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Modelling chloride penetration in concrete using electrical voltage and current approaches
Lizarazo-Marriaga, Juan;Claisse, Peter;
Materials Research , 2011, DOI: 10.1590/S1516-14392011005000008
Abstract: this paper reports a research programme aimed at giving a better understanding of the phenomena involved in the chloride penetration in cement-based materials. the general approach used was to solve the nernst-planck equation numerically for two physical ideal states that define the possible conditions under which chlorides will move through concrete. these conditions are named in this paper as voltage control and current control. for each condition, experiments and simulations were carried out in order to establish the importance of electrical variables such as voltage and current in modelling chloride transport in concrete. the results of experiments and simulations showed that if those electrical variables are included as key parameters in the modelling of chloride penetration through concrete, a better understanding of this complex phenomenon can be obtained.
Prediction of residual stress due to early age behaviour of massive concrete structures: on site experiments and macroscopic modelling  [PDF]
Jihad Zreiki,Vincent Lamour,Mohend Chaouche,Micheline Moranville
Physics , 2008,
Abstract: Early age behaviour of concrete is based on complex multi-physical and multiscale phenomena. The predication of both cracking risk and residual stresses in hardened concrete structures is still a challenging task. We propose in this paper a practical method to characterize in the construction site the material parameters and to identify a macroscopic model from simple tests. We propose for instance to use a restrained shrinkage ring test to identify a basic early age creep model based on a simple ageing visco-elastic Kelvin model. The strain data obtained from this test can be treated through an early age finite element incremental procedure such that the fitting parameters of the creep law can be quickly identified. The others properties of concrete have been measured at different ages (elastic properties, hydration kinetics, and coefficient of thermal expansion). From the identified early age model, we computed the temperature rise and the stress development in a non reinforced concrete stress for nuclear waste. The good agreement between in-situ measurement and predicted behaviour allowed us to validate our approach.
Residual Strengths of Reinforced Concrete Beams With Heavy Deterioration
Wei-lun Wang,Ju Chen
Research Journal of Applied Sciences, Engineering and Technology , 2011,
Abstract: This study focused on the residual strengths of reinforced concrete beams with heavy deterioration. This work is based on experimental investigation of reinforced concrete beams naturally corroded over 30 years. Visual inspection was firstly conducted and the concrete cracking, spalling of concrete cover, corrosion of rebar were recorded. Material tests on concrete and corroded rebar were also conducted. Loading tests were performed on three corroded beams. The residual bending strengths obtained from the test results were compared with design strengths of uncorroded beam. It is shown that the corroded beams lost most of their strengths. Finite element model was developed to further investigate the behaviour of corroded reinforced concrete beams. The element type and mesh, boundary condition and load application, and material model were considered in the nonlinear finite element model. The effect of concrete cover spalling, rebar corrosion and midspan vertical crack on the residual strength of corroded reinforced concrete beams were analyzed using the developed model.
Computational modelling of failure mechanisms in reinforced concrete structures  [PDF]
Mark Peter,Bender Michél
Facta Universitatis Series : Architecture and Civil Engineering , 2010, DOI: 10.2298/fuace1001001m
Abstract: A modelling approach for macroscopic reinforced concrete (RC) structures and structural elements under static loading conditions is presented. It uses the embedded modelling technique to separately account for concrete volumes and single longitudinal bars or stirrups. The material equations of the 3D elasto-plastic damage model for concrete are derived assuming isotropic damage, stiffness recovery and loss due to crack closing and reopening and a non-associated flow rule. Suitable material functions and material parameters as well as a regularisation by energy criteria are given. The approach is applied to shear beam tests illustrating numerical results compared to corresponding experimental data.
