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

in 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 Proceedings of the 2nd International Fire Safety Symposium - IFireSS 2017 (2017, June 08)

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 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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See detailA method for measuring the sensitivity of building structural members to fire decay phases
Gernay, Thomas ULg

in Acta Polytechnica (2016), 56(4), 344-352

Fire brigades face a major threat when intervening in a building in fire: the possibility of structural collapse during the cooling phase of the fire, or soon thereafter. Currently this threat is ... [more ▼]

Fire brigades face a major threat when intervening in a building in fire: the possibility of structural collapse during the cooling phase of the fire, or soon thereafter. Currently this threat is amplified by the fact that the behaviour of structures after the time of peak gas temperature is not well understood, and is not taken into account in the design. This work presents an analysis of the behaviour of different structural members under natural fires and develops a method to characterize their sensitivity to fire decay phases. Thermo-mechanical numerical simulations based on the non-linear finite element method are conducted using the parametric fire model of Eurocode to represent natural fires. Results show that, for all the studied members (column, beam) and materials (reinforced concrete, steel and timber), structural failure during or after the cooling phase of a fire is a possible event. The major factors that promote delayed structural failure are the thermal inertia and the constituting material of the member. A method, based on a new indicator, is proposed to quantify the propensity to delayed failure for structural members under natural fire. This work enhances the understanding of the structural behaviour under natural fires and has important implications for the safety of the fire brigades and people proceeding to a building inspection after a fire. [less ▲]

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See detailLoadbearing capacity criteria in fire resistance testing
Dumont, Fabien ULg; Wellens, Eric ULg; Gernay, Thomas ULg et al

in Materials and Structures (2016), 49(11), 4565-4581

The European system for fire testing and classification of loadbearing building elements lacks consistency because the two standards that have to be applied prescribe different criteria for assessing the ... [more ▼]

The European system for fire testing and classification of loadbearing building elements lacks consistency because the two standards that have to be applied prescribe different criteria for assessing the loadbearing performance. This article analyzes the implications of the present conflict between the standard for testing and the standard for classification. The prescribed criteria for loadbearing performance are related to the exceedance of deflection and rate of deflection thresholds. A database of 46 fire resistance tests performed at the University of Liege is collected that contains the time at which these thresholds are reached in fire tests with different typologies of elements (walls, floors, columns and beams). Then, the loadbearing performance (and hence the fire resistance rating) can be derived according to the two standards. The evolutions of deflection and rate of deflection during the tests are also analyzed to gain a better understanding of the adequacy of the standards. The selection of one or the other standard affects the time at which “failure” is deemed to occur in fire tests. Statistically speaking, the difference in terms of failure time that results from using one or the other standard has a 25% probability to exceed 10%. In certain cases, this results in a difference in fire resistance rating; this was observed for 3 of the analyzed tests. The apparent contradiction in two codes in application has potential practical implications and therefore needs to be solved. The article suggests some guidelines for defining homogenized and consistent criteria. [less ▲]

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See detailNew features in SAFIR® 2016 - SWS 2016
Franssen, Jean-Marc ULg; Gernay, Thomas ULg

Scientific conference (2016, October 27)

Presentation of the new capabilities and developments in the version 2016 of SAFIR, a non linear software dedicated to the analysis of the behaviour of structures in fire.

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See detailDeveloping system-level fragility functions for performance-based fire engineering of buildings
Gernay, Thomas ULg; Elhami Khorasani, Negar

Scientific conference (2016, October 20)

This research contributes to the current efforts for developing probabilistic methods in structural fire engineering (SFE) to foster the shift towards performance-based design in the field. A methodology ... [more ▼]

This research contributes to the current efforts for developing probabilistic methods in structural fire engineering (SFE) to foster the shift towards performance-based design in the field. A methodology is presented to assess the risk related to structural failure due to fire in multi-story buildings. At the core of this methodology is the concept of fragility functions, which allows quantifying in a systematic way the effects of the uncertainties in both demand and capacity parameters on the reliability level. The fragility functions, adopted here for the purpose of SFE, yield the conditional probability to reach predefined damage states as a function of an intensity measure of the fire. The damage states are grouped in categories such as ‘slight’, ‘moderate’, ‘extensive’, and ‘complete’, for estimating the magnitude of the damage. The fragility functions are defined for an entire building and depend on parameters such as the structural type and the fire resistance rating of the structural components. As the functions give conditional probabilities, they are completed with probabilistic models for the occurrence of a fire in the building (i.e. likelihood of the hazard) and the expected value of the fire load density (i.e. intensity of the hazard). These models depend on the building occupancy type, surface area, and active fire protection measures. Finally, one can obtain the (total) probability to reach different levels of potential damage for buildings of different typologies, structural design, size and occupancy. In addition, similar to earthquake engineering, one can also estimate the probability of reaching a certain damage state for a given probability of fire hazard. The methodology is illustrated for prototype multi-story steel buildings. An important contribution is the quantification of the safety level at the building scale, as opposed to an individual component. The results provide an insight for the discussion about the evolution of the design codes for a better standardization of this safety level. [less ▲]

