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See detailTESTS FOR DEFINING A STANDARDISED UNIFORMLY DISTRIBUTED FUEL ARRANGEMENT
Gamba, Antonio ULiege; Franssen, Jean-Marc ULiege

Conference (2018, November 20)

This Powepoint presentation gives the main features of the results obtained by ULiege for experimental tests of fire propagation in uniformly distributed cellulosic fire load.

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See detailRFCS TRAFIR
Charlier, Marion; Franssen, Jean-Marc ULiege; Gamba, Antonio ULiege

Diverse speeche and writing (2018)

This Powepoint presentation gives the main features of the RFCS project TRAFIR as well as the first results obtained by ULiege for experimental tests of fire propagation in uniformly distributed ... [more ▼]

This Powepoint presentation gives the main features of the RFCS project TRAFIR as well as the first results obtained by ULiege for experimental tests of fire propagation in uniformly distributed cellulosic fire load. [less ▲]

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See detailSiF 2018 : 10th INTERNATIONAL CONFERENCE ON STRUCTURES IN FIRE
Nadjai, Ali; Ali, Faris; Franssen, Jean-Marc ULiege et al

Book published by Ulster University (2018)

Proceedings of the conference "Structures in Fire"of 2018. It contains 125 papers.

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See detailA PI-controller for hybrid fire testing in a non-linear environment
Mergny, Elke ULiege; Drion, Guillaume ULiege; Gernay, Thomas ULiege et al

in 10th International on structures in fire (2018, June 06)

Hybrid Fire Testing (HFT) is an innovative testing methodology: it improves the existing experimental method by updating continuously the boundary conditions at the ends of a tested specimen. However, HFT ... [more ▼]

Hybrid Fire Testing (HFT) is an innovative testing methodology: it improves the existing experimental method by updating continuously the boundary conditions at the ends of a tested specimen. However, HFT methodologies are still in their infancy and, despite several previous applications, a rigorous framework for formulating the general problem is still lacking. To address this need, this paper proposes a new framework based on linear control system theory. Adoption of this robust theory to HFT allows deriving the general state equations and stability conditions of the problem. It is shown that the use of a P-controller leads to a stable process and that the conditions of stability can be formally expressed. However, the P-controller presents a major drawback, namely an inability to adapt to changes of stiffness in the system. A PI-controller is developed to overcome these limitations, and the corresponding state equations are established. A virtual HFT (using FEM) is performed on a 2D steel frame to compare the two different controllers. The results show that a PI-controller is more efficient in reproducing the global behaviour of the frame. The proposed methodology is versatile and can be used when the surrounding structure is non-linear, including when it is also subjected to fire. [less ▲]

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See detailDiscussion on a systematic approach to validation of software for structures in fire
Romeiro Ferreira, Joao Daniel ULiege; Gernay, Thomas; Franssen, Jean-Marc ULiege

Scientific conference (2018, June 06)

A validation exercise has been performed for the thermo-mechanical software SAFIR® based on a dual approach. First, the examples proposed in the German National Annex of EN 1992-1-2 have been calculated ... [more ▼]

A validation exercise has been performed for the thermo-mechanical software SAFIR® based on a dual approach. First, the examples proposed in the German National Annex of EN 1992-1-2 have been calculated with SAFIR and, second, the references to SAFIR found in scientific publications have been analysed with respect to the level of accuracy estimated by the authors for the results of SAFIR. The aim of this paper is not to present the detailed results of this validation exercise (which are published in open access reports). The focus is more on a critical analysis of the examples presented in the German National Annex which indeed paved the way to a systematic approach to validation of SiF software but could be improved, namely by including sensitivity analyses on the discretisation, a better description of some input data particularly in the material models, a presentation of the means used to obtain some reference results and a clear definition of the failure criteria to be used for determining fire resistance times. Furthermore, extensive analysis of the literature showed that the wide field of application of a typical SiF software requires an extension of the domain covered by the standard on concrete structures. [less ▲]

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See detailEffect of upgrading concrete strength class on fire performance of reinforced concrete columns
Gernay, Thomas ULiege; Peric, Vlado; Mihaylov, Boyan ULiege et al

in Gillie, Martin; Wang, Yong (Eds.) Proceedings of ASFE 2017 Conference (2018)

