A multiaxial constitutive model for concrete in the fire situation

in Proceedings of the 13th Fire and Materials Conference (2013, January 28)

Performance-based design in fire engineering leads to increasing demand for advanced temperature-dependent material models for the load bearing materials used in building structures. These models must be ... [more ▼]

Performance-based design in fire engineering leads to increasing demand for advanced temperature-dependent material models for the load bearing materials used in building structures. These models must be valid in natural fire situations including cooling down phase and must be sufficiently robust for complex numerical calculations such as, for example, the analysis of tensile membrane action in composite slabs. Although structural concrete is widely used in civil engineering, proper modelling of its thermo-mechanical behaviour remains a challenging issue for engineers mainly because of the complexity of the phenomena that result from the microcracking process in this material and because of the necessity to ensure the numerical robustness of the models. This paper presents a new multiaxial concrete model based on a plastic-damage formulation and developed to meet the specific requirements of structural fire engineers and researchers. The model, which incorporates an explicit term for transient creep strain and encompasses a limited number of material parameters, has been implemented in a finite element software dedicated to the nonlinear analysis of structures in fire. The paper presents a series of numerical simulations conducted to highlight the model ability to capture the main phenomena that develop in concrete under fire (permanent strains, degradation of the elastic properties, unilateral effect) as well as its ability to be used for the fire analysis of large-scale structural elements. As an example, the new concrete model is used in the numerical analysis of a full scale fire test on a composite steel-concrete slab and it is shown that the computed and measured results agree. [less ▲]

Experimental and numerical investigation of high-strength steel circular columns subjected to fire

in Journal of Constructional Steel Research (2013), 80

This paper presents an experimental–numerical study on the behaviour of High Strength Steel (HSS) columns at elevated temperature, both on Circular Hollow Sections (CHS) and on a Concrete Filled Tube (CFT ... [more ▼]

This paper presents an experimental–numerical study on the behaviour of High Strength Steel (HSS) columns at elevated temperature, both on Circular Hollow Sections (CHS) and on a Concrete Filled Tube (CFT). The measured yield strength of the circular sections was in the order of 820 MPa. In detail, three HSS CHS and a HSS CFT were tested under the standard ISO fire with constant eccentric compression applied load. The evolution of temperature and deformation patterns were measured by means of a comprehensive instrumentation made of thermocouples and displacement transducers. Numerical analyses were performed and compared with experimental data by employing stress–strain relationships of carbon steel at elevated temperatures provided by the Eurocodes associated to two different sets of reduction factors: i) those provided by the Eurocodes valid up to S460 steel grades; and ii) those proposed in the literature and based on tests on HSS. [less ▲]

Simplified design method for slim floor beams exposed to fire

in Proceedings of NSCC2012 (2012, September 07)

One of the most important advantages of using the slim or integrated floor beams (SFB and IFB supporting full concrete slab, precast units or steel deck composite slab) is a significant fire resistance ... [more ▼]

One of the most important advantages of using the slim or integrated floor beams (SFB and IFB supporting full concrete slab, precast units or steel deck composite slab) is a significant fire resistance. However, despite of its common use in construction, no specific simplified calculation methods for the fire resistance of IFB and SFB exist in the Eurocode. This study, based on existing calculation rules of Eurocode 4, a parametrical study using soft-ware SAFIR and fire tests results, define a set of formulas to determine the thermal field and to deduce the mechanical resistance from classical plastic design. [less ▲]

A formulation of the Eurocode 2 concrete model at elevated temperature that includes an explicit term for transient creep

in Fire Safety Journal (2012), 51

The first objective of this paper is to highlight the capabilities and limitations of concrete uniaxial constitutive models at elevated temperatures for thermo-mechanical behavior modeling, depending on ... [more ▼]

The first objective of this paper is to highlight the capabilities and limitations of concrete uniaxial constitutive models at elevated temperatures for thermo-mechanical behavior modeling, 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. 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 second objective of the paper is to propose 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 behavior is better matched with the new explicit model than with the current implicit Eurocode 2 model. Finally, a comparison is given between experimental and computed results on a centrally loaded concrete column submitted to heating–cooling sequence. [less ▲]

Development of an interface between CFD and FE software

in Fontana, Mario; Frangi, Andrea; Knobloch, Markus (Eds.) Proceedings of the 7th International Conference on Structures in Fire (2012, June 06)

The paper presents the assumptions and the issues that arise when developing an integrated modelling methodology between a Computational Fluid Dynamics (CFD) software applied to compartment fires and a ... [more ▼]

The paper presents the assumptions and the issues that arise when developing an integrated modelling methodology between a Computational Fluid Dynamics (CFD) software applied to compartment fires and a Finite Element (FE) software applied to structural systems. In particular, a weak coupling approach used to simulate a fire exposed structure by modelling the fire development in the compartment, the heat penetration in the structure and the mechanical response is described. The advantages and the disadvantages of such a technique are highlighted compared to a full coupling that conversely takes into account all mutual interactions. The favourable aspect of computing the thermal response of the structure in the FE model in order to avoid modelling the structure in the CFD model is underlined, namely a sensitive reduction of computational demand. Finally, a practical application is presented. [less ▲]

