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CONTENTS
Volume 3, Number 1, March 2014
 

Abstract
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Key Words
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Address
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Abstract
In this work, we present the theoretical formulation, operator split solution procedure and partitioned software development for the coupled thermomechanical systems. We consider the general case with nonlinear evolution for each sub-system (either mechanical or thermal) with dedicated time integration scheme for each sub-system. We provide the condition that guarantees the stability of such an operator split solution procedure for fully nonlinear evolution of coupled thermomechanical system. We show that the proposed solution procedure can accommodate different evolution time-scale for different sub-systems, and allow for different time steps for the corresponding integration scheme. We also show that such an approach is perfectly suitable for parallel computations. Several numerical simulations are presented in order to illustrate very satisfying performance of the proposed solution procedure and confirm the theoretical speed-up of parallel computations, which follow from the adequate choice of the time step for each sub-problem. This work confirms that one can make the most appropriate selection of the time step with respect to the characteristic time-scale, carry out the separate computations for each sub-system, and then enforce the coupling to preserve the stability of the operator split computations. The software development strategy of direct linking the (existing) codes for each sub-system via Component Template Library (CTL) is shown to be perfectly suitable for the proposed approach.

Key Words
coupled thermomechanical system; operator split procedure; nonlinear stability analysis; multiscale in time; code-coupling via CTL

Address
R. Niekamp, A. Ibrahimbegovic and H.G. Matthies : Technical University Braunschweig, D-38092 Braunschweig, Germany
A. Ibrahimbegovic: Ecole Normale Superieure de Cachan, 94235 Cachan Cedex, France

Abstract
For landfill monitoring and aftercare, long-term prognoses of emission and deformation behaviour are required. Landfills may be considered as heterogeneous porous soil-like structures, in which flow and transport processes of gases and liquids interact with local material degradation and mechanical deformation of the solid skeleton. Therefore, in the framework of continuous porous media mechanics a model is developed that permits the investigation of coupled mechanical, hydraulical and biochemical processes in municipal solid waste landfills.

Key Words
multiphysics; porous media; waste; transport processes; degradation; settlements

Address
Ursula Kowalsky, Sonja Bente and Dieter Dinkler:Institute for Structural Analysis, TU Braunschweig, Beethovenstra

Abstract
Accurate prognoses of the durability of concrete structures require a detailed description of the continuously running aging processes and a consideration of the complete load history. Therefore, in the framework of continuous porous media mechanics a model is developed, which allows a detailed analysis of the most important aging processes of concrete as well as a flexible coupling of different processes. An overview of the prediction model and the balance equations is given. The material dependent model equations, the consequences of coupling different processes and the solution scheme are discussed. In two case studies the aging of concrete due to hydration and chloride penetration are presented, which illustrate the capabilities and the characteristics of the developed model.

Key Words
THCM modeling; porous media; aging of concrete; degradation

Address
Friedhelm Cramer, Ursula Kowalsky and Dieter Dinkler:Institute for Structural Analysis, TU Braunschweig, Beethovenstra

Abstract
The paper deals with a model founded on the physical processes in concrete subject to high temperatures. The model is developed in the framework of continuum damage mechanics and the theory of porous media and is demonstrated on selected structures. The model comprises balance equations for heat transfer, mass transfer of water and vapour, for linear momentum and for reaction. The balance equations are completed by constitutive equations considering the special behaviour of concrete at high temperatures. Furthermore, the limitation and decline of admissible stresses is achieved by using a composed, temperature depending crack surface with a formulation for the damage evolution. Finally, the complete coupled model is applied to several structures and to different concrete in order to determine their influence on the high-temperature-behaviour.

Key Words
concrete; high temperatures; coupled thermo-mechanical-chemical damage

Address
Lars Ostermann and Dieter Dinkler :Institut für Statik, Beethovenstrasse 51, 38106 Braunschweig, Germany

Abstract
In this work we provide the theoretical formulation, discrete approximation and solution algorithm for instability problems combing geometric instability at large displacements and material instability due to softening under combined thermo-mechanical extreme loads. While the proposed approach and its implementation are sufficiently general to apply to vast majority of structural mechanics models, more detailed developments are provided for truss-bar model. Several numerical simulations are presented in order to illustrate a very satisfying performance of the proposed methodology.

Key Words
nonlinear instability; localized failure; large deformations; thermo-mechanical coupling

Address
Van Minh Ngo: École Normale Supérieure, 61 Avenue du Président Wilson, 94230 Cachan, France;
University of Communications and Transport, Civil Engineering, Hanoi, Vietnam
Adnan Ibrahimbegovic:École Normale Supérieure, 61 Avenue du Président Wilson, 94230 Cachan, France
Emina Hajdo:École Normale Supérieure, 61 Avenue du Président Wilson, 94230 Cachan, France;
University of Sarajevo,Civil Engineering, Patriotskelige 30, 71000 Sarajevo, Bosnia and Herzegovina


Abstract
In this paper we present a new model for computing the nonlinear response of reinforced concrete frame systems subjected to extreme thermomechanical loads. The first main feature of the model is its ability to account for both bending and shear failure of the reinforced concrete composites within frame-like model. The second prominent feature concerns the model capability to represent the total degradation of the material properties due to high temperature and the thermal deformations. Several numerical simulations are given to confirm these capabilities and illustrate a very satisfying model performance.

Key Words
thermomechanics failure; timoshenko beam; enhanced finite element

Address
Minh Ngo:École Normale Supérieure, Laboratory of Mechanics and Technology-Cachan, France;
University of Communications and Transport, Department of Civil Engineering, Vietnam
Adnan Ibrahimbegovic :École Normale Supérieure, Laboratory of Mechanics and Technology-Cachan, France
Delphine Brancherie:Université de Technologie de Compiègne, Laboratory Roberval, France

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