High strength concrete (HSC) provides several advantages over normal strength concrete (NSC) and is being used in multi-story buildings for reducing the dimensions of the columns sections and increasing ... [more ▼]

High strength concrete (HSC) provides several advantages over normal strength concrete (NSC) and is being used in multi-story buildings for reducing the dimensions of the columns sections and increasing the net marketable area. However, upgrading of concrete strength class in a building may affect the fire performance, due to higher rates of strength loss with temperature and higher susceptibility to spalling of HSC compared with NSC. Reduction of columns sections also leads to increased member slenderness and faster temperature increase in the section core. These detrimental effects are well known, but their impact on fire performance of structures has not been established in terms of comparative advantage between NSC and HSC. In other words, it is not clear whether the consideration of fire resistance limits the opportunities for use of HSC for reducing the dimensions of columns sections in multi-story buildings. This research aims to address this question by comparing the fire behaviour of reinforced concrete columns made of NSC and HSC using nonlinear finite element modelling. The evolution of load bearing capacity of the columns is established as a function of the fire exposure duration. A 15-story car park structure is adopted as a case study with alternative designs for the columns based on strength classes ranging from C30 to C90. Results show that, although the replacement of NSC by HSC accelerates the reduction rate of columns capacity under fire, the columns generally have significant reserves in resistance leading to sufficient fire resistance. This study gives an insight into the impact of replacing stocky sections in NSC by more slender sections in HSC on fire resistance rating for multi-story structures. [less ▲]

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See detailHybrid Fire Testing: Discussion on stability and implementation of a new method in a virtual environment
Sauca, Ana ULiege; Gernay, Thomas ULiege; Robert, Fabienne et al

in Journal of Structural Fire Engineering (2018)

Purpose – The purpose of this paper is to propose a method for Hybrid Fire Testing (HFT) which is unconditionally stable, ensures equilibrium and compatibility at the interface and captures the global ... [more ▼]

Purpose – The purpose of this paper is to propose a method for Hybrid Fire Testing (HFT) which is unconditionally stable, ensures equilibrium and compatibility at the interface and captures the global behavior of the analyzed structure. HFT is a technique that allows assessing experimentally the fire performance of a structural element under real boundary conditions that capture the effect of the surrounding structure. Design/methodology/approach – The paper starts with the analysis of the method used in the few previous HFT. Based on the analytical study of a simple one degree-of-freedom elastic system, it is shown that this previous method is fundamentally unstable in certain configurations that cannot be easily predicted in advance. Therefore, a new method is introduced to overcome the stability problem. The method is applied in a virtual hybrid test on a 2D reinforced concrete beam part of a moment resisting frame. Findings – It is shown through analytical developments and applicative examples that the stability of the method used in previous HFT depends on the stiffness ratio between the two substructures. The method is unstable when implemented in force control on a physical substructure that is less stiff than the surrounding structure. Conversely, the method is unstable when implemented in displacement control on a physical substructure stiffer than the remainder. In multi degrees-of-freedom tests where the temperature will affect the stiffness of the elements, it is generally not possible to ensure continuous stability throughout the test using this former method. Therefore, a new method is proposed where the stability is not dependent on the stiffness ratio between the two substructures. Application of the new method in a virtual HFT proved to be stable, to ensure compatibility and equilibrium at the interface and to reproduce accurately the global structural behavior. Originality/value – The paper provides a method to perform Hybrid Fire Tests which overcomes the stability problem lying in the former method. The efficiency of the new method is demonstrated in a virtual HFT with 3 degrees-of-freedom at the interface, the next step being its implementation in a real (laboratory) hybrid test. [less ▲]

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See detailCfd analyses used to evaluate the influence of compartment geometry on the possibility of development of a travelling fire
Charlier, Marion; Gamba, Antonio ULiege; Dai, Xu et al

in Structures in Fire (Proceedings of the 10th International Conference) (2018)

The response of structures exposed to fire is highly dependent on the type of fire that occurs, which is in turn very dependent on the compartment geometry. In the frame of the European RFCS TRAFIR ... [more ▼]

