References of "Franssen, Jean-Marc"
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See detailPropagation tests with uniformly distributed cellulosic fire load
Gamba, Antonio ULiege; Charlier, Marion; Franssen, Jean-Marc ULiege

in Fire Safety Journal (2020), 117

In the recent past, the necessity to have a better understanding of fire dynamics and of the full structural response under real fires was the motivation for several large-scale non-standard fire tests ... [more ▼]

In the recent past, the necessity to have a better understanding of fire dynamics and of the full structural response under real fires was the motivation for several large-scale non-standard fire tests. Nowadays, the novel need to better comprehend the fire dynamics behind the so called “travelling fires” underlined the limitations of those non-standard fire tests. The lack of standardised procedures does not allow making effective comparisons and drawing scientific conclusion from these tests. The fire group of Liege University performed eleven non-standard or “natural fire” tests within the context of the RFCS research project TRAFIR sponsored by the E.U. Commission (grant N°754,198). The aim of this experimental campaign was to determine a uniformly distributed fuel arrangement that would lead to a medium fire growth as recommended for office buildings in Eurocode 1. This paper presents the test results in terms of fire growth rate, flame length, temperature along the flame centreline, fluxes at a distance from the fire and temperatures on wood sticks. The outcomes define a uniformly distributed fuel load arrangement leading to a desired fire development and also provide valuable experimental information on the fire dynamics related to fire spread. In conclusion, a well-established methodology to perform natural fire tests has been defined, from the ignition system up to the exact fuel arrangement. This methodology could be used in the future for natural fire tests in order to allow a comparison of different conditions (ventilations, geometry, nature of the boundaries, etc.) while considering the same fire load distribution to understand, for example, the conditions in which a travelling fire can develop or not. The experimental results reported here can also be used to validate or calibrate various existing or future sub-models developed by other authors. [less ▲]

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See detailStability in Hybrid Fire Testing using PI control
Mergny, Elke ULiege; Drion, Guillaume ULiege; Franssen, Jean-Marc ULiege

in Experimental Techniques (2020)

Widely used in earthquake engineering, Hybrid testing is promoted in various domains such as wind engineering, coastal structures and fluid-structure interaction. It also begins to be applied to fire ... [more ▼]

Widely used in earthquake engineering, Hybrid testing is promoted in various domains such as wind engineering, coastal structures and fluid-structure interaction. It also begins to be applied to fire engineering (Hybrid Fire Testing or HFT) for coupling fire tests and numerical simulations. However, HFT is still in its infancy. Yet, some tests have been performed and some algorithms have been developed. Recently, Mergny et al. [1] proposed a framework based on linear control system theory for a displacement control procedure. It uses proportional integral (PI) controller and allows performing HFT with non-linear substructures. The method was validated numerically but no analysis was provided about stability. This paper aims to describe the effects on stability of the main sources of errors in the case of HFT using PI control, namely delays, experimental errors and estimation of the stiffness of the physical substructure that is essential for most of the methodologies that have been developed so far. The research shows first through the equations of a single degree of freedom (SDOF) system that the estimation of the stiffness is a potential source of instability and affects directly the design of the PI controller. A simplified model for MDOF system was developed. Then, the research highlights that the effect of the experimental errors can involve a modification of the apparent mechanical response of the specimen and causes instability. However, this effect can be greatly limited. Finally, the delay is not a source of instability. A virtual hybrid test is performed in a steel frame and shows that the simplified model is a satisfying approximation and that described effects of the estimation of the stiffness established for a SDOF system can be observed for a complex system. [less ▲]

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See detailThe introduction and the influence of semi-rigid connections in framed structures subjected to fire
Gernay, Thomas ULiege; Franssen, Jean-Marc ULiege

in Fire Safety Journal (2020), 114

This paper describes a recent development in a finite element software dedicated to the modeling of structures in fire which deals with the way connections are simulated in global structure analyses. This ... [more ▼]

This paper describes a recent development in a finite element software dedicated to the modeling of structures in fire which deals with the way connections are simulated in global structure analyses. This development allows modeling semi-rigid, temperature-dependent connections between beam-type finite elements. It relies on the definition of additional internal degrees of freedom in the elements. The objective is to enable efficient analysis of the influence of semi-rigid connections on the global structural response and on the demands for these connections. The theory and implementation are described in a geometrically non-linear software with large displacements. Then, a 3D frame structure is analyzed as a case study. The analyses show that structural capacity and failure mode depend on the degree of rotational restraint at the beam-column connections and at the base of the columns. The maximum fire resistance is obtained for an intermediate degree of restraint between beams and columns, while higher restraints lead to an unfavorable sway failure mode. The case study illustrates the capabilities introduced by the new development, and demonstrates that the effects of the connections on global response is complex, justifying the need for practical numerical methods for design and parametric analyses of structures in fire. © 2020 Elsevier Ltd [less ▲]

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See detailToward a standardized uniformly distributed cellulosic fire load
Franssen, Jean-Marc ULiege; Gamba, Antonio ULiege; Charlier, Marion

Conference (2019, June 05)

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See detailToward a standardized uniformly distributed cellulosic fire load
Franssen, Jean-Marc ULiege; Gamba, Antonio ULiege; Charlier, Marion

in Toward a standardized uniformly distributed cellulosic fire load (2019, June 05)

