1,721,035 research outputs found
Simulation of cavitation in water saturated porous media considering effects of dissolved air
Full text linkAn extension of a mathematical model for non-isothermal multiphase materials to consider the dissolution of air in liquid water and air mass sources during its desorption at lower water pressure is presented. The solid skeleton is assumed elasto-plastic; heat, water and air flows and water phase changes are taken into account. Physics of air dissolution and desaturation due to the air released from liquid water during cavitation in porous media are discussed. A numerical example where cavitation develops during shear band development in undrained water-saturated dense sands is solved with the developed model as discretized in space and time with the Finite Element Method
Assessment of the spalling risk for concrete at high temperature by means of computer simulation
No full textMathematical model of hydro-thermal phenomena in porous media, considering air dissolved in water
No full textInvited lecture
Reliability of simplified mathematical models of concrete degradation at fire conditions - a comparative study
No full textModeling hygro-thermal performance and strains of cementitious building materials maturing in variable conditions
No full textA novel model of hygro-thermal performance of cement-based building materials during their maturing, considering evolution of their strength properties and deformations (shrinkage and creep strains), described in terms of effective stress is briefly presented. Creep is described by means of the modified microprestress - solidification theory by Bazant et al., with some modifications to take into account the effects of temperature and relative humidity on the cement hydration. Shrinkage strains are modeled by using effective stresses in the form introduced by Gray and Schrefler, giving a good agreement with experimental data also for low values of relative humidity. Results of three numerical examples based on the real experimental tests are solved to validate the model. They demonstrate its possibilities to analyze both autogenous deformations in maturing cementitious materials, and creep and shrinkage phenomena, in building elements of different age, sealed or drying at various conditions
Towards prediction of the thermal spalling risk through a multi-phase porous media model of concrete
No full textPhysical phenomena in heated concrete, leading to thermal spalling are discussed. Contribution of the stored elastic energy and vapour pressure build-up to the kinetic energy of spalled concrete pieces is estimated. A mathematical model of hygro-thermochemo-mechanical phenomena in heated concrete is presented. Different simplified models of thermal spalling are used to define special indexes, aiming for quantitative assessment of its risk. These are tested for the results of numerical simulations based on an experimental test. A simplified energy analysis to estimate the kinetic energy of spalled concrete pieces and to make predictions about explosive or nonviolent character of the phenomenon is proposed
Modelling creep and shrinkage of concrete by means of effective stresses
No full textA novel model of mechanical performance of concrete at early ages and beyond, and in particular, evolution of its strength properties (aging) and deformations (shrinkage and creep strains), described in terms of effective stress is briefly presented. This model reproduces such phenomena known from experiments like drying creep or some additional strains, as compared to pure shrinkage, which appear during autogenous deformations of a maturing, sealed concrete sample. Creep is described by means of the modified microprestress-solidification theory with some modifications to take into account the effects of temperature and relative humidity on concrete aging. Shrinkage strains are modelled by using effective stresses giving a good agreement with experimental data also for low values of relative humidity. Results of four numerical examples based on the real experimental tests are solved to validate the model. They demonstrate its possibilities to analyze both autogenous deformations in maturing concrete, and creep and shrinkage phenomena, including drying creep, in concrete elements of different age, sealed or drying, exposed to external load or without any load
Hygro-thermo-chemo-mechanical modelling of concrete at early ages and beyond. Part II: Shrinkage and creep of concrete
No full textIn Part I of this paper (Int. J. Numer Meth. Eng., in print) a mechanistic model of hygro-thermochemical performance of concrete at early ages has been introduced. Additionally, as compared to the existing models (e.g. J. Eng. Mech. (ASCE) 1995; 121(7):785-794; 1999; 125(9):1018-1027), an effect of relative humidity on cement hydration rate and associated hygro-thermal phenomena have been taken into account. Here we deal with mechanical performance of concrete at early ages and beyond, and in particular, evolution of its strength properties (aging) and deformations (shrinkage and creep strains), described by using the effective stress concept. This allow us for explanation and modelling of phenomena known from experiments, like drying creep (e.g. Mathematical Modeling of Creep and Shrinkage of Concrete. Wiley: Chichester, 1988), or some additional strains, as compared to pure shrinkage, which appear during autogenous deformations of a maturing, sealed concrete sample (e.g. Cement Concrete Res. 2003; 33:223-232). Creep is described by means of the modified microprestress-solidification theory by Bazant et al. (J. Eng. Mech. (ASCE) 1997; 123(11):1188-1194; 1195-1201), with some modifications to take into account the effects of temperature (Comput. Struct. 2002; 80:1511-1521) and relative humidity (Int. J Numer. Meth. Eng., in print; Proceedings of the 5th World Congress for Computational Mechanics (WCCM), Vienna, Austria, 7-12 July 2002), on concrete aging. Shrinkage strains are modelled by using the effective stress principle in the form introduced by Gray and Schrefler (Eur J. Mech. AlSolids 2001; 20:521-538; Appl. Mech. Rev. (ASME) 2002; 55(4):351-388), giving a good agreement with experimental data also for lower values of relative humidity.
Two numerical examples showing comparison of the results obtained by means of our model with some published experimental data are presented. The third one, concerning 2D axial symmetric case, proves numerical robustness of the developed software. All these examples demonstrate the possibilities of the model to analyse both autogenous deformations in maturing concrete and creep phenomena, including drying creep, in concrete elements of different age, sealed or drying, exposed to external load or without any load
Modelling of autogenous hygro-thermal phenomena in massive concrete structures - a case study
No full text- …
