Thermal model for charring rate calculation in wooden cellular slabs under fire

Wood is a natural and traditional building material, as popular today as ever, and presents advantages. Physically, wood is strong and stiff, but compared with other materials like steel is light and flexible. Wood material can absorb sound very effectively and it is a relatively good heat insulator. But dry wood burns quite easily and produces a great deal of heat energy. The main disadvantage is the high level of combustion when exposed to fire, where the point at which it catches fire is from 200–400°C. After fire exposure, is need to determine if the charred wooden structures are safe for future use. Design methods require the use of computer modelling to predict the fire exposure and the capacity of structures to resist those action. Also, large or small scale experimental tests are necessary to calibrate and verify the numerical models. The thermal model is essential for wood structures exposed to fire, because predicts the charring rate as a function of fire exposure. The charring rate calculation of most structural wood elements allows simple calculations, but is more complicated for situations where the fire exposure is non-standard and in wood elements protected with other materials. In this work, the authors present different case studies using numerical models, that will help professionals analysing woods elements and the type of information needed to decide whether the charred structures are adequate or not to use. Different thermal models representing wooden cellular slabs, used in building construction for ceiling or flooring compartments, will be analysed and submitted to different fire scenarios (with the standard fire curve exposure). The same numerical models, considering insulation material inside the wooden cellular slabs, will be tested to compare and determine the fire time resistance and the charring rate calculation

Cellular slabs with and without insulation submitted to fire conditions

The wooden cellular slabs are lightweight structures, easy to assemble, and with excellent architectural features, as good thermal and acoustic conditions. The wooden cellular slabs with perforations are typical and very common engineering solutions, used in the ceiling or flooring to improve the acoustic absorption of compartments, and also have a good insulation and relevant architectonic characteristics. However, the high vulnerability of wooden elements submitted to fire conditions requires the evaluation of its structural behaviour with accuracy. The main objective of this work is to present a numerical model to assess the fire resistance of wooden cellular slabs with different perforations. Also the thermal behaviour of the wooden slabs will be compared considering material insulation inside the cavities. The time-temperature history and the residual cross-section of wooden slabs were numerically measured and analysed

Computational model for W-W-W connections at ambient and high temperatures

The aim of this work is to present an approach for wood‐wood‐wood (W‐W‐W) connections design in double shear at ambient and high temperatures, using dowelled connectors. For each situation, all calculations will be performed to determine the cross‐section and the number of fasteners. A procedure will be presented to calculate the load carrying capacity per shear plane and per steel fastener, using a glued laminated in birch W‐W‐W timber GL28h.info:eu-repo/semantics/publishedVersio

Behaviour of cellular steel beams at ambient and high-temperature conditions

New developments in building construction have been observed to attain sustainable design criteria and the efficient use of raw materials, as steel is an example. This led to an increase in recent research on the optimization of geometric configurations of web-opening steel sections to meet cost-effectiveness in structural design. Improvement of the design method for perforated unrestrained steel beams to assess their behaviour under lateral torsional buckling (LTB) is still an ongoing issue for scientists and designers alike. In this article, cellular beams bound to instability were studied analytically by Eurocode and numerically by the finite element method to investigate their behaviour at ambient and elevated temperatures due to fire. The analysis encompasses the effect of the coupling and the endplates' thickness on the cellular beams' collapse strength considering the initial geometric imperfections and material nonlinearities. A parametric study including changing temperature, crosssection geometry, and web aperture configurations was done for beams subjected to uniform bending and distributed load. The analyses depicted the following failure modes: LTB and LTB+ plastification of the two Tsection (P-2 T) for end moment load and yielding of top tee section's flange (B-1 T), P-2 T, web post-buckling (WPB), Vierendeel mechanism (VM) and LTB for a distributed load. Combined failure modes such as LTB + WPB, LTB + VM and LTB + VM + WPB have also been observed. Buckling curves for cellular beams were assessed by comparing FE reduction factors with those of the buckling curve recommended by Eurocode 3 for equivalent solid steel beams. A new proposed formula for the plateau length of the LTB curves was obtained, based on the mean squared error method (MSE) between the numerical results and Eurocode formulae. The comparison between the numerical and the simplified design method predicted results shows that the proposed formulae have reduced the discrepancy and improved the LTB curve to better assess the cellular beams behaviour.The Ministry of Higher Education and Scientific Research, MESRS, of Algeria, is gratefully acknowledged for the PhD grant funding support: ref. 714/PNE/Doctorant/Portugal/2019-2020.info:eu-repo/semantics/publishedVersio

Investigation of residual stresses on the fire resistance of unrestrained cellular beams

It is being a common engineering practice to use steel beams with web openings in buildings requiring long spans, besides giving an important additional advantage of allowing services through instead of underneath the beams. The presence of these openings is penalizing the carrying capacity at ambient temperature and in the case of fire due to large cells and double nonlinearity geometric and material a complex behaviour take place. In this study, numerical models for beams having closely spaced large openings are simulated with ISO834 fire loading including both nonlinearities cited above in the primal investigation. Followed as a second investigation, is the effect of residual imperfections added to the numerical model mentioned above and simulated for different diagrams as presented within updated literature. All simulations were done using the finite element software ANSYS, to analyse the results captured for lateral torsional buckling (LTB) behaviour in terms of vertical and lateral displacement, von Mises stresses for different sections at ambient and fire conditions. For this parametric study, the change in cross-section geometries, opening spacing, beam length on the LTB of cellular beams is analysed.info:eu-repo/semantics/publishedVersio

