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

in Journal of Structural Fire Engineering (in press)

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 detailPerformance-based fire design and the U.S. prescriptive guidelines: A comparative study
Elhami Khorasani, Negar; Fang, Chenyang; Gernay, Thomas ULg

in Proceedings of the 39th IABSE Symposium (2017, September 21)

Current codes and standards for fire design of structures in the United States are mainly based on design at the component level using prescriptive approaches, while performance-based design for fire can ... [more ▼]

Current codes and standards for fire design of structures in the United States are mainly based on design at the component level using prescriptive approaches, while performance-based design for fire can be used to address the needs for designing modern buildings with cost-effective solutions. Previous research shows that, when system-level performance is considered, fire protection on secondary beam elements in composite steel-concrete floor systems is not necessary due to the development of a membrane action in the concrete slab during fire. This study compares the fire design of a 9-story office building using prescriptive and performance-based designs. The safety levels of the two designs are investigated and compared. It is shown that performance-based design can be used to achieve the required level of safety currently enforced in the U.S. prescriptive guidelines, while providing an opportunity for cost reduction in fire protection material. [less ▲]

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

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 ULg; Mergny, Elke ULg; Gernay, Thomas ULg et al

in Proceedings of ASFE'17 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 detailComparative fire analysis of steel-concrete composite buildings designed following performance-based and U.S. prescriptive approaches
Elhami Khorasani, Negar; Fang, C.; Gernay, Thomas ULg

in Proceedings of the ASFE '17 Conference (2017, September 08)

Performance-based structural fire design provides a rational methodology for designing modern buildings with cost-effective solutions. However, in the United States, fire design still largely relies on ... [more ▼]

Performance-based structural fire design provides a rational methodology for designing modern buildings with cost-effective solutions. However, in the United States, fire design still largely relies on design at the component level using prescriptive approaches. With performance-based approaches, there is an opportunity to benefit from increased flexibility and reduced cost in the design, but these advantages need to be explicitly described and disseminated to promote this shift in paradigm. In this paper, a comparative analysis is conducted on multi-story steel-concrete buildings designed following performance-based and U.S. prescriptive approaches. The steel-concrete composite structure allows taking advantage of tensile membrane action in the slab during fire, and therefore removing the fire protection on secondary beam elements. The nonlinear finite element software SAFIR is used to model the behavior of the buildings under the standard ASTM fire and a natural fire determined using the two-zone fire model CFAST. The numerical simulations show that performance-based design can be used to achieve the required level of safety currently enforced in the U.S. prescriptive guidelines, while providing an opportunity for cost reduction in fire protection material. [less ▲]

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

in Proceedings of ASFE'17 Conference (2017, September 07)

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

in Proceedings of ASFE'17 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 detailFire resistance of concrete slabs acting in compressive membrane action
Molkens, Tom; Gernay, Thomas ULg; Caspeele, Robby

in Nigro, Emidio; Bilotta, Antonio (Eds.) Proceedings of the 2nd International Fire Safety Symposium - IFireSS 2017 (2017, June 08)

In building renovation, the real behaviour of reinforced concrete slabs cannot always be explained by the bending theory according to classical structural mechanics. Indeed, the bearing capacity, as ... [more ▼]

In building renovation, the real behaviour of reinforced concrete slabs cannot always be explained by the bending theory according to classical structural mechanics. Indeed, the bearing capacity, as assessed for instance by a loading test, sometimes appears to be much higher than what would be expected. This phenomenon may be caused by the activation of an arch-effect or so-called compressive membrane action (CMA) which can develop even with small vertical deformations. For a slab which is completely restrained, the presence of reinforcement becomes of lesser importance when this phenomenon is activated (except for end fields). Hence, for fire resistance purposes, it can be discussed whether reinforcement and concrete cover has a smaller influence on the bearing capacity for slabs subjected to fire which exhibit a significant concrete compressive membrane behaviour. This paper presents a loading test performed on a real concrete building which highlighted the development of CMA as the load bearing mode. It then proposes a strategy to evaluate the behaviour resulting from the development of CMA in reinforced concrete slabs at ambient and at elevated temperature based on numerical modelling. The numerical analyses are performed with the finite element software SAFIR® using a strip of layered shell elements. A plastic-damage constitutive model with an explicit transient creep formulation is used to capture the concrete behaviour at elevated temperature. [less ▲]

