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• Thermo-Chemo-Mechanical Model for Concrete. II: Damage and Creep

  M. Cervera, J. Oliver, T. Prato

  Journal of Engineering Mechanics (1999). Vol. 125 (9), pp. 1028-1038

  
  

  Abstract

  In this work a coupled thermo-chemo-mechanical model for the behavior of concrete at early ages is proposed. This paper presents the formulation and assessment of the mechanical aspects of the model. Short- and long-term mechanical behaviors are modeled via a viscoelastic damage model that accounts for the aging effects. The short-term model is based on the framework of the continuum damage mechanics theory. A novel normalized format of the damage model is proposed, so that the phenomenon of aging is accounted for in a natural fashion. Long-term effects are included by incorporating a creep model inspired in the microprestress-solidification theory.

  Abstract
  In this work a coupled thermo-chemo-mechanical model for the behavior of concrete at early ages is proposed. This paper presents the formulation and assessment of the mechanical [...]

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• Thermo-chemo-mechanical model for concrete. I: Hydration and aging

  M. Cervera, T. Prato, J. Oliver

  Journal of Engineering Mechanics (1999). Vol. 125 (9), pp. 1018-1027

  
  

  Abstract

  In this work a coupled thermo-chemo-mechanical model for the behavior of concrete at early ages is proposed. The model allows simulation of the observed phenomena of hydration, aging, damage, and creep. It is formulated within an appropriate thermodynamic framework, from which the state equations are derived. In this first part, the formulation and assessment of the thermochemical aspects of the model are presented. It is based on the reactive porous media theory, and it can accurately predict the evolution in time of the hydration degree and the hydration heat production. The evolution of the compressive and tensile strengths and elastic moduli is related to the aging degree, a concept introduced to account for the effect of the curing temperature in the evolution of the mechanical properties. The short- and long-term mechanical behavior is modeled by means of a viscoelastic damage model that accounts for the aging effects. The formulation and assessment of the mechanical part of the model are relegated to a companion paper.

  Abstract
  In this work a coupled thermo-chemo-mechanical model for the behavior of concrete at early ages is proposed. The model allows simulation of the observed phenomena of hydration, [...]

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• Estudios de ingeniería sismológica y sísmica

  J. Canas

  Monograph Series in Earthquake Engineering, editor A. H. Barbat (1995). MIS13, ISBN: 84-87867-57-X

  
  

  Abstract

  El trabajo que se presenta consiste en el estudio del factor anelástico Q en la Península Ibérica obtenido a partir de la información extraida de distintas ondas sísmicas registrada en estaciones sismográficas localizadas en la propia Península y en la zona Pirenaica Francesa.

  Abstract
  El trabajo que se presenta consiste en el estudio del factor anelástico Q en la Península Ibérica obtenido a partir de la información extraida [...]

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• Strong discontinuities and continuum plasticity models: the strong discontinuity approach

  M. Cervera, O. Manzoli, J. Oliver

  International Journal of Plasticity (1999). Vol. 15 (3), pp. 319-351

  
  

  Abstract

  The paper presents the Strong Discontinuity Approach for the analysis and simulation of strong discontinuities in solids using continuum plasticity models. Kinematics of weak and strong discontinuities are discussed, and a regularized kinematic state of discontinuity is proposed as a mean to model the formation of a strong discontinuity as the collapsed state of a weak discontinuity (with a characteristic bandwidth) induced by a bifurcation of the stress–strain field, which propagates in the solid domain. The analysis of the conditions to induce the bifurcation provides a critical value for the bandwidth at the onset of the weak discontinuity and the direction of propagation. Then a variable bandwidth model is proposed to characterize the transition between the weak and strong discontinuity regimes. Several aspects related to the continuum and, their associated, discrete constitutive equations, the expended power in the formation of the discontinuity and relevant computational details related to the finite element simulations are also discussed. Finally, some representative numerical simulations are shown to illustrate the proposed approach.

  Abstract
  The paper presents the Strong Discontinuity Approach for the analysis and simulation of strong discontinuities in solids using continuum plasticity models. Kinematics [...]

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• On the formulation of coupled thermoplastic problems with phase-change

  C. Agelet de Saracibar, M. Cervera, M. Chiumenti

  International Journal of Plasticity (1999). Vol. 15 (1), pp. 1-34

  
  

  Abstract

  This paper deals with a numerical formulation for coupled thermoplastic problems including phase-change phenomena. The final goal is to get an accurate, efficient and robust numerical model, allowing the numerical simulation of solidification processes in the metal casting industry. Some of the current issues addressed in the paper are the following. A fractional step method arising from an operator split of the governing differential equations has been used to solve the nonlinear coupled system of equations, leading to a staggered product formula solution algorithm. Nonlinear stability issues are discussed and isentropic and isothermal operator splits are formulated. Within the isentropic split, a strong operator split design constraint is introduced, by requiring that the elastic and plastic entropy, as well as the phase-change induced elastic entropy due to the latent heat, remain fixed in the mechanical problem. The formulation of the model has been consistently derived within a thermodynamic framework. The constitutive behavior has been defined by a thermoelastoplastic free energy function, including a thermal multiphase change contribution. Plastic response has been modeled by a J2 temperature dependent model, including plastic hardening and thermal softening. A brief summary of the thermomechanical frictional contact model is included. The numerical model has been implemented into the computational Finite Element code COMET developed by the authors. A numerical assessment of the isentropic and isothermal operator splits, regarding the nonlinear stability behavior, has been performed for weakly and strongly coupled thermomechanical problems. Numerical simulations of solidification processes show the performance of the computational model developed.

