References of "Franssen, Jean-Marc"
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See detailSteel hollow columns with an internal profile filled with self-compacting concrete under fire conditions
Chu, Thi Binh; Gernay, Thomas ULg; Dotreppe, Jean-Claude ULg et al

in Proceeding of the Romanian Academy. Series A, Mathematics, Physics, Technical Sciences, Information Science (in press)

A detailed experimental and numerical investigation has been performed on the behavior under fire conditions of concrete filled steel hollow section (CFSHS) columns. In this study the internal ... [more ▼]

A detailed experimental and numerical investigation has been performed on the behavior under fire conditions of concrete filled steel hollow section (CFSHS) columns. In this study the internal reinforcement consists of another profile (tube or H section) being embedded with the concrete, and filling is realized by self-compacting concrete (SCC). Ten columns filled with self-compacting concrete embedding another steel profile have been tested in the Fire Testing Laboratory of the University of Liege, Belgium. Numerical simulations on the thermal and structural behavior of these elements have been made using the non linear finite element software SAFIR developed at the University of Liege. There is a rather good agreement between numerical and experimental results, which can be slightly improved by using the ETC (Explicit Transient Creep) model incorporated in SAFIR. This shows that numerical analyses can predict well the behavior of CFSHS columns under fire conditions. The properties at high temperatures of self-compacting concrete are considered the same as those of ordinary concrete. [less ▲]

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See detailA performance indicator for structures under natural fire
Gernay, Thomas ULg; Franssen, Jean-Marc ULg

in Engineering Structures (2015), 100

Fires in buildings are characterized by a heating phase followed by a cooling phase, yet the effects of the latter on structures are not well covered in the current approaches to structural fire ... [more ▼]

Fires in buildings are characterized by a heating phase followed by a cooling phase, yet the effects of the latter on structures are not well covered in the current approaches to structural fire engineering. Indeed the actual requirement of non-occurrence of structural failure at peak temperature does not guarantee against a delayed failure during or after the cooling phase of a fire, which puts at risk the fire brigades and people proceeding to a building inspection after a fire. Therefore there is an urgent need to better comprehend and characterize the materials and structures behavior under decreasing temperatures. Sensitivity to delayed failure of a structural component depends on its typology and constituting materials. In particular, two structural components with the same Fire Resistance rating (R) under standardized fire may exhibit very distinct behavior under natural fire, one of them being more prone to delayed failure than the other. With the aim of quantifying this effect, a new indicator is proposed that characterizes the performance of structures under natural fire conditions. The paper presents the methodology to derive this new indicator as well as results for different typologies of structural components. Parametric analyses highlight the prime influence of constitutive material and thermal inertia of the element on the post-peak behavior. Used in conjunction with the Fire Resistance rating, it is shown how the new indicator carries additional and significant information for classifying structural systems in terms of their fire performance and propensity to delayed failure. [less ▲]

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See detailCharacteristics and implementation of Hybrid Fire Testing (HFT)
Sauca, Ana ULg; Gernay, Thomas ULg; Robert, Fabienne et al

Conference (2015, June 18)

This presentation is dedicated to real time hybrid testing of building members subjected to the action of fire. It will be shown why, whereas pseudo-dynamic testing is possible in other fields, real time ... [more ▼]

This presentation is dedicated to real time hybrid testing of building members subjected to the action of fire. It will be shown why, whereas pseudo-dynamic testing is possible in other fields, real time hybrid testing is the only possible option for the evaluation of fire performance (except, perhaps, for pure metallic unprotected structures). For some structures subjected to fire, the load bearing mechanism in the physical component is completely modified during the test and this modification can take place within a very short period of time. Because of that, the computational demand can be very challenging if the simulated element is simulated in a fully nonlinear computer model, especially if the thermal problem (temperature distribution in the structure) and the mechanical problem have both to be solved within each time step. In order to avoid these difficulties, a possible solution may be to calculate the stiffness matrix that dictates the reaction of the simulated element on the tested element before the test. This matrix can be constant or vary as a function of the displacements measured at the interface during the test. This procedure is very robust but it also has some shortcomings and limitations. The main topic of this paper is the discussion of the advantages and limitations of this procedure applied to hybrid fire testing. A series of three tests which is now under preparation to be performed in the furnace PROMETHEE of CERIB, in France, will also be described in this respect. Preliminary results will be presented if some or all of the tests have been performed at the date of the conference. [less ▲]