The response of structures exposed to fire is highly dependent on the type of fire that occurs, which is in turn very dependent on the compartment geometry. In the frame of the European RFCS TRAFIR project, CFD simulations using FDS software were carried out to analyse the influence of compartment geometry and the interaction with representative fuel loads to explore the conditions leading to the development of a travelling fire. The influence observed of ceiling height, crib spacing, and opening geometry in controlling spread rates tend to confirm the possibility to predict the occurrence or not of travelling fire. In a subsequent step, the radiative intensities and gas temperatures calculated by FDS have been used by SAFIR® to calculate the temperatures in steel structural elements located in the compartment and the structural behavior of a frame made of these elements. [less ▲]

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See detailAN EQUIVALENT STRESS METHOD FOR CONSIDERING LOCAL BUCKLING IN BEAM FINITE ELEMENTS IN THE FIRE SITUATION
Maraveas, Chrysanthos ULiege; Gernay, Thomas ULiege; Franssen, Jean-Marc ULiege

in Proceedings of SiF 2018 (2018)

The use of slender steel sections has increased in recent years because they provide excellent strength to weight ratio. Yet, a major issue with slender sections is local buckling in compression zones ... [more ▼]

The use of slender steel sections has increased in recent years because they provide excellent strength to weight ratio. Yet, a major issue with slender sections is local buckling in compression zones. Several researchers have proposed design methods at elevated temperatures based on the effective width approach to calculate the capacity of the plates that compose these steel members, but this approach is not easily compatible with the implementation and use in Bernoulli beam elements. Another approach is the development of a stress based model, i.e. an “effective” constitutive law of steel. This approach was proposed previously by Liege University researchers for slender steel members exposed to high temperatures, and implemented within the framework of fiber type Bernoulli beam elements; however it was giving overly conservative results. This paper presents an improved temperature-dependent constitutive model for steel that accounts for local instabilities using the stress based method. The improved model is derived from refined plate analysis methodology and implemented in the SAFIR finite element analysis software. Validation shows good agreement against experimental and shell element analysis results. [less ▲]

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See detailValidation of SAFIR through DIN EN 1992-1-2 NA: Comparison of the results for the examples presented in Annex CC
Romeiro Ferreira, Joao Daniel ULiege; Franssen, Jean-Marc ULiege; Gernay, Thomas ULiege et al

Report (2017)

Annex CC of DIN EN 1992-1-2 NA presents a series of cases that allow benchmarking software tools aimed at the design of structures in a fire situation. With the goal of providing a validation document for ... [more ▼]

Annex CC of DIN EN 1992-1-2 NA presents a series of cases that allow benchmarking software tools aimed at the design of structures in a fire situation. With the goal of providing a validation document for the finite element code SAFIR [1], a comparison of the reference results for the cases presented in the Annex CC with the results obtained by SAFIR has been carried out and is presented in this document. The validation typically consists in a comparison between the value of a result (temperature, displacement or others) obtained by SAFIR and the value given as a reference and supposed to be the « true » result. The value obtained must fall in the interval stipulated by the document. [less ▲]

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See detailTHIN-WALLED STEEL MEMBERS AT ELEVATED TEMPERATURES CONSIDERING LOCAL IMPERFECTIONS: NUMERICAL SIMULATION OF ISOLATED PLATES
Maraveas, Chrysanthos ULiege; Gernay, Thomas ULiege; Franssen, Jean-Marc ULiege

Scientific conference (2017, October 06)

The local buckling capacity of fire exposed thin-walled steel cross sections is affected by the reduction in strength and stiffness due to elevated temperatures and the amplitude of the initial local ... [more ▼]

The local buckling capacity of fire exposed thin-walled steel cross sections is affected by the reduction in strength and stiffness due to elevated temperatures and the amplitude of the initial local imperfections. A usual method to estimate this capacity is the simulation of isolated plates (web: four sides simply supported plate, flange: three sides simply supported plate) that are subjected to in-plane compression until instability is observed. Several researchers have proposed design methods to calculate the capacity of these steel members at elevated temperatures based on isolated plate analysis, but they used different methodologies. This variability in hypotheses happens because there is no clear provision defining the numerical modeling procedure for fire design of steel plates in the codes (European or US). The paper proposes a methodology for finite element simulation of thin plates at elevated temperatures and its governing factors (amplitude of initial local imperfections, number of half-wave geometry of local imperfections, plate geometry (sides ratio a/b)). [less ▲]

