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CONTENTS
Volume 7, Number 4, August 2010
 

Abstract
In this work we first review the statistical data on large fires in urban areas, presenting a detailed list of causes of fires, the type of damage to concrete and reinforced concrete structures. We also present the modern experimental approach for studying the fire-resistance of different structural components, along with the role of numerical modeling to provide more detailed information on quantifying the temperature and heat flux fields. In the last part of this work we provide the refined models for assessment of fireinduced damage in structures built of concrete and/or reinforced-concrete. We show that the refined models of this kind are needed to provide a more thorough explanation of damage and to complete the damage assessment and post-fire evaluations.

Key Words
fire induced damage; concrete; structure; fire tests.

Address
Adnan Ibrahimbegovic, Amor Boulkertous and Luc Davenne: Ecole Normale Superieure, LMT-Cachan, Civil Engineering, 61 avenue du president Wilson, 94235 Cachan, France
Medzid Muhasilovic: Unverisity of Ljubljana, Mechanical Engineering, Slovenia
Ahmed Pokrklic: University of Sarajevo, Faculty of Architecture, Bosnia and Herzegovina

Abstract
In this paper, we present a new finite Timoshenko beam element with a model for ultimate load computation of reinforced concrete frames. The proposed model combines the descriptions of the diffuse plastic failure in the beam-column followed by the creation of plastic hinges due to the failure or collapse of the concrete and or the re-bars. A modified multi-scale analysis is performed in order to identify the parameters for stress-resultant-based macro model, which is used to described the behavior of the Timoshenko beam element. The micro-scale is described by using the multi-fiber elements with embedded strain discontinuities in mode 1, which would typically be triggered by bending failure mode. A special attention is paid to the influence of the axial force on the bending moment - rotation response, especially for the columns behavior computation.

Key Words
reinforced concrete frames; macro model; embedded discontinuities.

Address
Ba-Hung Pham, Luc Davenne and Adnan Ibrahimbegovic: Ecole Normale Superieure de Cachan - Laboratoire de Mecanique et Technologie 61, av. du president Wilson, 94235 Cachan cedex, France
Delphine Brancherie: Universite de Technologie de Compiegne - Laboratoire Roberval BP 20529, 60205 Compiegne Cedex, France

Abstract
The paper describes localization of deformation in a bar under tensile loading. The material of the bar is considered as non-linear viscous elastic and the bar consists of two symmetric halves. It is assumed that the model represents behavior of the quasi-brittle viscous material under uniaxial tension with different loading rates. Besides that, the bar could represent uniaxial stress-strain law on a single plane of a microplane material model. Non-linear material property is taken from the microplane material model and it is coupled with the viscous damper producing non-linear Maxwell material model. Mathematically, the problem is described with a system of two partial differential equations with a nonlinear algebraic constraint. In order to obtain solution, the system of differential algebraic equations is transformed into a system of three partial differential equations. System is subjected to loadings of different rate and it is shown that localization occurs only for high loading rates. Mathematically, in such a case two solutions are possible: one without the localization (unstable) and one with the localization (stable one). Furthermore, mass is added to the bar and in that case the problem is described with a system of four differential equations. It is demonstrated that for high enough loading rates, it is the added mass that dominates the response, in contrast to the viscous and elastic material parameters that dominated in the case without mass. This is demonstrated by several numerical examples.

Key Words
softening material; dynamic loading; bifurcation; localization.

Address
Ivica Kožar: Faculty of Civil Engineering, University of Rijeka, Croatia
Joško Ožbolt: Faculty of Civil Engineering, University of Rijeka, Croatia,
Institut fur Werkstoffe im Bauwesen, Universit? Stuttgart, Germany

Abstract
Seismically induced structural damage, as well as any damage caused by a natural catastrophic event, covers a wide area. This suggests to supervise the event consequences by vision tools. This paper reports the evolution from the results obtained by the project RADATT (RApid Damage Assessment Telematics Tool) funded by the European Commission within FP4.The aim was to supply a rapid and reliable damage detector/estimator for an area where a catastrophic event had occurred. Here, a general open-source methodology for the detection and the estimation of the damage caused by natural catastrophes is developed. The suitable available hazard and vulnerability data and satellite pictures covering the area of interest represent the required bits of information for updated telematics tools able to manage it. As a result the global damage is detected by the simple use of open source software. Acase-study to a highly dense agglomerate of buildings is discussed in order to provide the main details of the proposed methodology.

Key Words
catastrophic event; damage detection; GIS; risk assessment; risk management; satellite image

Address
Daniele Bortoluzzi, Fabio Casciati, Lorenzo Elia and Lucia Faravelli: Department of Civil Engineering and Architecture, University of Pavia
Via Ferrata 3, 27100, Pavia, Italy

Abstract
We present a quadrilateral finite element with an embedded crack that can be used to model tensile fracture in two-dimensional concrete solids and the crack growth. The element has kinematics that can represent linear jumps in both normal and tangential displacements along the crack line. The cohesive law in the crack is based on rigid-plasticity with softening. The required material data for the concrete failure analysis are the constants of isotropic elasticity and the mode I softening curve. The results of two well known tests are presented in order to illustrate very satisfying performance of the presented approach to simulate failure of concrete solids.

