Modelling heat and moisture transfer in timber exposed to fire

Pečenko, Robert; Svensson, Staffan; Hozjan, Tomaž

doi:10.1016/j.ijheatmasstransfer.2015.04.024

Cited by 21 publications

(23 citation statements)

References 12 publications

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“…In Equation (3) h b and h v represent the specific enthalpies of bound and vapour water while h vb = h b − h v is the specific enthalpy of the transition from the bound water phase to the water vapour. The last term in Equation 3is obtained as in Pečenko et al (2015). The sorption rate in terms of concentrations is defined asċ…”

Section: Short Description Of the Multi-fickian Hygro-thermal Model Amentioning

confidence: 99%

Moisture-induced stresses in large glulam beams. Case study: Vihantasalmi Bridge

Fortino

Hradil

Metelli

2019

Wood Material Science & Engineering

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The structural performance of timber elements may depend on the environmental conditions and in particular on the cyclic variations of the moisture content. Moisture gradients in the sections of the structural elements can produce additional stresses, the so-called moisture-induced stresses (MIS), which can cause the formation of cracks and delamination in wooden components. In order to achieve a reliable evaluation of the safety level of timber structures, the present paper proposes a numerical methodology to evaluate the MIS in glulam beams of timber bridges under Northern European climates and mechanical loads. A hygro-thermal multi-Fickian model for prediction of moisture content, relative humidity and temperature in wood is sequentially coupled with an orthotropic-viscoelastic-mechanosorptive model for calculation of wood stresses. Both models were developed by some of the authors in Abaqus FEM code in previous works and their coupling is used here to analyse the hygro-thermo-mechanical response of a glulam beam of Vihantasalmi Bridge in Finland under bending loads. Both perpendicular and parallel to grain MIS in a beam section sheltered from rain are evaluated during a 10-year analysis and conclusions on the crack risk related to these stresses are given.

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Section: Short Description Of the Multi-fickian Hygro-thermal Model Amentioning

confidence: 99%

Moisture-induced stresses in large glulam beams. Case study: Vihantasalmi Bridge

Fortino

Hradil

Metelli

2019

Wood Material Science & Engineering

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“…Despite numerous empirical expressions to determine charring depth, their range of application for assessing the fire resistance of timber elements is usually limited to cases with simple geometry, standard fire exposure or precisely defined non-standard fires and to only a particular wood species under investigation. The researchers tried to improve the mentioned deficiency by using heat (Fragiacomo et al 2012;Frangi et al 2008;Tsai et al 2013) and heat-mass transfer numerical models (Pečenko et al 2015). In these models, the charring depth is determined based on the calculated temperature isotherm, often referred to as the char front temperature, in a timber cross-section.…”

Section: Introductionmentioning

confidence: 99%

“…The basis for the development of the new numerical model presents the coupled heat transfer and multiphase mass transfer model given in Pečenko et al (2015). The model is based on the bound water diffusion in wood cell walls, the diffusion and convection of water vapor and air in lumens, and precise formulation of the interaction between the bound water and the water vapour, known as sorption.…”

Section: Introductionmentioning

confidence: 99%

“…Compared to other coupled heat-mass models (Younsi et al 2006(Younsi et al , 2007, this model presented a very accurate description of the heat-mass transfer in wood. However, as already described, the main disadvantage of the model (Pečenko et al 2015) was simple estimation of charring, determined from the temperature isotherm (300°C ), which is suitable only for standard or similar fire exposure. Therefore, to make a transition to natural fire, the model (Pečenko et al 2015) is upgraded in the presented paper, to couple the process of heat-mass transfer with the process of pyrolysis.…”

Section: Introductionmentioning

confidence: 99%

“…However, as already described, the main disadvantage of the model (Pečenko et al 2015) was simple estimation of charring, determined from the temperature isotherm (300°C ), which is suitable only for standard or similar fire exposure. Therefore, to make a transition to natural fire, the model (Pečenko et al 2015) is upgraded in the presented paper, to couple the process of heat-mass transfer with the process of pyrolysis. The coupling arises from the combination of pyrolysis reaction products (gases) with the mass transfer in timber elements.…”

Section: Introductionmentioning

confidence: 99%

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A novel approach to determine charring of wood in natural fire implemented in a coupled heat-mass-pyrolysis model

Pečenko

Hozjan

2020

Holzforschung

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The paper presents a novel approach to determine charring of wood exposed to standard and natural fire that is based on a new numerical model named PyCiF. The new model couples an advanced 2D heat-mass model with a pyrolysis model. A new charring criterion based on a physical phenomenon is implemented in the PyCiF model to determine charring of wood. This presents the main advantage of the new PyCiF model in comparison to common modelling approaches, which require an empirical value of the charring temperature that is often called the char front temperature. The fact that the char front temperature is not an explicit value as assumed by the isotherm 300 °C is advantageously considered in the presented approach where an assumed empirical value of the char front temperature is not directly required to determine the thickness of char layer. The validation of the PyCiF model against experimental results showed great model accuracy, meaning that the model is appropriate for the evaluation of charring depths of timber elements exposed to the standard fire as well as the natural fires. Additionally, as shown in the case study, the presented approach also enables to determine the char front temperature for various natural fire exposures. This will be especially important for the upgrade of the new design methods for fire safety of timber elements exposed to natural fire given in the various design codes such as Eurocode 5.

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