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See detailNew features in SAFIR: Damage-Plastic Multiaxial Model for Concrete
Gernay, Thomas ULg; Franssen, Jean-Marc ULg

Scientific conference (2011, November 15)

The need for robust, reliable multiaxial constitutive relationships for concrete is a challenging issue in structural fire engineering. A new damage-plastic model has been developed to capture the ... [more ▼]

The need for robust, reliable multiaxial constitutive relationships for concrete is a challenging issue in structural fire engineering. A new damage-plastic model has been developed to capture the development of permanent strains and the degradation of elastic properties in concrete subjected to thermo-mechanical loading. This model has been implemented in the software SAFIR for using with SOLID finite elements (multiaxial model) and with SHELL finite elements (plane stress model). [less ▲]

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See detailNew features in SAFIR: Transient Creep in Eurocode Concrete Model
Gernay, Thomas ULg; Franssen, Jean-Marc ULg

Scientific conference (2011, November 15)

A new formulation of the Eurocode 2 concrete model at elevated temperature has been implemented in which the transient creep strain is treated by an explicit term in the strain decomposition. This new ... [more ▼]

A new formulation of the Eurocode 2 concrete model at elevated temperature has been implemented in which the transient creep strain is treated by an explicit term in the strain decomposition. This new model gives the same answer as the Eurocode model when the load and the temperature increase, but the new model is better than the Eurocode model at capturing the concrete behavior when the load or the temperature decrease owing to the explicit transient creep term. This new concrete model, called Explicit Transient Creep Eurocode model (ETC), has been implemented in the software SAFIR. [less ▲]

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See detailStructural Behavior of Concrete Columns under Natural Fires including Cooling Down Phase
Gernay, Thomas ULg; Dimia, M. S.

in Barros, Helena; Faria, Rui; Pina, Carlos (Eds.) et al Proceedings of The International Conference on Recent Advances in Nonlinear Models - Structural Concrete Applications (2011, November)

This study deals with the structural behavior of concrete columns subjected to natural fire, with special focus on the cooling down phase. As the reliability of the numerical simulations largely depends ... [more ▼]

This study deals with the structural behavior of concrete columns subjected to natural fire, with special focus on the cooling down phase. As the reliability of the numerical simulations largely depends on the validity of the constitutive models that are used, this issue is addressed in details in the first part of the paper. It is found that the current concrete model of Eurocode may not be adapted for representing the behavior of concrete during a cooling phase because the effects of transient creep are incorporated implicitly in the mechanical strain term. A formulation of the Eurocode concrete model that contains an explicit term for transient creep strain has been developed and, after implementation in the software SAFIR, it was used for the numerical simulations presented in this paper. In its second part, the study gives an insight into the possibility of collapse of reinforced concrete columns during and after the cooling phase of the natural fire. It is found that failure during the cooling phase of a fire is a possible event and, more dangerous, that a failure of the concrete columns is still possible when the fire has been completely extinguished. The main mechanisms that lead to this type of failure are found to be the delayed increase of temperature in the central zones of the element and the additional loss of concrete strength during the cooling phase of the fire. A parametric study shows that the most critical situations with respect to delayed failure arise for short fires and for columns with low slenderness or massive sections. The numerical analyses have been performed also with the concrete model of Eurocode and the results also show a risk of delayed collapse. Yet, the occurrence of collapse during or after the cooling phase is predicted more often with the explicit creep model than with the implicit model of Eurocode, which suggests that the way the transient creep effects are handled in the Eurocode model may lead to unsafe results when considering the cooling phase of a fire. [less ▲]

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See detailCollapse of concrete columns during and after the cooling phase of a fire
Dimia, Mohamed Salah; Guenfoud, Mohamed; Gernay, Thomas ULg et al

in Journal of Fire Protection Engineering (2011), 21(4), 245263

This paper presents a study performed on the collapse of reinforced concrete columns subjected to natural fire conditions during and after the cooling phase of the fire. The aim is, first, to highlight ... [more ▼]