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See detailFire risk assessment of multi-story buildings based on fragility analysis
Gernay, Thomas ULg; Elhami Khorasani, Negar; Garlock, Maria

in Nigro, Emidio; Bilotta, Antonio (Eds.) Proceedings of the 2nd International Fire Safety Symposium - IFireSS 2017 (2017, June 07)

Recent efforts aim at assessing the fire performance of structures in a probabilistic framework. But there is still no well-established method to quantify the reliability of entire buildings. Previous ... [more ▼]

Recent efforts aim at assessing the fire performance of structures in a probabilistic framework. But there is still no well-established method to quantify the reliability of entire buildings. Previous works focused on isolated structural members, therefore not allowing for a determination of the global safety level of buildings. Here, a new methodology is developed to quantify the reliability of buildings in fire. The methodology uses Monte Carlo simulations for constructing fragility functions associated with different fire breakout locations in a building, then combines the functions to characterize the overall building conditional probability of failure, and finally incorporates the probabilistic models for intensity measure and fire occurrence likelihood. The methodology is applied to multi-story steel buildings. This work addresses fire reliability at the building scale, and therefore is useful for standardizing safety level as well as for evaluating community resilience. [less ▲]

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See detailA comparison of prescriptive and performance-based designs for fire as a primary or secondary event
Elhami Khorasani, Negar; Haase, Bryce; Fang, Chenyang et al

Scientific conference (2017, June 06)

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See detailPerformance-based Fire Safety Engineering: Challenges and Opportunities
Gernay, Thomas ULg

Conference given outside the academic context (2017)

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See detailQuantification of model uncertainties
Achenbach, Marcus; Gernay, Thomas ULg; Morgenthal, Guido

Scientific conference (2017, May 23)

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

Poster (2017, May 02)

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

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 detailEffects of various design parameters on system-level fire fragility functions for steel buildings
Elhami Khorasani, Negar; Gernay, Thomas ULg; Garlock, Maria

Conference (2017, April 07)

The existing literature in fire engineering is mostly based on single component study of structures, as opposed to system level building performance. In current practice, fire does not need to be ... [more ▼]

The existing literature in fire engineering is mostly based on single component study of structures, as opposed to system level building performance. In current practice, fire does not need to be considered as part of the structural design of the building. The required fire protection for steel components in a building is based on prescriptive design guidelines, which are based on standard fire tests on individual structural members. In addition, the fire-structure engineering has primary focused on deterministic analysis, while the field is moving towards performance-based design in recent years. Meanwhile, the scenarios leading to a fire event and the performance of the structure at elevated temperatures involve a great level of uncertainty. This work focuses on fire-structure interaction with the objective of developing fire fragility functions that capture fire damage uncertainty for the entire building (i.e., at the system-level). A fragility function provides the probability of exceeding a damage state for a given intensity measure of a given hazard. Fire fragility functions can be developed to measure the expected losses based on performance of a building structural system, rather than a single component. Different functions can be developed for buildings with different typologies (e.g. high-rise steel building with moment resisting frame, low rise steel building with bracing). This presentation derives fragility functions based on stochastic analyses of prototype buildings. In developing the fragility functions, uncertainties in the fire model, the heat transfer model and the thermo-mechanical response should be considered; but such a large number of random variables adds to the complexity of analysis and the computational time. Based on a sensitivity analysis for steel gravity frames, this work identifies the most important input parameters to be considered as random variables when developing fire fragility functions for an entire building. The sensitivity analysis for a multi-story steel building prototype is completed considering uncertainties at the compartment and building levels. At the compartment level, uncertainty in the fire scenario, compartment geometry, applied load, thermal and mechanical properties of steel and insulating materials are considered. At the building level, the influence of fire-resistance rating, building height, and occupancy type are studied. The results of this study identify the local and global parameters needed as part of deriving system-level fire fragility functions for a steel building. [less ▲]

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See detailPost-blast fire resistance of low-rise buildings through membrane action of composite floor slabs
Haase, Bryce; Elhami Khorasani, Negar; Gernay, Thomas ULg

Conference (2017, April 06)

Sever fires in buildings can lead to local failures, instability, partial or total collapse of the structure. In majority of the times, fire is a secondary event, after blast or impact, while the building ... [more ▼]