Branveiligheid - Brandveiligheid en berekening van de brandwerendheid van staalconstructies voor gebouwen volgens Eurocode 3

Book published by Infosteel (2012)

Dit boek behandelt in de eerste drie hoofdstukken het onderwerp brandveiligheid en de berekening van de brandwerendheid van staalconstructies voor gebouwen volgens Eurocode 3. Hoofdstuk 1 omschrijft de ... [more ▼]

Dit boek behandelt in de eerste drie hoofdstukken het onderwerp brandveiligheid en de berekening van de brandwerendheid van staalconstructies voor gebouwen volgens Eurocode 3. Hoofdstuk 1 omschrijft de doelstellingen van brandveiligheid aan de hand van het gedrag van een brand en bespreekt de maatregelen die een ontwerper kan nemen om te voldoen aan de eisen voor brandveiligheid en de wettelijk eisen. Hoofdstuk 2 gaat over het berekenen van de brandwerendheid van een staalconstructie met betrekking tot bezwijken. Een eenvoudig berekeningsmodel volgens Eurocode 3 wordt besproken en is geschikt voor trekstaven, niet-kipgevoelige liggers, kolommen én kipgevoelige liggers. Voor de berekening van geïntegreerde liggers, zowel onbekleed als bekleed wordt een geavanceerd rekenmodel gebruikt en wordt tevens een alternatieve vereenvoudigde methode voorgesteld. Hoofdstuk 3 behandelt het onderwerp fire safety engineering; een relatief nieuw vakgebied, waarbij fysische modellen worden gebruikt om het gedrag van een brand – en het effect hiervan op bouwwerken en de gebruikers – te beschrijven. Er worden vier situaties besproken die met fire safety engineering in de praktijk al zijn te berekenen: lokale branden, compartimentsbranden (zonder én met flashover), staalconstructies die zich buiten het gebouw bevinden in de buitenlucht én het systeemgedrag van een staalconstructie. Dit laatste wordt geillustreerd aan de hand van een staalplaat-betonvloer waarbij het membraaneffect in acht wordt genomen. Hoofdstuk 4 tenslotte bevat dertien ontwerptabellen voor het eenvoudig bepalen van een aantal rekenparameters zoals de afname van de effectieve vloeigrens en de elasticiteitsmodulus, de reductiefactor op de belastingen bij brand, de profielfactoren voor I-profielen, de staaltemperatuur na een bepaalde tijd (in functie van de profielfactor) en de kritieke staaltemperatuur voor kolommen (in functie van de benuttinggraad en slankheid). [less ▲]

Heat transfer and structural response modelling of concrete filled steel hollow section columns

in Proc; ACOME (2012)

Numerical modelling is a very useful tool to predict the fire resistance of a structure, or to reproduce artificially what has happened during a real fire. SAFIR, a non linear computer code developed at ... [more ▼]

Numerical modelling is a very useful tool to predict the fire resistance of a structure, or to reproduce artificially what has happened during a real fire. SAFIR, a non linear computer code developed at the university of Liege-Belgium, is specifically written for modeling the behavior of structures subjected to fire. It allows a determination of the temperatures in the structure resulting from the fire and, in a subsequent analysis, determination of the successive positions of equilibrium of the structure until collapse. Ten steel hollow section columns filled with self-compacting concrete embedding another steel profile have been tested in the Fire Engineering Laboratory of the University of Liege - Belgium. SAFIR code has been used to simulate the thermal and structural behavior under fire conditions. A good agreement between numerical and experimental results has been obtained. This shows that SAFIR code can predict well the behavior of CFSHS columns subjected to fire. [less ▲]

Numerical analysis of stainless steel beam-columns in case of fire

in Fire Safety Journal (2012), 50

Large-Scale Fire Test of Unprotected Cellular Beam Acting in Membrane Action

in Journal of Structural Fire Engineering [=JSFE] (2011), 2(4), 259-268

This paper describes a full scale fire test performed the 27th of February 2010 on a composite floor for analysing the possibility of tensile membrane action to develop when the unprotected steel beams in ... [more ▼]

This paper describes a full scale fire test performed the 27th of February 2010 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 × 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 ▲]

Le mot du président

in Courard, Luc; Dehousse, Nicolas; Demonceau, Jean-François (Eds.) et al 300e conférence du C.E.R.E.S (2011)

On discute du rôle du CERES: essentiellement une fenêtre ouverte sur le monde pour nos chercheurs et nos étudiants, un moyen pour le département ArGEnCo de maintenir le contact avec le monde de l ... [more ▼]

On discute du rôle du CERES: essentiellement une fenêtre ouverte sur le monde pour nos chercheurs et nos étudiants, un moyen pour le département ArGEnCo de maintenir le contact avec le monde de l'entreprise. [less ▲]