This paper presents a study performed on the collapse of reinforced concrete columns subjected to natural fire conditions during and after the cooling phase of the fire. The aim is, first, to highlight the phenomenon of collapse of concrete columns during and after the cooling phase of a fire and then, to analyze the influence of some determinant parameters. The main mechanisms that lead to this type of failure are found to be the delayed increase of the temperature in the central zones of the element and the additional loss of concrete strength during the cooling phase of the fire. A parametric study is performed considering different fires and geometric properties of the column. This shows that the most critical situations with respect to delayed failure arise for short fires and for columns with low slenderness or massive sections. [less ▲]

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See detailSimplified Fire Design for Slim Floor Beams
Zaharia, Raul; Duma, Diana Maria ULg; Vassart, Olivier et al

in Dunai, Laszlo (Ed.) Proceedings of the 6th European Conference on Steel and Composite Structures (2011, September 02)

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See detailSAFIR Materials Manual - SILCON_ETC, CALCON_ETC
Gernay, Thomas ULg; Franssen, Jean-Marc ULg

Report (2011)

This document describes the material constitutive models SILCON_ETC and CALCON_ETC, which are uniaxial material models implemented in the software SAFIR (from version 2011.b.0). The material models SILCON ... [more ▼]

This document describes the material constitutive models SILCON_ETC and CALCON_ETC, which are uniaxial material models implemented in the software SAFIR (from version 2011.b.0). The material models SILCON_ETC and CALCON_ETC are based on the Explicit Transient Creep Eurocode constitutive model (ETC model) for concrete at elevated temperature, which has been developed at University of Liege by the authors of this document. [less ▲]

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See detailSimplified method for the temperature distribution in slim floor beams
Zaharia, Raul; Duma, Diana Maria ULg; Vassart, Olivier et al

in Wald, F.; Horova, K.; Jirku, J. (Eds.) Proceedings of International Conference Applications of Structural Fire Engineering (2011, April 29)

From extensive numerical thermal simulations made with SAFIR, simple design equations have been derived that allow calculating the temperature in slim floor sections subjected to an ISO 834 fire.

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See detailEconomic analysis of Stainless Steel- Reinforced Concrete members designed for a Fire Resistance of 2 hours
Gernay, Thomas ULg; Franssen, Jean-Marc ULg

Report (2011)

While Stainless steel is used primarily for its corrosion resistance, there is a growing interest in other properties, such as mechanical, high temperature resistance, aesthetics and others. The ... [more ▼]

While Stainless steel is used primarily for its corrosion resistance, there is a growing interest in other properties, such as mechanical, high temperature resistance, aesthetics and others. The properties at high temperatures (400 – 650°C ) of stainless steels are known and put to use in a number of applications such as steam turbines and equipment for the chemical industry. Some research on the fire resistance of stainless steels has been carried out for welded I beams and for concrete-filled tubes, with positive results. However, there are no published results on the behavior of concrete reinforced with stainless steel rebar. In a preliminary research program conducted by the University of Liege for ISSF, a preliminary assessment of the performance of stainless steel reinforced concrete has been carried out, using computer simulation methods. This preliminary study has shown that stainless steel reinforced concrete members can behave better than carbon steel reinforced concrete members in fire situation. However, an economic analysis is still needed to determine whether stainless steel reinforcement can be interesting for practical applications. This report is divided in two parts. The first part presents the assumptions and the results of the numerical simulations performed by University of Liege. The numerical simulations aim to design stainless and carbon steel -reinforced concrete members satisfying to a fire resistance of 2 hours (Standard fire conditions). The two structural members considered in this study are a reinforced concrete beam and a composite slab (with the so-called « membrane » behavior). The numerical simulations are performed with the SAFIR 20011.a.3 software developed in University of Liege. The second part presents the assumptions and the results of the economic analysis of the structural members designed in the first part. The stainless and carbon steel –reinforced solutions for a fire resistance of 2 hours are compared on an economic basis. [less ▲]