Sever fires in buildings can lead to local failures, instability, partial or total collapse of the structure. In majority of the times, fire is a secondary event, after blast or impact, while the building has experienced some damage. Examples of widely known events include the 1968 Ronan Point collapse in the UK, the 1995 Oklahoma City bombing, the World Trade Center Collapse in New York in 2001, the 2014 collapse of a building at New York’s Harlem neighborhood due to a gas explosion, and the recent 2015 collapse of a building at New York’s East Village also due to a gas explosion. The initial shock to the building can be conservatively modeled by removing an intermediate vertical supporting element (i.e. loss of load-carrying capacity in a critical element), leading to an increased span for composite floor slabs. In a lowrise building, if there is enough reinforcement throughout the slab and enough continuity and restraint, despite large deflections that will develop, the slab is capable of carrying the loads by membrane action. Fundamentally, the floor system behaves as an inverted dome structure with radial tensile forces and a compressive hoop stresses. This holds true at ambient temperature, yet a similar resisting mechanism forms during fire. Previous research and experimental work shows that fire performance of composite floor slabs can be used to reduce the fire protection requirement of the steel elements, i.e. the designer should take advantage of reserve capacity in the composite floor slab membrane action. The utilization of membrane action in the design of composite floor slabs has been used, to some extent, for mitigating collapse from single events (blast or fire only). Given that, often the initial blast is followed by a secondary fire event, this work investigates the system-level performance of low-rise damaged buildings subject to post-blast fires. The hypothesis is that, when incorporated in the design, low-rise buildings can withstand the post-blast fires through membrane action of composite floor slabs. Application of this concept, within a performance-based framework, can be used to avoid progressive collapse, or at the minimum increase fire resistance to allow for safe evacuation. This work investigates the design requirements for beam sizes, fire protection, concrete reinforcement and cover thickness to develop membrane action for a pre-defined fire resistance rating under cascading post-blast fires. [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 ULg; Franssen, Jean-Marc ULg; Gernay, Thomas ULg

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, a comparison of the reference results for the cases presented in the Annex CC with the results obtained with 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. The parametric analysis shows that the solution of SAFIR satisfies the requirement of the standard. The solution converges to the theoretical solution when the density of the mesh is increased and the value of the time step is reduced. When refining the mesh, rectangular elements converge slightly faster than triangular element; regular structured meshes are most efficient, with slight differences being observed in distorted structured meshes; unstructured meshes are somehow less efficient while being still in the acceptable range of the standard. [less ▲]

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See detailComputational models and probabilistic methods to improve infrastructure resilience to fire
Gernay, Thomas ULg

Scientific conference (2017, February 13)

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See detailPost-fire assessment of concrete structures. Safe for continued use?
Molkens, Tom; Gernay, Thomas ULg; Van Coile, Ruben

Conference (2016, November 24)

After a fire in a building, questions arise regarding the post-fire fire capacity of the structure. Assessment of post-fire capacity of structural elements should consider the residual safety level which ... [more ▼]

After a fire in a building, questions arise regarding the post-fire fire capacity of the structure. Assessment of post-fire capacity of structural elements should consider the residual safety level which, in the absence of codification, requires performing a full probabilistic analysis. Therefore, an easy-to-use method is presented which allows to make a probabilistic calculation, using only analytical formulas and a pre-calculated graph. The method is applied to a real case study, consisting of a fire that took place in an apartment building in Belgium, indicating sufficient load bearing capacity for further use. [less ▲]

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See detailUncertainties in determination of fire resistance by experimental testing and by calculation
Dumont, Fabien ULg; Gernay, Thomas ULg; Franssen, Jean-Marc ULg

Conference (2016, November 24)

In Europe, certification of the fire resistance of building construction elements can be assessed by experimental testing or by calculation. To date, both communities (testing and calculation) express the ... [more ▼]

In Europe, certification of the fire resistance of building construction elements can be assessed by experimental testing or by calculation. To date, both communities (testing and calculation) express the fire resistance results in a deterministic way, i.e. each fire resistance result consists in a single number as if there was no uncertainty. However, when asking different partners within a community to assess the fire resistance of a given element of building construction subjected to a given fire scenario (a so-called “round robin” exercise), the reported results exhibit a very significant variability. Recent efforts have been undertaken to evaluate the extent of the scatter for fire resistance results, i.e. a process of "uncertainty evaluation". This process recognizes the fact that, for a given element of building construction and a given fire scenario, only a probability distribution (as opposite to a deterministic value) can be attributed to the fire resistance result. This approach opens the door to probabilistic reporting as an alternative to deterministic one. [less ▲]

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