Key Words
embedded crack; finite element method; 2D solid; concrete.

Address
Jaka Dujc and Boštjan Brank: University of Ljubljana, Faculty of Civil and Geodetic Engineering, Slovenia
Adnan Ibrahimbegovic:Ecole Normale Superieure de Cachan, France
Delphine Brancherie: Universite de Technologie de Compiegne, France

Abstract
Since its invention in the 19th century, Reinforced Concrete (RC) has been widely used in the construction of a lot of different structures, as buildings, bridges, nuclear central plants, or even ships. The details of the mechanical response for this kind of structures depends directly upon the material behavior of each component: concrete and steel, as well as their interaction through the bond-slip, which makes a rigorous engineering analysis of RC structures quite complicated. Consequently, the practical calculation of RC structures is done by adopting a lot of simplifications and hypotheses validated in the elastic range. Nevertheless, as soon as any RC structural element is working in the inelastic range, it is possible to obtain the numerical prediction of its realistic behavior only through the use of non linear analysis. The aim of this work is to develop a new kind of Finite Element: the

Key Words
enhanced solid element; reinforced concrete; x-fem, bond-slip.

Address
Norberto Dominguez and Marco Aurelio Fernandez: Seccion de Estudios de Posgrado e Investigacion (SEPI), ESIA-UZ, Instituto Politecnico Nacional. Av. Juan de Dios Batiz s/n edif. 12, 07738 Mexico D.F., Mexico
Adnan Ibrahimbegovic: Laboratoire de Mecanique et Technologie (LMT), ENS-Cachan/UPMC/CNRS/PRES
Univer Sud Paris 61 Avenue du President Wilson, F-94230 Cachan, France

Abstract
This paper presents the physical formulation of a 1D material model suitable for seismic applications. It is written within the framework of thermodynamics with internal variables that is, especially, very efficient for the phenomenological representation of material behaviors at macroscale: those of the representative elementary volume. The model can reproduce the main characteristics observed for concrete, that is nonsymetric loading rate-dependent (viscoelasticity) behavior with appearance of permanent deformations and local hysteresis (continuum plasticity), stiffness degradation (continuum damage), cracking due to displacement localization (discrete plasticity or damage). The parameters have a clear physical meaning and can thus be easily identified. Although this point is not detailed in the paper, this material model is developed to be implemented in a finite element computer program. Therefore, for the benefit of the robustness of the numerical implementation, (i) linear state equations (no local iteration required) are defined whenever possible and (ii) the conditions in which the presented model can enter the generalized standard materials class . whose elements benefit from good global and local stability properties . are clearly established. To illustrate the capabilities of this model . among them for Earthquake Engineering applications . results of some numerical applications are presented.

Key Words
thermodynamics with internal variables; phenomenological approach; continuum-discrete plasticity and damage models; generalized standard material; earthquake engineering.

Address
Pierre Jehel: LMT-Cachan (ENS Cachan/CNRS/UPMC/PRES UniverSud Paris) 61 av. du President Wilson, 94230 Cachan, France,
Department of Civil Engineering, Ecole Polytechnique de Montreal University of Montreal Campus, P.O. Box 6079, Station CV, Montreal, PQ, Canada H3C 3A7
Luc Davenne and Adnan Ibrahimbegovic: LMT-Cachan (ENS Cachan/CNRS/UPMC/PRES UniverSud Paris) 61 av. du President Wilson, 94230 Cachan, France
Pierre Leger: Dept. of Civil Engineering, Ecole Polytechnique de Montreal University of Montreal Campus,
P.O. Box 6079, Station CV, Montreal, PQ, Canada H3C 3A7

Abstract
From typical stress-axial strain curve and stress-volume strain curve of a concrete under uniaxial compression, the initiation and localization of microcracks within the interior of the specimen can be identified. The occurrence of random microcrack indicates the end of the linear elasticity, and the localization of microcrack implies formation of major crack, which triggers the onset of unstable crack propagation. The interval between initiation and localization of microcracks is characterized by a stable microcrack growth. Based on fracture behavior observed from a uniaxial compressive test of a concrete cylinder, a model has been developed to extract fundamental fracture properties of a concrete, i.e. the equivalent fracture toughness and the size of fracture process zone. The introduction of cracking Poisson

Key Words
concrete, microcrack, stress-strain relation, fracture toughness, uniaxial compression.

Address
Zongjin Li: Dept. of Civil and Environmental Engineering, HongKong University of Science & Technology, Hong Kong, China
Yanhua Zhao: Dept. of Civil Engineering, Dalian University of Technology, Dalian, China


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