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See detailNonlinear numerical analysis of ship impact on lock gates
Gernay, Thomas ULg

in Van Schel, L (Ed.) PIANC Yearbook 2010 (2011)

This paper focuses on ship impact analysis on lock gate. First, the lock gate structure is determined by an elastic design and optimization process. Then, a nonlinear numerical analysis by finite elements ... [more ▼]

This paper focuses on ship impact analysis on lock gate. First, the lock gate structure is determined by an elastic design and optimization process. Then, a nonlinear numerical analysis by finite elements is conducted to study the response of the lock gate in case of ship impact. It is shown that the elastically optimized structure is not able to resist significant impacts, because of the buckling of its reinforcement elements; the gate is thus reinforced. Finally, several ship impact analyses are conducted on the reinforced gate and they highlight the influence of the stiffener dimensions and the impact zone on the structural behavior of the gate. The results of the numerical analyses underline the importance of the development of a global plastic mechanism with the purpose of dissipating a large amount of energy. [less ▲]

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See detailDevelopment of Multiaxial Constitutive Relationships for Concrete
Gernay, Thomas ULg

Scientific conference (2011, March 18)

Recent research in structural fire engineering has shown that concrete or composite building structures can develop unexpected modes of strength when subjected to fire. Under certain conditions, a ... [more ▼]

Recent research in structural fire engineering has shown that concrete or composite building structures can develop unexpected modes of strength when subjected to fire. Under certain conditions, a structure will present a robust behavior that can dramatically increase its fire resistance compared to the fire resistance calculated by a predictive approach. An example of such robust behavior is the membrane action that can be developed by a structural slab in fire. However, the numerical simulation of such behaviors requires the development of reliable and accurate multiaxial constitutive relationships for modelling the behavior of concrete. This presentation is based on the work performed by the author during a six month research stay at CEA Saclay, in the team of Alain Millard. The aim of the research stay was to develop a concrete multiaxial model that can be used for the numerical analysis by the finite elements method of concrete structures in fire. To be able to accurately simulate the structural behavior during every phases of a natural fire, the concrete model includes plasticity and damage phenomena. The main features and parameters of the model are presented and its implementation in the softwares SAFIR and CAST3M is briefly discussed. Then, a few applications are given and the presentation ends with a comment on the remaining issues and perspectives. [less ▲]

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See detailDéveloppement d'un modèle constitutif multiaxial de béton
Gernay, Thomas ULg; Millard, Alain; Franssen, Jean-Marc ULg

Scientific conference (2011, March 03)

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See detailA Comparison Between Explicit and Implicit Modelling of Transient Creep Strain in Concrete Uniaxial Constitutive Relationships
Gernay, Thomas ULg; Franssen, Jean-Marc ULg

in Proceedings of the Fire and Materials 2011 Conference (2011, February)

Transient creep strain has to be included within the constitutive relationships for concrete at high temperatures. However, the necessity of taking into account this term explicitly is not clearly defined ... [more ▼]

Transient creep strain has to be included within the constitutive relationships for concrete at high temperatures. However, the necessity of taking into account this term explicitly is not clearly defined. In the Eurocode 2 uniaxial concrete material model, transient creep is included implicitly. This paper aims to highlight the capabilities and limitations of concrete uniaxial models at elevated temperatures for thermo-mechanical behaviour modelling, depending on the implicit or explicit consideration of transient creep strain in the model. The characteristics inherent to the two types of models are described and compared. It appears that one of the major limitations of implicit models concerns the unloading stiffness because implicit models treat transient creep as reversible. Based on numerical analysis performed on loaded concrete columns subjected to natural fire, it is shown that the stress-temperature paths experienced by structural concrete are varied and complicated and that concrete material models cannot handle properly these complex situations of unsteady temperatures and stresses without explicit consideration of transient creep. The paper proposes a new formulation of the Eurocode 2 concrete material model that contains an explicit term for transient creep. The new model is implemented in the software SAFIR and validated against experimental data of the mechanical strain developed by concrete cylinders under different unsteady temperatures and loads. It is shown that the actual material behaviour is better matched with the new explicit model than with the current implicit Eurocode 2 model. Finally, a comparison is given between experimental and calculated results on an axially restrained concrete column subjected to heating and cooling. [less ▲]