This paper describes a series of experimental tests performed on uniformly distributed fire load made of wood sticks. The aim of this campaign was to define a fuel load arrangement that would lead to a ... [more ▼]

This paper describes a series of experimental tests performed on uniformly distributed fire load made of wood sticks. The aim of this campaign was to define a fuel load arrangement that would lead to a fire with the characteristics recommended for office building occupations in EN 1991-1-2. This means a fire load density of 511 MJ/m² and a medium fire propagation. The ignition procedure that was developed is described as well as the fuel arrangement that leads to a continuous isotropic fire propagation. For the 11 tests performed, the evolution of the radius of the fire is given as a function of time as well as the constant tα that characterises the t² fire. The size of the sticks is not the dominant parameter that influences the fire spread, whereas the presence or not of a ceiling has an overwhelming influence and the volumetric ratio of wood in the fire load allows controlling the fire spread. Values of the volumetric ratio are proposed that should lead to a slow, a medium or a fast fire. [less ▲]

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See detailPI Control in Hybrid Fire Testing
Mergny, Elke ULiege; Drion, Guillaume ULiege; Franssen, Jean-Marc ULiege

Conference (2019, March 13)

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See detailAn equivalent stress method to account for local buckling in beam finite elements subjected to fire
Maraveas, Chrysanthos; Gernay, Thomas ULiege; Franssen, Jean-Marc ULiege

in Journal of Structural Fire Engineering (2019), 10(3), 340-353

Purpose: The purpose of this paper is to present an improved temperature-dependent constitutive model for steel that accounts for local instabilities of slender plates using an effective stress-based ... [more ▼]

Purpose: The purpose of this paper is to present an improved temperature-dependent constitutive model for steel that accounts for local instabilities of slender plates using an effective stress-based method. This model can be easily implemented for use with Bernoulli beam finite elements (FEs) in the fire situation. Design/methodology/approach: The constitutive model is derived by calibration on parametric numerical analysis on isolated plates subject to buckling at different elevated temperatures. The model is implemented in the FE software SAFIR and validation is performed against experimental and shell element analysis results. Findings: A constitutive model based on an equivalent stress method is proposed as an efficient way to consider local buckling in steel members exposed to fire. The proposed stress–strain–temperature relationship is asymmetric and is modified in compression only, by reducing the proportional limit, the yield stress and the strain at yield stress. The reduction of these parameters depends on the plate’s boundary conditions, slenderness and temperature. The validation of the proposed model shows good agreement over a range of profile dimensions, temperatures and steel grades. Research limitations/implications: The model is still giving conservative results for large compressive load eccentricities. An enhanced model is under development to improve the predictive capability under large eccentricities. Practical implications: The proposed model, easily implemented into any finite element software, allows using fibre type (Bernoulli) beam FEs for modelling structures made of slender sections. This has major practical implications as beam elements are the workhorse used for simulating the behaviour of structures in fire. This model, thus makes it possible to simulate large structures with slender steel sections at a limited computational cost. Originality/value: The paper presents a novel steel constitutive model based on an innovative approach to capture local buckling at the material level using an equivalent stress approach. The theoretical development, validation and perspectives for future improvements are presented. © 2019, Emerald Publishing Limited. [less ▲]

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See detailHybrid fire testing in a non-linear environment using a proportional integral controller
Mergny, Elke ULiege; Gernay, Thomas ULiege; Drion, Guillaume ULiege et al

in Journal of Structural Fire Engineering (2019), 10(2), 245-258

Purpose: The purpose of this paper is to propose a new framework based on linear control system theory and the use of proportional (P) controller and proportional integral (PI) controller to address ... [more ▼]

Purpose: The purpose of this paper is to propose a new framework based on linear control system theory and the use of proportional (P) controller and proportional integral (PI) controller to address identified stability issues and control the time properties in hybrid fire testing. Design/methodology/approach: The paper approaches hybrid fire testing as a control problem. It establishes the state equation to give the general stability conditions. Then, it shows how P and PI controllers can be incorporated in the system to maintain stability. A virtual hybrid fire testing is performed on a 2D steel frame for validation and to compare the performance of the controllers. Findings: Control system theory provides an efficient framework for hybrid fire testing and rigorously formulate the stability conditions of the system. The use of a P-controller stabilises the process, but this controller is not suitable for continuous change of stiffness of the substructures. In contrast, a PI-controller handle the stiffness changes. The results of a virtual hybrid fire testing of a 2D steel frame shows that the PI-controller succeeds in reproducing the global behaviour of the frame, even if the surrounding structure is non-linear and subjected to fire. Originality/value: The paper provides a rigorous formulation of the general problem of hybrid fire testing and shows the interest of a PI controller to control the process under varying stiffness. This methodology is a step forward for hybrid fire testing because it allows capturing the global behaviour of a structure, including where the numerical substructure behaves nonlinearly and is subjected to fire. © 2019, Emerald Publishing Limited. [less ▲]

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See detailTRAFIR (TRAvelling FIRes) - Analysis of the physical parameters influencing the development of a travelling fire
Franssen, Jean-Marc ULiege; Wellens, Eric ULiege; Dumont, Fabien ULiege et al

Textual, factual or bibliographical database (2019)

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

in Franssen, Jean-Marc; Vassart, Olivier; Nadjai, Ali (Eds.) et al SiF 2018: 10th international conference on structures in fire (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 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 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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