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See detailProbabilistic Measures of Earthquake Effects on Fire Performance of Tall Buildings
Elhami Khorasani, Negar; Gernay, Thomas ULg; Garlock, Maria

in Zingoni (Ed.) Proceedings of the Sixth International Conference on Structural Engineering, Mechanics and Computation (2016, September 06)

Cascading multi-hazard events, such as fires following an earthquake, can trigger progressive collapse of structures. Risk or the probability of reaching a limit state after an extreme event is related to ... [more ▼]

Cascading multi-hazard events, such as fires following an earthquake, can trigger progressive collapse of structures. Risk or the probability of reaching a limit state after an extreme event is related to (a) the probability of occurrence of the hazard, and (b) the probability of reaching the limit state given the hazard. In this paper, earthquake effects on fire performance of tall buildings in a community are studied. First, the proba-bility of fire ignition due to an earthquake is modeled based on historical data and properties of the built en-vironment. In the second step, the effect of earthquake on structural fire performance of a steel frame is studied using system level probabilistic approaches. The results show that the earthquake does not increase the probability of reaching different limit states under fire, however, post earthquake fire can increase the drift demand on columns located on the perimeter of the structure, and may cause instability. [less ▲]

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See detailFire Performance of Columns made of Normal and High Strength Concrete: A Comparative Analysis
Gernay, Thomas ULg

in Key Engineering Materials (2016), 711

The use of high strength concrete (HSC) in multi-story buildings has become increasingly popular. Selection of HSC over normal strength concrete (NSC) allows for reducing the dimensions of the columns ... [more ▼]

The use of high strength concrete (HSC) in multi-story buildings has become increasingly popular. Selection of HSC over normal strength concrete (NSC) allows for reducing the dimensions of the columns sections. However, this reduction has consequences on the structural performance in case of fire, as smaller cross sections lead to faster temperature increase in the section core. Besides, HSC experiences higher rates of strength loss with temperature and a higher susceptibility to spalling than NSC. The fire performance of a column can thus be affected by selecting HSC over NSC. This research performs a comparison of the fire performance of HSC and NSC columns, based on numerical simulations by finite element method. The thermal and structural analyses of the columns are conducted with the software SAFIR®. The variation of concrete strength with temperature for the different concrete classes is adopted from Eurocode. Different configurations are compared, including columns with the same load bearing capacity and columns with the same cross section. The relative loss of load bearing capacity during the fire is found to be more pronounced for HSC columns than for NSC columns. The impact on fire resistance rating is discussed. These results suggest that consideration of fire loading limits the opportunities for use of HSC, especially when the objective is to reduce the dimensions of the columns sections. [less ▲]

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See detailA Novel Methodology for Hybrid Fire Testing
Sauca, Ana ULg; Gernay, Thomas ULg; Robert, Fabienne et al

in Proceedings of the 6th European Conference on Structural Control (2016, July 11)

This paper describes a novel methodology for conducting stable hybrid fire testing (HTF). During hybrid fire testing, only a part of the structure is tested in a furnace while the reminded structure is ... [more ▼]

This paper describes a novel methodology for conducting stable hybrid fire testing (HTF). During hybrid fire testing, only a part of the structure is tested in a furnace while the reminded structure is calculated separately, here by means of a predetermined matrix. Equilibrium and compatibility at the interface between the tested “physical substructure” and the “numerical substructure” is maintained throughout the test using a dedicated algorithm. The procedures developed so far are sensitive to the stiffness ratio between the physical and the numerical substructure and therefore they can be applied only in some cases. In fire field, the stiffness of the heated physical substructure may change dramatically and the resulting change in stiffness ratio can lead to instability during the test. To overcome this drawback, a methodology independent of the stiffness ratio has been developed, inspired from the Finite Element Tearing and Interconnecting (FETI) method, which has been originally developed for substructuring in numerical analyses. The novel methodology has been successfully applied to a hybrid fire test in a purely numerical environment, i.e. the physical substructure was also modelled numerically. It is shown that stability does not depend on the stiffness ratio and that equilibrium and compatibility can be consistently maintained at the interface during the fire. Finally, the ongoing experimental program aimed at employing and experimentally validating this methodology is described. [less ▲]

Detailed reference viewed: 87 (34 ULg)