  Abstract
  This paper deals with a numerical formulation for coupled thermoplastic problems including phase-change phenomena. The final goal is to get an accurate, efficient and robust [...]

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• Numerical prediction of temperature and density distributions in selective laser sintering processes

  G. Bugeda, M. Cervera, G. Lombera

  Rapid Prototyping Journal (1999). Vol. 5 (1), pp. 21-26

  
  

  Abstract

  A finite element model has been developed for the 3D simulation of the sintering of a single track during a selective laser sintering process (SLS). The model takes into account both the thermal and the sintering phenomena involved in the process. Owing to the continuous movement of the laser beam the model takes also into account the transient nature of the problem. This is transformed into a pseudo‐static one through a transformation of the coordinates system of the equations. Nevertheless, this transformation introduces a convective term into the heat equations that produces instabilities in the solution. These instabilities have been solved by using a stream upwind Petrov Galerkin (SUPG) strategy together with a shock capturing scheme. Finally, a fixed point strategy is used for the solution of the analysis. The model has been tested through the solution of some examples.

  Abstract
  A finite element model has been developed for the 3D simulation of the sintering of a single track during a selective laser sintering process (SLS). The model takes into account [...]

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• Sismología y peligrosidad sísmica

  J. Canas, L. Pujades, E. Banda

  Monograph Series in Earthquake Engineering, editor A. H. Barbat (1994). MIS11, ISBN: 84-87867-49-9

  
  

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• A strain-based plastic viscous-damage model for massive concrete structures

  R. Faria, M. Cervera, J. Oliver

  Int. J. Solids and Structures (1998). Vol. 35 (14), pp. 1533-1558

  
  

  Abstract

  Within the framework of continuum damage mechanics, a new constitutive damage model for massive concrete is presented, mainly intended for the seismic analysis of gravity and arch dams. Consistent with thermodynamic requirements, a straindriven formalism is adopted, improving the algorithmic efficiency as much as required for the analysis of large scale problems to become feasible. Two scalar damage variables are introduced as internal variables, as well as a plastic-strain tensor. An extension to account for the concrete strain-rate dependency, suitable for seismic analysis, is presented at the end. The efficiency of numerical predictions from the constitutive model is illustrated through numerical applications and algorithmic implementation is also detailed.

  Abstract
  Within the framework of continuum damage mechanics, a new constitutive damage model for massive concrete is presented, mainly intended for the seismic analysis of gravity [...]

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• Análise estocástica da resposta sísmica não-linear de estructuras

  A. Cunha

  Monograph Series in Earthquake Engineering, editor A. H. Barbat (1994). MIS09, ISBN: 84-87867-47-2

  
  

  Abstract

  A presente monografia comporta, para além de un capítulo de carácter introdútorio (Capitulo 1), dois capítulos fundamentais (Capítulos 2 e 3), cuja organizaçao e desenvolvimento foram marcados pela preocupaçao de sitematizar adequadamente as mais importantes formulaçoes teóricas que, no âmbito de Dinâmica Estrutural Estocástica, permitem efectuar a análise da resposta aleatória de sitemas não-lineares, complementando cada capítulo com aspectos relativos ao desenvolvimento de progamas de cálculo automático, propositadamente elaborados no sentido de fazer realçar as suas potencialidades à análise da resposta sísmica de estruturas, mediante a apresentação de alguns exemplos julgados elucidativos.

  Abstract
  A presente monografia comporta, para além de un capítulo de carácter introdútorio (Capitulo 1), dois capítulos fundamentais (Capítulos [...]

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• A rate-dependent isotropic damage model for the seismic analysis of concrete dams

  M. Cervera, O. Manzoli, J. Oliver

  Engineering Computations (1996). Vol. 25 (9), pp. 987-1010.

  
  

  Abstract

  In this paper a rate‐dependent isotropic damage model developed for the numerical analysis of concrete dams subjected to seismic excitation is presented. The model is shown to incorporate two features essential for seismic analysis: stiffness degradation and stiffness recovery upon load reversals and strain‐rate sensitivity. The issue of mesh objectivity is addressed using the concept of the ‘characteristic length’ of the fracture zone, to show that both the softening modulus and the fluidity parameter must depend on it to provide consistent results as the computational mesh is refined. Some aspects of the numerical implementation of the model are also treated, to show that the model can be easily incorporated in any standard non‐linear finite element code. The application of the proposed model to the seismic analysis of a large gravity concrete dam shows that the structural response may vary significantly in terms of the development of damage. The inclusion of rate sensitivity is able to reproduce the experimental observation that the tensile peak strength of concrete can be increased up to 50 percent for the range of strain rates that appear in a structural safety analysis of a dam subjected to severe seismic actions.

  Abstract
  In this paper a rate‐dependent isotropic damage model developed for the numerical analysis of concrete dams subjected to seismic excitation is presented. The model is shown [...]

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