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See detailA plastic-damage model for concrete in fire: Applications in structural fire engineering
Gernay, Thomas ULg; Franssen, Jean-Marc ULg

in Fire Safety Journal (2015), 71

The research aims at developing a new multiaxial constitutive model for concrete in the fire situation. In addition to validity at the material level, a crucial feature of a constitutive model is the ... [more ▼]

The research aims at developing a new multiaxial constitutive model for concrete in the fire situation. In addition to validity at the material level, a crucial feature of a constitutive model is the applicability at the structural level; yet for concrete in fire there remains a serious lack of models combining reliability and robustness. The theoretical aspects and validation of the new model, which rely on a plastic-damage formulation, have been the subject of a former publication; they are briefly summarized here. This paper explores the capabilities of the concrete model for being used in a performance-based structural fire engineering framework. Several examples of numerical simulations by non-linear finite element method are discussed, with emphasis on practical applications that are demanding for the material model. In particular, it is shown that the simulations using the new concrete model succeed in capturing, at ambient temperature, the crack pattern in a plain concrete specimen and the influence of the loading path on reinforced concrete (RC) slabs. At high temperature, the presented applications include a RC slab subjected to furnace fire and a large-scale composite steel–concrete structure subjected to natural fire. In the numerical analyses, no parameter calibration was required on the particular concrete type, except for the uniaxial strengths and tensile crack energy which are to be defined case-by-case. The results illustrate the reliability and numerical robustness of the model. Also, they suggest that satisfactory prediction of structural behavior in fire can be obtained when no additional data is available on the specific properties of the particular concrete mix that is used in the project, as is often the case in practice, by using standard values of parameters. [less ▲]

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See detailSimulation of 5 fire tests on reinforced concrete columns using SAFIR
Gernay, Thomas ULg; Franssen, Jean-Marc ULg

Report (2015)

This report presents the results of numerical simulations on five tests conducted on reinforced concrete columns in fire. The data for the studied RC columns have been provided by the CERIB in the ... [more ▼]

This report presents the results of numerical simulations on five tests conducted on reinforced concrete columns in fire. The data for the studied RC columns have been provided by the CERIB in the document “CEN-TC250-SC2-WG1-TG5_N0043_Annex_C_examples_Jesper_Jensen”. This study is part of the research project CEN-TC250-SC2-WG1-TG5 on the revision of EN1992-1-2, which focuses on the columns. The numerical software that is used for the simulations is the non-linear finite element software SAFIR, version 2013a0. [less ▲]

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See detailLoadbearing capacity criteria in fire resistance testing
Dumont, Fabien ULg; Wellens, Eric ULg; Franssen, Jean-Marc ULg

Report (2015)

Experimental testing may be used to demonstrate the fire resistance of building construction elements. In order to allow comparing the results of tests made in different laboratories on various types of ... [more ▼]

Experimental testing may be used to demonstrate the fire resistance of building construction elements. In order to allow comparing the results of tests made in different laboratories on various types of elements, the tests have to be performed under well-defined standardised conditions. Such standards define the heating and loading conditions, but also the performance criteria that have to be applied to measure the fire resistance duration. In Europe, the procedure that leads to the classification of building construction elements with regards to fire resistance involves a two level process. In the first stage, one or several tests are performed by a laboratory that must have accreditation according to ISO 17025, and one test report is issued for each test. Thereafter, a competent body will compile the necessary test reports and issue a classification report, the results of which can be used by the different stakeholders of the construction process, e.g. by authorities having jurisdiction. For the loadbearing performance, it appears that different logical combinations of the criteria are considered in the test standard and in the classification standard, leading to a inextricable situation. This situation has to be fixed in order to lead to a complete credible and applicable system. In order to provide scientific evidence about the consequences of adopting one or the other of both loadbearing definitions, the results of 46 tests performed in the fire resistance lab of the University of Liege in the recent years are analysed in this paper. [less ▲]

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See detailStabilité des Constructions
Denoël, Vincent ULg; Franssen, Jean-Marc ULg

Learning material (2015)

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See detailRevision of the tabulated methods of EN1992-1-2 for concrete columns in fire - Part 2
Gernay, Thomas ULg; Franssen, Jean-Marc ULg

Report (2014)