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See detailAnalysis of ship impact on lock gates - Seine-Escaut Est waterway
Gernay, Thomas ULg; Rigo, Philippe ULg

in Mathematical Modelling in Civil Engineering (2010), 6(4), 43-55

This paper presents a ship impact analysis on lock gates. The case study is the downstream lock gates of the one of the four new locks planned within the framework of the “Seine-Escaut Est (SEE)” project ... [more ▼]

This paper presents a ship impact analysis on lock gates. The case study is the downstream lock gates of the one of the four new locks planned within the framework of the “Seine-Escaut Est (SEE)” project in the Walloon Region of Belgium. The design and optimization process of the gate was realized with the LBR5 lock gate optimization software considering the cost and weight aspects of the structure. This method led to an optimized solution of the lock gate on which further studies were concentrated. After a brief overview of the state of art of ship impact analysis on lock gates, it was decided to perform a quasi-static analysis by finite elements. The non linear finite elements software FINELG was used to conduct a non linear numerical analysis of the effect of a boat impact on the gate. Several analyses were performed that highlighted the influence of the stiffener dimensions and the influence of the impact zone on the gate structural behavior submitted to impact. Finally, two different behaviors have been distinguished, a ductile one and a fragile one. The results showed the importance of the development of a global plastic mechanism, thanks to a ductile behavior, with the purpose of dissipating a large amount of energy. [less ▲]

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See detailOptimization and analysis of lock gates in the framework of the "Seine-Escaut Est" waterway upgrading
Gernay, Thomas ULg

in Bulletin of the Permanent International Association of Navigation Congresses (2010), (141), 11-26

This paper presents a research study performed on lock gates. It concerns the downstream lock gate of the one of the four new locks planned within the framework of the “Seine-Escaut Est (SEE)” project in ... [more ▼]

This paper presents a research study performed on lock gates. It concerns the downstream lock gate of the one of the four new locks planned within the framework of the “Seine-Escaut Est (SEE)” project in the Walloon Region of Belgium. At the stage of the basic preliminary design, it was decided to use four identical gates, all suspended and moved transversally to the lock. On this basis, the present work tackles different aspects of the lock gate study. The aim is double: on the one hand, to advance in the study of the four SEE project downstream lock gates, and on the other hand, to focus more particularly on lock gate structural analysis, notably the design, optimization and structural behavior in the case of ship impact. First, the design and optimization of the gate are performed, using the LBR5 lock gate optimization software and a linear elastic analysis. An optimized solution is obtained considering the best compromise between the cost and weight aspects of the structure. Then, this optimized gate is modeled with the nonlinear finite elements software FINELG. This program is used to conduct non linear numerical analysis of the effect of boat impact on the previously optimized downstream gate. Several analyses are performed, which allow for a discussion on the influence of the stiffener dimensions and the impact zone on the structural behavior of the gate submitted to the impact. Two different behaviors are brought to light, a ductile one and a fragile one. The results of the numerical analysis underline the importance of the development of a global plastic mechanism with the purpose of dissipating a large amount of energy. Finally, an analytical model presented in literature allows for the simplified calculation of the gate theoretical strength in case of ship impact, and the calculated value is compared with the computed results. [less ▲]

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See detailFICEB W.P.6 final report: Numerical simulations of the large scale fire test
Gernay, Thomas ULg; Franssen, Jean-Marc ULg

Report (2010)

This report presents the results of the numerical simulations performed by University of Liege in the framework of work package 6 of the FICEB project financed by the Research Fund for Coal and Steel. A ... [more ▼]