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See detailBuckling of steel plates at elevated temperatures: Theory of perfect plates vs finite element analysis
Maraveas, Chrysanthos ULiege; Gernay, Thomas ULiege; Franssen, Jean-Marc ULiege

in Proceedings of CONFAB'17 Conference (2017, September 11)

The local buckling capacity of fire exposed thin-walled steel cross sections is affected by the reduction in strength and stiffness due to elevated temperatures and the amplitude of the initial local ... [more ▼]

The local buckling capacity of fire exposed thin-walled steel cross sections is affected by the reduction in strength and stiffness due to elevated temperatures and the amplitude of the initial local imperfections. Several researchers have proposed design methods to calculate the capacity of the plates (i.e. web and flanges) that compose these steel members at elevated temperatures, but they used different shapes of steel plates (sides ratio a/b) and different amplitudes of local imperfections. This variability in hypotheses happens because there is no clear provision defining the numerical modeling procedure for fire design of steel plates in the codes (European or US). According to the theory of perfect plates, the critical load depends of the shape of the rectangular plate (e.g. the sides ratio a/b) and the corresponding buckling mode (number of half waves), the boundary and the loading conditions. This paper reviews the existing code provisions and compares the existing design models and their assumptions for thin-walled steel cross sections. Elements of the theory of perfect plates are presented. Parametric finite element analyses are then conducted on isolated steel plates at elevated temperatures to investigate the effect of the plate shape (a/b ratio) and imperfections (amplitude and number of half wave lengths). From the analysis, the governing parameter will be estimated (a/b vs imperfections) for simulation of isolated flanges and webs. Finally, recommendations for the numerical modeling of steel plates at elevated temperatures are proposed. [less ▲]

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See detailA method for hybrid fire testing: Development, implementation and numerical application
Sauca, Ana ULiege; Mergny, Elke ULiege; Gernay, Thomas ULiege et al

in Gillie, Martin; Wang, Yong (Eds.) Proceedings of ASFE 2017 Conference (2017, September 08)

Hybrid Fire Testing (HFT) is a technique that allows assessing experimentally the fire performance of a structural element under real boundary conditions that capture the effect of the surrounding ... [more ▼]

Hybrid Fire Testing (HFT) is a technique that allows assessing experimentally the fire performance of a structural element under real boundary conditions that capture the effect of the surrounding structure. To enable HFT, there is a need for a method that is unconditionally stable, ensures equilibrium and compatibility at the interface and captures the global behaviour of the analysed structure. A few attempts at conducting HFT have been described in the literature, but it can be shown, based on the analytical study of a simple one degree-of-freedom elastic system, that the considered method was fundamentally unstable in certain configurations which depend on the relative stiffness between the two substructures, but which cannot be easily predicted in advance. In this paper, a new method is introduced to overcome the stability problem and it is shown through analytical developments and applicative examples that the stability of the new method does not depend on the stiffness ratio between the two substructures. The new method is applied in a virtual hybrid test on a 2D reinforced concrete beam part of a moment resisting frame, showing that stability, equilibrium and compatibility are ensured on the considered multiple degree-of-freedom system. Besides, the virtual HFT succeeds in reproducing the global behaviour of the analysed structure. The method development and implementation in a virtual (numerical) setting is described, the next step being its implementation in a real (laboratory) hybrid test. [less ▲]

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See detailSensitivity of elevated temperature load carrying capacity of thin-walled steel members to local imperfections
Maraveas, Chrysanthos ULiege; Gernay, Thomas ULiege; Franssen, Jean-Marc ULiege

in Gillie, Martin; Wang, Yong (Eds.) Proceedings of ASFE 2017 Conference (2017, September 07)

The local buckling capacity of fire exposed thin-walled steel cross sections is affected by the reduction in strength and stiffness due to elevated temperatures and by the amplitude of the initial local ... [more ▼]