This report presents the results of numerical simulations conducted on reinforced concrete columns in fire for comparison of the computed fire resistance with the fire resistance obtained by the tabulated ... [more ▼]

This report presents the results of numerical simulations conducted on reinforced concrete columns in fire for comparison of the computed fire resistance with the fire resistance obtained by the tabulated methods of EN1992-1-2. The data for the studied RC columns have been provided by the CERIB in the document “CENTC250-SC2-WG1-TG5_N0038_Column_Calculation”. This study is part of the research project CEN-TC250-SC2-WG1-TG5. The objective is to assess the validity of and possibly to revise the tabulated methods of EN1992-1-2. The numerical software that is used for the simulations is the non-linear finite element software SAFIR, version 2013a0. [less ▲]

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See detailRevision of the tabulated methods of EN1992-1-2 for concrete columns in fire - Part 1
Gernay, Thomas ULg; Franssen, Jean-Marc ULg

Report (2014)

This report presents the results of numerical simulations conducted on reinforced concrete columns in fire for comparison of the computed fire resistance with the fire resistance obtained by the tabulated ... [more ▼]

This report presents the results of numerical simulations conducted on reinforced concrete columns in fire for comparison of the computed fire resistance with the fire resistance obtained by the tabulated methods of EN1992-1-2. The data for the studied RC columns have been provided by the CERIB in the document “CENTC250-SC2-WG1-TG5_N0037_Annex_C_studies_Jesper_Jensen”. This study is part of the research project CEN-TC250-SC2-WG1-TG5. The objective is to assess the validity of and possibly to revise the tabulated methods of EN1992-1-2. The numerical software that is used for the simulations is the non-linear finite element software SAFIR, version 2013a0. [less ▲]

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See detailExperimental tests and numerical modelling on eight slender steel columns under increasing temperatures
Franssen, Jean-Marc ULg; Zhao, Bin; Gernay, Thomas ULg

in Li, G.Q.; Jiang, S.C.; Chen, Suwen (Eds.) et al Progress on Safety of Structures in Fire (2014, June 11)

In order to fill the lack of knowledge about slender elements behavior at elevated temperatures,, a European research project called FIDESC4 has been funded by the RFCS. This project involves experimental ... [more ▼]

In order to fill the lack of knowledge about slender elements behavior at elevated temperatures,, a European research project called FIDESC4 has been funded by the RFCS. This project involves experimental testing, parametric numerical analyses and development of simple design rules. The present paper reports the characteristics and the results of the FIDESC4 experimental test campaign performed at the University of Liege on slender steel columns at elevated temperatures. A total of eight columns have been tested, all of them with I shape section. Six columns were made of welded sections (some prismatic and some tapered members) and two columns were with hot rolled sections. The nominal length of the columns was 3 meters with the whole length being heated. The strength of the material (webs and flanges) was measured on sample before the tests. The order of magnitude of the initial geometrical imperfections was recorded. The columns were not restrained against longitudinal thermal elongation. The supports at the ends were cylindrical thus inducing a restrain against rotation in one plane while allowing rotation in the other plane. The allowed direction of rotation was chosen in each test to induce buckling around the strong or the weak axis. The load was applied at ambient temperature and maintained for a period of 15 minutes after which the temperature was increased under constant load. The load was applied concentrically on some tests and with an eccentricity in other tests. The load eccentricity was either applied at both ends, leading to constant bending moment distribution along the length, or at one end only, leading to a triangular bending moment distribution. Heating was applied by electrical resistances enclosed in ceramic pads. The columns and the ceramic pads were wrapped in ceramic wool insulating material. This technique was preferred to gas heating in a standard test furnace because it allows applying a slower and better controlled heating rate and thus obtaining a more uniform temperature distribution in the member. It is also easier to measured lateral displacements of the column. Preliminary blank tests were performed on unloaded specimen in order to determine the heating range to be used later on the loaded columns. The paper will also report on a modification of the heating technique that was applied and improved significantly the uniformity in the temperature distribution. Numerical simulations were performed before the tests using shell elements of the software SAFIR and assumed values of the material properties in order to predict the failure modes. It was essentially crucial to determine whether lateral supports at intermediate levels should be provided in order to ensure failure in the desired direction. Experience showed that the failure modes developed as predicted by the numerical simulations. Besides a thorough description of the experiments, the paper will also present the obtained results in terms of failure mode, ultimate temperature and evolution of longitudinal and transverse displacement. Some information will also be given about the level of detail that has to be used in the numerical model in order to get accurate results at a reasonable price. [less ▲]

