more authors.
MATEC Web of Conferences | Year: 2015

In this paper are reported the results of an experimental campaign carried out on a post tensioned concrete beam with the aim of investigating the possibility to detect early warning signs of deterioration basing on static and/or dynamic tests. The beam was tested in several configurations aimed to reproduce several different phases of the 'life' of the beam: the original undamaged state, increasing loss of tension in the post tensioning cables, a strengthening intervention carried out by means of a second tension cable, formation of further cracks on the strengthened beam. Responses of the beam were measured by an extensive set of instruments consisting of accelerometers, inclinometers, displacement transducers, strain gauges and optical fibres. The paper discusses the tests program and the dynamic characterization of the beam in the different damage scenarios. The modal properties of the beam in the different phases were recovered basing on the responses recorded on the beam during sine-sweep and impact hammer tests. The variation of the first modal frequency was studied to investigate the sensitivity of this parameter to both the cracking of the concrete section and the tension in the cables and also to compare results given by different types of experimental tests. © 2015 Owned by the authors, published by EDP Sciences. Source

Buffo-Lacarriere L.,CNRS Materials and Construction Durability Laboratory | Barre F.,Geodynamique et Structure | Chauvel D.,Electricite de France | Darquennes A.,Ecole Normale Superieure de Cachan | And 9 more authors.
European Journal of Environmental and Civil Engineering | Year: 2015

Within the CEOS.fr national research project, several experiments on massive concrete structures were conducted to improve the knowledge on the cracking phenomenon. In this paper, experiments where deformations at early age are restrained are presented. Testing bodies are I-shaped and two largely dimensioned steel struts are placed laterally between the two transverse heads to prevent almost any shrinkage. Three testing bodies were realized: RG8, the reference one; RG9, with a reduced reinforcement and RG10, with an increased cover. A full set of measurement was used for auscultation of these beams during early age. Optical long base fibres gave information on the relative displacement of the central part of the beam. Local measurements of strains in concrete were given thanks to Vibrating Wire Extensometers. Gauges on rebars produced data of the strain on the first reinforcement layer, and the force in struts was monitored. With this, the force and stresses in concrete and rebars could be deduced. This huge amount of data allows verifying the phenomenology of the concrete. Various hypotheses were analysed to explain the strain measured and the corresponding forces in each component during specific period of early age. A first analysis of the cracking process shows that the cracks could appear for stresses below the tensile strength. © 2015 Taylor & Francis Source

Tardieu N.,Electricite de France | Cheignon E.,NECS
European Journal of Computational Mechanics | Year: 2012

In this article a Newton-Krylov method is discussed, which is part of the inexact Newton's methods family. They combine iterative solution methods, especially Krylov methods (conjugate gradient, GMRES, etc.) with the Newton's method, whereas, in solid mechanics, direct solvers are often preferred for the solution of linearised systems. After having introduced a versatile and robust preconditioner, we discuss the efficiency of this approach on a highly non-linear industrial problem. © 2012 Taylor & Francis. Source

Ghavamian S.,NECS | Jason L.,CEA Saclay Nuclear Research Center | Bonenfant J.,NECS
European Journal of Environmental and Civil Engineering | Year: 2010

The seismic behavior of reinforced concrete structures is generally evaluated through modal spectral approaches, based on linear elastic analysis. In the case of seismic reevaluation of existing structures using traditional methods, since the nonlinear behavior of materials is not taken into account, these techniques often lead to an overestimation of the needs in reinforcement. In this contribution, it is proposed to highlight how including nonlinearity in the mechanical behavior of concrete and steel can improve the seismic evaluation of RC structures. For this purpose, a pushover technique is applied on an office building. Contrary to a classical approach, the progression of the failure mode and the mechanical degradation can be obtained and used to accurately elaborate the best retrofitting strategy. Some improvements of the constitutive laws are nevertheless needed if the use of this type of approaches is to be extended to more complex structures. However, the maturity of most constitutive models is not enough to allow industrial applications. © 2010 Lavoisier, Paris. Source

Seyedi D.M.,Bureau de Recherches Geologiques et Minieres | Gehl P.,Bureau de Recherches Geologiques et Minieres | Douglas J.,Bureau de Recherches Geologiques et Minieres | Davenne L.,NECS | And 2 more authors.
Earthquake Engineering and Structural Dynamics | Year: 2010

Fragility curves are generally developed using a single parameter to relate the level of shaking to the expected structural damage. The main goal of this work is to use several parameters to characterize the earthquake ground motion. The fragility curves will, therefore, become surfaces when the ground motion is represented by two parameters. To this end, the roles of various strong-motion parameters on the induced damage in the structure are compared through nonlinear time-history numerical calculations. A robust structural model that can be used to perform numerous nonlinear dynamic calculations, with an acceptable cost, is adopted. The developed model is based on the use of structural elements with concentrated nonlinear damage mechanics and plasticity-type behavior. The relations between numerous ground-motion parameters, characterizing different aspects of the shaking, and the computed damage are analyzed and discussed. Natural and synthetic accelerograms were chosen/computed based on a consideration of the magnitude-distance ranges of design earthquakes. A complete methodology for building fragility surfaces based on the damage calculation through nonlinear numerical analysis of multi-degree-of-freedom systems is proposed. The fragility surfaces are built to represent the probability that a given damage level is reached (or exceeded) for any given level of ground motion characterized by the two chosen parameters. The results show that an increase from one to two ground-motion parameters leads to a significant reduction in the scatter in the fragility analysis and allows the uncertainties related to the effect of the second ground-motion parameter to be accounted for within risk assessments. Copyright © 2009 John Wiley & Sons, Ltd. Source

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