The local buckling capacity of fire exposed thin-walled steel cross sections is affected by the reduction in strength and stiffness due to elevated temperatures and by the amplitude of the initial local imperfections. Several researchers have proposed design methods to calculate the capacity of these steel members at elevated temperatures, but they used different methodologies and different amplitude of local imperfections in the extensive numerical analyses that are typically at the base of these methods. This variability in hypotheses happens because there is no clear provision defining the local imperfection amplitude for fire design in the codes (European or US). EN 1993-1-5 proposes amplitude values of local imperfections for ambient temperature design, while EN 1090-2 defines a -different- maximum allowed size of fabrication tolerance during production. Meanwhile, other sizes of local imperfections have also been proposed in the literature, with values different than those from EN 1993-1-5 and EN 1090-2. This paper reviews the existing code provisions and compares the existing design models and their assumptions for thin-walled steel cross sections. Finite element analyses are then conducted on isolated steel plates at elevated temperatures to investigate the effect of local imperfections. Finally, specific amplitude of local imperfections is proposed for fire design of thin-walled steel members. [less ▲]

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See detailModeling structures in fire with SAFIR®: Theoretical background and capabilities
Franssen, Jean-Marc ULiege; Gernay, Thomas ULiege

in Journal of Structural Fire Engineering (2017), 8(3), 300-323

Purpose: This paper describes the theoretical background and main hypotheses at the basis of SAFIR®, a nonlinear finite element software for modeling structures in fire. The paper also explains how to use ... [more ▼]

Purpose: This paper describes the theoretical background and main hypotheses at the basis of SAFIR®, a nonlinear finite element software for modeling structures in fire. The paper also explains how to use the software at its full extent. The discussed numerical modeling principles can be applied with other similar software. Approach: Following a general overview of the organization of the software, the thermal analysis part is explained, with the basic equations and the different possibilities to apply thermal boundary conditions (compartment fire, localized fire, etc.). Next, the mechanical analysis part is detailed, including the time integration procedures and the different types of finite elements: beam, truss, shell, spring and solid. Finally, the material laws are described. The software capabilities and limitations are discussed throughout the paper. Findings: By accommodating multiple types of finite elements and materials, by allowing the user to consider virtually any section type and to input the fire attack in multiple forms, the software SAFIR® is a comprehensive tool for investigating the behavior of structures in the fire situation. Meanwhile, being developed exclusively for its well-defined field of application, it remains relatively easy to use. Value: The paper will improve the knowledge of readers (researchers, designers and authorities) about numerical modeling used in structural fire engineering in general and the capabilities of a particular software largely used in the fire engineering community. [less ▲]

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See detailHybrid Fire Testing: A new approach for fire labs
Sauca, Ana ULiege; Gernay, Thomas ULiege; Mergny, Elke ULiege et al

Poster (2017, May 02)

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See detailSAFIR: a software for modeling structures in fire
Franssen, Jean-Marc ULiege; Gernay, Thomas ULiege

Poster (2017, May 02)

SAFIR is a computer program developed at University of Liege to model the behavior of building structures subjected to fire.

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See detailAnalysis of a concrete building exposed to natural fire
Sauca, Ana ULiege; Gernay, Thomas ULiege; Robert, Fabienne et al

in Wald, F.; Burgess, I.; Jelcic Rukavina, M. (Eds.) et al Proceedings of the Int. Conf. ASFE in Dubrovnik, 15-16 October 2015 (2017)

In this paper is presented the analysis of a concrete building exposed to OZone fire. The temperature development in the elements and the structural behaviour were calculated in SAFIR using beam elements ... [more ▼]

In this paper is presented the analysis of a concrete building exposed to OZone fire. The temperature development in the elements and the structural behaviour were calculated in SAFIR using beam elements for the columns and beams and shell elements for the floor slabs. The first floor was modelled and the effects of action from the upper storeys are applied as external loads. It is shown how the numerical analysis allows understanding the behaviour of the structure when exposed to a natural fire until complete cooling by analysing the evolution of displacements, the distributions of bending moments in the beams, the membrane forces in the slab, and the stresses in the elements. All this detailed information would not be available from an experimental test. [less ▲]

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