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See detailEffective stress method to be used in beam finite elements to take local instabilities into account
Franssen, Jean-Marc ULg; Cowez, Baptiste; Gernay, Thomas ULg

in Proceedings of the 11th IAFSS Symposium (2014, February)

In the fire situation, Bernoulli beam finite elements are the workhorse used in numerical calculation model for simulating the behaviour of the structure. Such finite elements treat all sections as class ... [more ▼]

In the fire situation, Bernoulli beam finite elements are the workhorse used in numerical calculation model for simulating the behaviour of the structure. Such finite elements treat all sections as class 1 (stocky) sections whatever the slenderness of the plates that make the section, allowing the development of a full plastic stress distribution in the section which leads to complete plastic redistribution along the members in the structure. This type of element is thus not adapted for modeling structures that contain slender sections of class 2, 3 or 4. This document presents a new approach to take into account local instabilities in slender sections using beam finite elements. The new approach is based on an effective constitutive law of steel. The effective law is not symmetrical with respect to tension and compression because, in tension, the stress-strain relationship is not modified whereas, in compression, the stress-strain relationship is modified. [less ▲]

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See detailAre Simple Calculation Models always on the Safe Side?
Franssen, Jean-Marc ULg

in Schaumann, Peter (Ed.) Festschrift Peter Schaumann (2014)

This paper examines the question whether simple calculation models are always on the safe side compared to advanced calculation models. This question is examined for the shadow effect, for the contact ... [more ▼]

This paper examines the question whether simple calculation models are always on the safe side compared to advanced calculation models. This question is examined for the shadow effect, for the contact between steel and concrete in composite steel-concrete floors, for the buckling curves of steel sections and, finally, for the factors κ1 and κ2 applied to the bending resistance of steel beams. [less ▲]

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See detailA multiaxial constitutive model for concrete in the fire situation: Theoretical formulation.
Gernay, Thomas ULg; Millard, Alain; Franssen, Jean-Marc ULg

in International Journal of Solids and Structures (2013), 50(22-23), 3659-3673

This paper aims to develop a multiaxial concrete model for implementation in finite element softwares dedicated to the analysis of structures in fire. The need for proper concrete model remains a ... [more ▼]

This paper aims to develop a multiaxial concrete model for implementation in finite element softwares dedicated to the analysis of structures in fire. The need for proper concrete model remains a challenging task in structural fire engineering because of the complexity of the concrete mechanical behavior characterization and the severe requirements for the material models raised by the development of performance-based design. A fully threedimensional model is developed based on the combination of elastoplasticity and damage theories. The state of damage in concrete, assumed isotropic, is modeled by means of a fourth order damage tensor to capture the unilateral effect. The concrete model comprises a limited number of parameters that can be identified by three simple tests at ambient temperature. At high temperatures, a generic transient creep model is included to take into account explicitly the effect of transient creep strain. The numerical implementation of the concrete model in a finite element software is presented and a series of numerical simulations are conducted for validation. The concrete behavior is accurately captured in a large range of temperature and stress states. A limitation appears when modeling the concrete post-peak behavior in highly confined stress states, due to the coupling assumption between damage and plasticity, but the considered levels of triaxial confinement are unusual stress states in structural concrete. [less ▲]

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See detailFIRE TESTING OF HIGH-STRENGTH STEEL CIRCULAR COLUMNS
Tondini, Nicola; Van Long, Hoang; Demonceau, Jean-François ULg et al

Conference (2013, September 30)

This paper presents an experimental-numerical study on the behaviour of High Strength Steel (HSS) columns at elevated temperature, both on Circular Hollow Sections (CHS) and on a Concrete Filled Tube (CFT ... [more ▼]

This paper presents an experimental-numerical study on the behaviour of High Strength Steel (HSS) columns at elevated temperature, both on Circular Hollow Sections (CHS) and on a Concrete Filled Tube (CFT). The measured yield strength of the circular sections was in the order of 820 MPa. In detail, three HSS CHS and a HSS CFT were tested under the standard ISO fire with constant eccentric compression load. The evolution of temperature and defor-mation patterns were measured by means of a comprehensive instrumentation made of ther-mocouples and displacement transducers. Numerical analyses were performed and compared with experimental data by employing stress-strain relationships of carbon steel at elevated temperatures provided by EN1993-1-2 associated with two different sets of reduction factors: i) those provided by EN1993-1-2 valid up to S460 steel grades; and ii) those proposed in the literature and based on tests on HSS. [less ▲]