Mathematical Modelling in Placing of Fresh Concrete  [PDF]
Ahmet Bilgil
Engineering (ENG) , 2011, DOI: 10.4236/eng.2011.33023
Abstract: The main problem in working with fresh concrete is the aggregate segregation during filling of formwork. The segregation is strongly related to W/C (Water/Cement) ratio. The fresh concrete is usually considered as a Non-Newtonian fluid since it is a mixture of aggregate, cement and water. The flow behavior of the fresh concrete to W/C ratio plays a crucial role in the quality of the high performance concretes by affecting the flow behavior of the fresh concrete. The aggregates in the fresh concrete usually cause segregation in the final product depending on the flow condition. In this study, the mechanism of segregation in such systems was theoretically investigated. The mould filling of fresh concrete was numerically investigated and aggregates were considered as Lagrangian particles and segregation was identified from trajectories of such particles. It was found that the aggregates were trapped at the dead zones leading to segregation in the system. The particle size and geometry of the mould was found to have significantly affect the segregation in the system.
Bayesian Approaches to Copula Modelling  [PDF]
Michael Stanley Smith
Statistics , 2011, DOI: 10.1093/acprof:oso/9780199695607.001.0001
Abstract: Copula models have become one of the most widely used tools in the applied modelling of multivariate data. Similarly, Bayesian methods are increasingly used to obtain efficient likelihood-based inference. However, to date, there has been only limited use of Bayesian approaches in the formulation and estimation of copula models. This article aims to address this shortcoming in two ways. First, to introduce copula models and aspects of copula theory that are especially relevant for a Bayesian analysis. Second, to outline Bayesian approaches to formulating and estimating copula models, and their advantages over alternative methods. Copulas covered include Archimedean, copulas constructed by inversion, and vine copulas; along with their interpretation as transformations. A number of parameterisations of a correlation matrix of a Gaussian copula are considered, along with hierarchical priors that allow for Bayesian selection and model averaging for each parameterisation. Markov chain Monte Carlo sampling schemes for fitting Gaussian and D-vine copulas, with and without selection, are given in detail. The relationship between the prior for the parameters of a D-vine, and the prior for a correlation matrix of a Gaussian copula, is discussed. Last, it is shown how to compute Bayesian inference when the data are discrete-valued using data augmentation. This approach generalises popular Bayesian methods for the estimation of models for multivariate binary and other ordinal data to more general copula models. Bayesian data augmentation has substantial advantages over other methods of estimation for this class of models.
Residual Compressive Strength of Laterized Concrete Subjected to Elevated Temperatures  [cached]
Robert M. Brooks
Research Journal of Applied Sciences, Engineering and Technology , 2010,
Abstract: This research presents the results of an experimental program to investigate the strength performance of laterized concrete (LATCON) when subjected to elevated temperatures of 200, 400 and 600oC. Six concrete mixes incorporating 0, 10, 20, 30, 40 and 50% Laterite as a replacement by weight of sand was prepared. After heat pretreatment specimens were cooled using either rapid cooling (water-cooling) or natural cooling (air-cooling). An analysis of variance test shows that exposure temperature, cooling regime, and their interaction have a significant influence on the compressive strength of the samples. When subjected to the investigated temperatures specimens experienced strength losses that increased with temperature. This study further reveals that air-cooled concrete specimens maintained higher residual strength values than water-cooled specimens. A comparison of the residual compressive strength data obtained in this study with code provisions in Eurocode and CEB design curve shows that these codes could be applied to LATCON subjected to temperature below 400oC.
