Comparison between the charring rate model and the conductive model of Eurocode 5

Cachim, Paulo; Franssen, Jean‐Marc

doi:10.1002/fam.985

Cited by 39 publications

(24 citation statements)

References 10 publications

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“…In an earlier publication, the author proposed an MCM for softwood timber on the basis of the principles outlined in the research by König and on EN 1995‐1‐2 specific heat modifications proposed by Cachim and Franssen . The MCM was derived using numerical calibrations of a fire load ( q td ) and heating rate (Γ) dependent modification factor and the depths of char present in parametric design fires.…”

Section: Background Theorymentioning

confidence: 99%

Predicting the thermal response of timber structures in natural fires using computational ‘heat of hydration’ principles

Hopkin¹

2012

Fire and Materials

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The thermo‐physical response of timber structures in fire is complex. For this reason, debate still exists today as to the best approaches for simulating thermal response in fire using tools such as finite element analysis (FEA) modelling. Much of the debate is concerned with the thermal properties of timber, for example, conductivity, specific heat and density, at elevated temperature and how such properties should be implemented or interpreted in numerical calculations. For practitioners intending to use modelling as a fire design tool for timber buildings, guidance exists on the thermal properties of softwood in Annex B of EN 1995‐1‐2. These properties are limited for use under standard fire exposure conditions because of the way in which they were derived from calibration against focussed test data. As a result, they cannot be applied to non‐standard fires, which are more representative of real fires due to a combination of varying heating rates and the decay phase of fire development. The limitations of the standard fire test (and associated curve) are widely understood. As a result, much recent structures in fire research has focussed on the ‘performance based design’ of buildings subject to increasingly realistic fire conditions. Such an approach allows engineers to quantify the level of safety that can be achieved in a building should a fire occur. In addition, the design of buildings to withstand fires proportionate to the risks foreseen and also the geometry present results in better value buildings that are inherently more robust. For the same approaches and associated benefits to be realised for timber buildings, then a number of barriers must be overcome. The most obvious of these is engineers' ability to determine timber structure temperatures as a result of fires other than the standard fire curve. This however presents a number of challenges. Upon heating, the moisture bound within begins to evaporate, volatiles begin to flow from the heated surface and char forms. The rate of which these behaviours occur and the nature of the char that forms depends on a number of factors, but most notably the rate of heating. Upon cooling, the timber member continues to generate heat energy as the surface oxidises. As a result, any models intended to simulate temperature development must consider the relationship not only between temperature and thermo‐physical characteristics but also between heating rate and the process of heat generation. Many models have been developed for this purpose; however, they are extremely complex and are some way from being ready for implementation as design tools. This paper proposes implementing ‘heat of hydration’ routines, intended for the curing of concrete structures, to simulate the heating and cooling process in timber structures. Such routines are available in many commercial FEA software packages. The adoption of the hydration routines allows the heat generation process, as a result of oxidation, to be considered in parallel with solid phase heat transfer using ap...

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Section: Background Theorymentioning

confidence: 99%

Predicting the thermal response of timber structures in natural fires using computational ‘heat of hydration’ principles

Hopkin¹

2012

Fire and Materials

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“…Different proposals can be found in the literature for the variation of thermal properties with temperature (e.g. [1,3,4,[6][7][8]). Such variation depends on the fire curve, and many proposals such as the Eurocode 5 one refer to ISO fire exposure [20].…”

Section: Thermal Analysismentioning

confidence: 99%

“…Different proposals can be found in literature for the variation of thermal and mechanical properties of wood with temperature (e.g. [1][2][3][4][5][6][7][8]). Several variables affect the change of material properties such as wood species, moisture content, fire conditions, stress direction with respect to the grain and level of applied load.…”