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See detailResistencia al fuego de armaduras de acero inoxidable
Franssen, Jean-Marc ULg; Gernay, Thomas ULg

in Bastidas, David M; Medina Sanchez, Eduardo (Eds.) Armaduras de Acero Inoxidable (2013)

Un incendio constituye un riesgo por dos razones, la toxicidad del aire y las altas temperaturas. Dependiendo de si se produce al aire libre o en un recinto cerrado la magnitud del peligro varía ... [more ▼]

Un incendio constituye un riesgo por dos razones, la toxicidad del aire y las altas temperaturas. Dependiendo de si se produce al aire libre o en un recinto cerrado la magnitud del peligro varía notablemente. En el exterior, es poco probable superar los 700ºC, sin embargo, en el interior la temperatura puede llegar a ser mucho más elevada. Infraestructuras críticas son los túneles, además de por ser recintos cerrados, por la naturaleza de los materiales inflamables que albergan. El diseño y la resistencia de los materiales son aspectos claves para garantizar un tiempo suficiente hasta el colapso. Los efectos en las estructuras de hormigón armado empiezan en el propio comportamiento de los materiales. El hormigón pierde menos capacidad a altas temperaturas que el acero, por lo tanto, utilizar aceros con mejores propiedades a altas temperaturas como los inoxidables aumentan las prestaciones del conjunto de la estructura. En este capítulo se describen las características térmicas del acero inoxidable y cómo varían sus características mecánicas en función de la temperatura. Por medio de simulaciones informáticas (software SAFIR de la Universidad de Lieja) se ha realizado un análisis térmico de armaduras de acero inoxidable de diferentes tipos y al carbono, embebidas en hormigón con distintos recubrimientos, en sección de columna y de viga. Finalmente, se ha realizado un análisis estructural de dichos elementos sometidos a diferentes cargas en puntos temporales distintos en condiciones de fuego. [less ▲]

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See detailIMPLEMENTATION OF A WEAK COUPLING APPROACH BETWEEN A CFD AND AN FE SOFTWARE FOR FIRES IN COMPARTMENT
Tondini, Nicola; Franssen, Jean-Marc ULg

in Idelsohn, S; Papadrakakis, M; Schrefler, B (Eds.) V International Conference on Computational Methods for Coupled Problems in Science and Engineering (2013, June 17)

The paper presents the assumptions and the issues that arise when developing an integrated modelling methodology between a Computational Fluid Dynamics (CFD) software applied to compartment fires and a ... [more ▼]

The paper presents the assumptions and the issues that arise when developing an integrated modelling methodology between a Computational Fluid Dynamics (CFD) software applied to compartment fires and a Finite Element (FE) software applied to structural systems subjected to fire. In particular, a weak coupling approach used to simulate a fire exposed structure by modelling the fire development in the compartment, the heat penetration in the structure and the mechanical response is described. The advantages and the disadvantages of such a technique are highlighted compared to a full coupling that conversely takes into account all mutual interactions. The favourable aspect of computing the thermal response of the structure in the FE model in order to avoid modelling the structure in the CFD model is underlined, namely a sensitive reduction of computational demand. Finally, the study is enriched by an application of this methodology that concerns the simulation of a pool fire in an open compartment the results of which are compared with those obtained by employing the simplified Hasemi model included in the Eurocodes. [less ▲]

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See detailNumerical simulations in support of fire resistance tests
Franssen, Jean-Marc ULg

Conference given outside the academic context (2013)

This paper presesnts how non linear numerical simulations can be used as a tool to support experimental tests made to determine the fire resistance of building structures. Numerical simulations have been ... [more ▼]

This paper presesnts how non linear numerical simulations can be used as a tool to support experimental tests made to determine the fire resistance of building structures. Numerical simulations have been made to calculate precisely the flexibility of the loading frame, to verify that no undesirable failure mode can develop in a test to be performed, to choose the load to be applied in order to obtain a desired failure temperature and to estimate the influence of observed non uniform temperature distribution. [less ▲]

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