This report presents the results of the numerical simulations performed by University of Liege in the framework of work package 6 of the FICEB project financed by the Research Fund for Coal and Steel. A full scale fire test was performed in Ulster on February 27th 2010 on a composite floor for analysing the behaviour of long cellular steel beams in a complete compartment office in building structure under realistic fire conditions. The aim was to study the possibility of tensile membrane action to develop when the unprotected steel beams in the central part of the floor are made of cellular beams. Predictive numerical simulations of the test have been performed with the software SAFIR in order to define the appropriate structure to be used for the full scale fire test. As predicted, the structure was able to withstand the test without collapse. After the test, the results of the predictive simulations have been compared to the measured results, showing relatively good agreement. [less ▲]

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See detailPreliminary Research Study on the Fire Resistance of Stainless Steel-Reinforced Concrete members
Gernay, Thomas ULg; alonso, Alain; Franssen, Jean-Marc ULg

Report (2010)

In this project, it is examined whether and under which conditions the good resistance to high temperature of stainless steel bars can lead to better fire resistance when used in reinforced concrete ... [more ▼]

In this project, it is examined whether and under which conditions the good resistance to high temperature of stainless steel bars can lead to better fire resistance when used in reinforced concrete columns, beams and slabs working in tensile membrane action. [less ▲]

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See detailConsideration of Transient Creep in the Eurocode Constitutive Model for Concrete in the Fire situation
Gernay, Thomas ULg; Franssen, Jean-Marc ULg

in Kodur, Venkatesh; Franssen, Jean-Marc (Eds.) Proceedings of the Sixth International Conference Structures in Fire (2010, June)

This paper presents a new formulation of the generic Eurocode 2 concrete model that contains an explicit term for consideration of the transient creep. The simplicity and generic characteristics of the ... [more ▼]

This paper presents a new formulation of the generic Eurocode 2 concrete model that contains an explicit term for consideration of the transient creep. The simplicity and generic characteristics of the Eurocode model are preserved and the new explicit formulation is calibrated to give the same results as the implicit formulation that is proposed in the Eurocode when the material is heated under constant load. However, the improvements allow taking into account with more accuracy the phenomenon of transient creep in concrete under more complex situations such as, for example, the cooling phase of a fire. The differences between the two formulations are highlighted for a simple structure. A comparison is given between experimental and calculated results on a centrally loaded concrete column submitted to heating-cooling sequence. [less ▲]

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See detailNumerical modelling of membrane action of composite slabs in fire situation
Vulcu, Cristian; Gernay, Thomas ULg; Zaharia, Raul et al

in Kodur, Venkatesh; Franssen, Jean-Marc (Eds.) Proceedings of the Sixth International Conference Structures in Fire (2010, June)

Membrane action in fire is now an intensively researched area, for which more improvement is always necessary. The paper presents some numerical simulations, done with the SAFIR program, in order to ... [more ▼]

Membrane action in fire is now an intensively researched area, for which more improvement is always necessary. The paper presents some numerical simulations, done with the SAFIR program, in order to derive more simple models for representing the partially protected composite floors in fire situation. The numerical models are calibrated using the results of three full scale tests that have been performed in recent years. [less ▲]

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See detailLarge-scale fire test of unprotected cellular beam acting in membrane action
Vassart, Olivier; Bailey, C. G.; Hawes, M. et al

in Franssen, Jean-Marc; Kodur, Venkatesh (Eds.) Proceedings of the Sixth International Conference Structures in Fire (2010, June)

This paper describes a full scale fire test performed recently on a composite floor for analysing the possibility of tensile membrane action to develop when the unprotected steel beams in the central part ... [more ▼]

This paper describes a full scale fire test performed recently on a composite floor for analysing the possibility of tensile membrane action to develop when the unprotected steel beams in the central part of the floor are made of cellular beams. The natural fire was created by a wood crib fire load of 700 MJ/m² and the 9 x 15 m floor survived the fire that peaked at 1000°C and lasted for 90 minutes. Blind predictions of the air temperature development by the software Ozone and of the structural behaviour by the software SAFIR which proved quite satisfactory are also described. [less ▲]

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