Section: Introductionmentioning

confidence: 99%

Predicting the fire resistance of timber members loaded in tension

et al. 2012

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SUMMARY The paper presents a numerical model for predicting the fire resistance of timber members. Fire resistance is evaluated in a two‐step process implemented in the Abaqus finite element code: first, a time‐dependent thermal analysis of the member exposed to fire and then a structural analysis under a constant load are performed. The structural analysis considers the reduction in mechanical properties (modulus of elasticity and strength) of timber with temperature. The analysis terminates when the member can no longer redistribute stresses from the hottest to the coldest parts, leading to structural failure. The model was used to simulate fire tests carried out on specimens made from laminated veneer lumber loaded in tension. Experimental data in terms of temperature, charring depth, displacement and failure time were compared with the numerical results obtained by assuming the thermal properties and degradation of mechanical properties with temperature as suggested by Eurocode 5, showing an overall acceptable approximation. The fire resistance of the timber member was then predicted depending upon the applied tensile loads using the numerical model and analytical formulas. The proposed finite element model can be used to predict the fire resistance of timber structures as an alternative to expensive and complicated experimental tests. Copyright © 2012 John Wiley & Sons, Ltd.

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“…The properties for the polymer foam insulation were taken from Hobbs and Lemmon for PUR 25. For OSB, density‐ and moisture‐dependent specific heat for timber, proposed by Cachim and Franssen 23, were adopted, with appropriate density and moisture content.…”

Section: Impact Of Plasterboard Properties On Temperature Developmmentioning

confidence: 99%

“…The final plasterboard property data set studied includes those calibrated previously in Section 4 case 4.3. The use of timber properties from EC5‐1‐2 and those proposed by Cachim and Franssen 23, although limited to standard fire exposure due to the method of derivation, are deemed suitable for this analysis for two reasons. First, the experimentally measured timber temperatures remained low, and, second, the heating rate and the overall severity of the fire were not significantly different from that of the standard fire curve.…”

Section: Simulation Of Temperature Development In Real Firesmentioning

confidence: 99%

A numerical study of gypsum plasterboard behaviour under standard and natural fire conditions

Hopkin

Lennon²,

El-Rimawi

et al. 2011

Fire and Materials

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SUMMARY Gypsum plasterboards are the most widely used passive fire protection for timber structures, especially in the case of light timber frame construction. Understanding the complex thermo‐physical behaviour of plasterboard at elevated temperature is vital in the performance‐based design of any structure adopting gypsum as passive fire protection (PFP). Numerous heat transfer studies have been conducted over the years where attempts have been made to simulate the fire performance of gypsum‐protected assemblies, subject to standard fire exposure. However, contradictory thermal properties for gypsum plasterboard are apparent throughout. As a result, it is unclear from a practitioner's perspective as to which studies represent reasonable properties for design purposes. In recognition of this the authors present a numerical study highlighting the consequences of adopting many of the differing property sets available in the literature, the sensitivity of temperature development resulting from deviations from the assumptions that underpin such properties, and the consequences of adopting plasterboard properties derived from standard fire tests, in natural fire situations. The study presents heat transfer simulations conducted using the finite element software TNO DIANA coupled with both laboratory and natural fire tests conducted on Structural Insulated Panels (SIPs) and Engineered Floor Joists (EFJs). It is found from this study that plasterboard properties are highly sensitive to the assumed free and chemically bound moisture contents. Minor percentage changes are shown to have a significant influence on the temperature development of SIPs exposed to standard furnace fires, while some of the most accepted plasterboard properties available in the literature are found, in some cases, to be non‐conservative when adopted in simulations of SIPs. More interestingly, it is also found that the properties of plasterboard available in the literature, largely derived from standard fire tests, are not independent of the heating rate. As a result, when such properties are applied to natural fire problems significant inaccuracies can occur. Copyright © 2011 John Wiley & Sons, Ltd.

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Comparison between the charring rate model and the conductive model of Eurocode 5

Cited by 39 publications

References 10 publications

Predicting the thermal response of timber structures in natural fires using computational ‘heat of hydration’ principles

Predicting the thermal response of timber structures in natural fires using computational ‘heat of hydration’ principles

Predicting the fire resistance of timber members loaded in tension

A numerical study of gypsum plasterboard behaviour under standard and natural fire conditions

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