Concepts and approaches for marine ecosystem research with reference to the tropics
Wolff,Matthias;
Revista de Biología Tropical , 2002,
Abstract: the present article gives an overview on the leading concepts and modelling approaches for marine ecosystems? research including (1) the trophodynamic theory of pelagic ecosystems, (2) compartment/network models, (3) mesocosm experiments and (4) individual based modelling approaches and virtual ecosystems (ve). the main research questions addressed, as well as the potential and limits of each approach, are summarized and discussed and it is shown how the concept of ecosystem has changed over time. aquatic biomas spectra (derived from the theory of pelagic ecosystems) can give insight into the trophic structure of different systems, and can show how organism sizes are distributed within the system and how different size groups participate in the system?s metabolism and production. compartment/network models allow for a more detailed description of the trophic structure of ecosystems and of the energy/biomass fluxes through the explicit modelling of p/b-and food consumption rates and biomasses for each system compartment. moreover, system indices for a characterization and comparison with other systems can be obtained such as average trophic efficiency, energy throughput, and degree of connectivity, degree of maturity, and others. recent dynamic extensions of trophic network models allow for exploring past and future impacts of fishing and environmental disturbances as well as to explore policies such as marine protected areas. mesocosm experiments address a multitude of questions related to aquatic processes (i.e. primary production, grazing, predation, energy transfer between trophic levels etc.) and the behaviour of organisms (i.e. growth, migration, response to contaminants etc.) under semi-natural conditions. as processes within mesocosms often differ in rate and magnitude from those occurring in nature, mesocosms should be viewed as large in vitro experiments designed to test selected components of the ecosystem and not as an attempt to enclose a multitude of in
Examples of feedback, experimental and theoretical approaches for concrete durability assessment  [cached]
Lion M.,Le Pape Y.,Toutlemonde F.,Jeanpierre A.
EPJ Web of Conferences , 2011, DOI: 10.1051/epjconf/20111203003
Abstract: This paper presents some experimental data obtained from UHPFRC (Ultra-High Performance Fibre-Reinforced Concrete) being exposed for 10 years in a cooling tower and a high slag content concrete being exposed for 30 years in a marine environment. Experimental data are then used for assessing concrete durability through a theoretical approach, namely performance-based analysis. The results from the application of this approach are consistent with the penetration depth of aggressive agents measured from core samples. Finally a simulation method currently being developed by EDF is presented, which has great relevance to durability assessment.
Concepts and approaches for marine ecosystem research with reference to the tropics
Matthias Wolff
Revista de Biología Tropical , 2002,
Abstract: The present article gives an overview on the leading concepts and modelling approaches for marine ecosystems’ research including (1) The trophodynamic theory of pelagic ecosystems, (2) Compartment/network models, (3) Mesocosm experiments and (4) Individual based modelling approaches and virtual ecosystems (VE). The main research questions addressed, as well as the potential and limits of each approach, are summarized and discussed and it is shown how the concept of ecosystem has changed over time. Aquatic biomas spectra (derived from the theory of pelagic ecosystems) can give insight into the trophic structure of different systems, and can show how organism sizes are distributed within the system and how different size groups participate in the system’s metabolism and production. Compartment/network models allow for a more detailed description of the trophic structure of ecosystems and of the energy/biomass fluxes through the explicit modelling of P/B-and food consumption rates and biomasses for each system compartment. Moreover, system indices for a characterization and comparison with other systems can be obtained such as average trophic efficiency, energy throughput, and degree of connectivity, degree of maturity, and others. Recent dynamic extensions of trophic network models allow for exploring past and future impacts of fishing and environmental disturbances as well as to explore policies such as marine protected areas. Mesocosm experiments address a multitude of questions related to aquatic processes (i.e. primary production, grazing, predation, energy transfer between trophic levels etc.) and the behaviour of organisms (i.e. growth, migration, response to contaminants etc.) under semi-natural conditions. As processes within mesocosms often differ in rate and magnitude from those occurring in nature, mesocosms should be viewed as large in vitro experiments designed to test selected components of the ecosystem and not as an attempt to enclose a multitude of interacting processes. Models that use individual organisms as units can provide insight into the causes of natural variability within populations (growth, phenotype, behaviour) and into the role of intraspecific variation for interspecific processes, succession, and feedback mechanisms. In biological oceanography, interdisciplinary research is increasingly using "Virtual Ecosystems" to simulate non-linear interactions between the dynamics of fluctuating ocean circulation, the physics of air-sea interaction, turbulence and optics, biogeochemistry, and the physiology and behaviour of plankton, wh
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