Simulation numerique du comportement non-lineaire des portiques métalliques en situation d’incendie

Pour des raisons pratiques d’exploitation et de durabilité, les bâtiments industriels, sont dans la majorité des cas conçu en charpente métallique. Cependant le matériau acier quoi que ductile, il reste vulnérable aux excès de températures. Les récents événements d’incendies concernant les structures et bâtiments industriels de Sonatrach, à Alger dans une zone urbaine ou à Skikda dans une zone industrielle, nous rappellent le danger réel et le risque potentiel des incendies. Les nouvelles normes Européennes définissent des exigences actives et passives concernant le comportement au feu des bâtiments industriels. L’objectif de ce travail concerne l’étude du comportement non-linéaire des structures industrielles en acier selon plusieurs scénarios de feu. L’analyse numérique par la MEF et utilisant le logiciel ANSYS est considérée afin d’évaluer la résistance de ces structures et d’optimiser leur protection au feu. Une analyse, utilisant les non linéarités géométrique et matérielle, est conduite avec une variation progressive des températures jusqu’à la ruine. Différents taux de chargement ainsi que différents scénarios de feu seront utilisés pour évaluer la température critique ainsi que les déplacements des portiques en fonction de l’évolution de la température

Etude par simulation numérique du comportement des portiques métalliques en situation d’incendie

Les structures en portiques métalliques à double versants sont largement utilisées dans les bâtiments industriels pour des raisons pratiques d’exploitation, de durabilité et de rentabilité. Cependant le matériau acier quoi que ductile, il reste vulnérable aux excès de températures. Les récents événements d’incendies concernant les structures et bâtiments industriels de Sonatrach, à Alger dans une zone urbaine ou à Skikda dans une zone industrielle, nous rappellent le danger réel et le risque potentiel des incendies. Les nouvelles normes Européennes définissent des exigences actives et passives concernant le comportement au feu des hangars industriels. L’objectif de ce travail est d’étudier, par des simulations numériques, le comportement des portiques métalliques à double versants sous différents scénarios d’incendie. L’analyse numérique par la MEF et utilisant le logiciel ANSYS est considérée afin d’évaluer la résistance de ces structures et de rationaliser leur protection au feu. Une analyse, utilisant les non linéarités géométrique et matérielle, est conduite avec une variation progressive des températures jusqu’à la ruine. Différents taux de chargement ainsi que différents scénarios de feu seront utilisés pour évaluer la température critique ainsi que les déplacements des portiques en fonction de l’évolution de la température. Les résultats du modèle numérique sont comparés à ceux calculés par les méthodes simplifiées de l’Eurocode 3info:eu-repo/semantics/publishedVersio

On the behaviour of structural steel beams under natural compartment fire

Fire is an extreme action, to which a steel structure may be submitted, and therefore, must be designed to resist. Traditionally, the fire resistance of structural steel beams has been determined in standard fire tests, with the temperature-time curveISO834representing more severe heating conditions compared to that which occurs in many typical natural fire compartments.Thereforeto design a steelstructure safely and economically, it is necessary to calculate temperature distribution in steel beamsunder natural fire. In this paper, the temperature profiles in a steel beams under natural fire arestudied first, using spread-sheets written by authorsand compared to standard fire. Secondly, twoCardington compartment corner office tests are highlighted,and analysis of primary and secondary steel beamsis presented.Simple theoretical natural fire models based on Eurocode EN 1991-1-2 parametric compartment fire are used and a comparison is made using the experimental results from tests conducted at Cardington research centre, UK. Compartment temperatures and cross-section temperature distribution respectively demonstrates that analytical fire models and experimental results are in good agreement in the case of timber cribs fire load

Finite element investigation on the behaviour of structural steel beams subjected to standard & parametric fire

This paper intends to present an investigation of the behaviour of steel beams under high temperatures rise due to fire using finite elements simulations with ANSYS software. Cases of study for solid as well as open web beams are considered and take into account uniform and transient temperature rise, material and geometric non-linear behaviour. Input fire scenarios are standard temperature-time curve ISO834 and parametric compartment fire model based upon Eurocode EN 1991-1-2. For the latter a comparison is made using the experimental results from BRE-Cardington tests data. Thermal and mechanical analysis is done using the effect of temperature dependent material properties and the Eurocode recommendations in estimating reduction mechanical steel properties. Three types of cellular beams are studied and the number of cells is shown to be critical for their behaviour under fire conditions. Results are related to temperature profiles in steel beam cross-sections, variation of displacements with respect to temperature change and critical temperatures.info:eu-repo/semantics/publishedVersio

Renforcement des sols par nappes synthetiques : influence de la flexibilite et du frottement des inclusions

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc