Modelling thermal performance of gypsum plasterboard‐lined light timber frame walls using SAFIR and TASEF

Gypsum plasterboard is commonly used as a lining material on lightweight timber or steel framing. Gypsum contains moisture, both free and chemically bound in its crystal structure. The dehydration of the gypsum and decomposition of calcium carbonate absorb heat giving gypsum plasterboard fire resistant qualities. This paper discusses the suitability of the finite element heat transfer program SAFIR for modelling plasterboard‐lined light timber frame assemblies and its limitations. The default material properties in SAFIR for gypsum plasterboard do not give good results and ‘smoothing’ of enthalpy curves has insignificant effects on the results but substantially reduces processing time. Modelling with SAFIR gives similar results to prior modelling using the program TASEF with slight differences. Both programs give better overall results for slower developing fires and furnace tests than more rapidly growing fires. Reasonable, slightly conservative results for thermal analysis of heat transfer through the walls and into timber studs can be achieved using the parameters suggested in this paper. More sophisticated and detailed models incorporating mass transfer, effect of fasteners, gaps between lining sheets and ablation are required to achieve better comparisons. Copyright © 2010 John Wiley & Sons, Ltd.     

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

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.     

Thermal modelling of gypsum plasterboard assemblies exposed to standard fire tests

Gypsum plasterboards are widely used for compartmentation and for retarding the spread of fire in buildings. Although numerous heat transfer studies have been conducted, literature indicates there are extensive differences in the thermal properties used in these studies. Comprehensive experimental and numerical analyses have been conducted to elucidate the leading factor in the ablation of a gypsum board system when it is exposed to the standard fire resistance test. A methodology based on both simultaneous thermal analysis and computational modelling is proposed to understand the behaviour of a gypsum plasterboard when the boundary temperature increases quickly as one side of the wall is subjected to the standard ISO 834. Finally, four different wall assemblies made of a commercial fireproof plasterboard system are exposed to the standard test. The temperature on the unexposed face is examined to validate the computational model of the plasterboard. Copyright © 2015 John Wiley & Sons, Ltd.     

A model to predict fire resistance of non‐load bearing wood‐stud walls

The author has developed a series of computer models to predict the fire resistance of wood‐framed walls and floors. The models utilize two‐dimensional heat‐conduction equations and thermo‐physical property data to describe heat transfer through the assemblies. The model for wall assemblies WALL2D, the basic version of the wall model, has already been published in Fire and Materials. Recently, WALL2D has been extended to WALL2DN to analyse heat transfer through insulated walls and walls that experience openings at the joints between adjacent sheets of gypsum board. Since gypsum board shrinks at high temperatures, the joints between adjacent sheets of gypsum board open. Hot fire gases, thereby, enter the openings and heat the edge of the gypsum board and wood studs. The new model WALL2DN simulates the joint opening and describes the resultant effect of openings. The model also calculates heat transfer through insulation in the stud cavity and depicts the effect of insulation on the fire resistance of non‐load bearing wall assemblies. Insulation selected in WALL2DN is glass‐fibre insulation, rock‐fibre insulation, polystyrene foam and polyurethane foam. When walls are exposed to fire, the insulation in the cavity shrinks (and/or melts) and an empty space appears at the interface between insulation and gypsum board. The model simulates this shrinking behaviour of insulation in the cavity. Finally, the model was validated by comparing the predicted results to those from full‐scale standard fire‐endurance tests. Copyright © 2003 John Wiley & Sons, Ltd.     

Predicting the thermal response of gypsum board subjected to a constant heat flux

Models are available to predict the fire‐resistance ratings of wood‐frame assemblies protected by gypsum board. These models have been developed to predict the performance of assemblies exposed to a standard fire test in which temperatures increase monotonically. In an ongoing effort to model the fire resistance of light‐frame wood floor assemblies, in this study, a number of improvements over past heat transfer models have been made in an attempt to simulate assembly performance in any arbitrary fire exposure. For this purpose, the heat transfer analysis has been coupled with a mass transfer analysis. The calcination of gypsum board and pyrolysis of wood are now modelled using an Arrhenius expression. In order to evaluate the accuracy of the model, a series of cone calorimeter experiments have been conducted in an effort to generate experimental data under well‐defined boundary conditions. Comparisons between test results and the predictions from a one‐dimensional heat and mass transfer analysis are encouraging with excellent agreement in predicting the point at which gypsum board is fully calcinated. A lack of material property data, particularly the permeability of gypsum board, remains a limiting factor in further improvement of the accuracy of the model. Copyright © 2008 John Wiley & Sons, Ltd.     

Computational stochastic heat transfer with model uncertainties in a plasterboard submitted to fire load and experimental validation

The paper deals with probabilistic modeling of heat transfer throughout plasterboard plates when exposed to an equivalent ISO thermal load. The proposed model takes into account data and model uncertainties. This research addresses a general need to perform robust modeling of plasterboard‐lined partition submitted to fire load. The first step of this work concerns the development of an experimental thermo physical identification data base for plasterboard. These experimental tests are carried out by the use of a bench test specially designed within the framework of this research. A computational heat transfer model is constructed using data from the literature and also the identified plasterboard thermophysical properties. The developed mean model constitutes the basis of the computational stochastic heat transfer model that has been constructed employing the nonparametric probabilistic approach. Numerical results are compared to the experimental ones. Copyright © 2008 John Wiley & Sons, Ltd.     

Elevated temperature thermal properties of advanced materials used in LSF systems

Lightweight cold-formed steel (CFS) construction solutions are increasingly adopted in low and mid-rise buildings. Many different materials are used to construct CFS wall systems, without a full understanding of their thermal properties. For many of these materials, only ambient temperature thermal properties are available from their manufacturers. This creates difficulty in classifying the materials for use at elevated temperatures. In this study, a series of elevated temperature thermal property tests to measure specific heat, thermal conductivity, and mass loss was conducted for a range building materials from wallboards, insulation, and phase-change materials (PCMs), used in Australia and several other countries. Simultaneous Thermal Analyser and Laser Flash Apparatus were used to determine the elevated temperature thermal properties of the selected materials, gypsum plasterboard, PCM incorporated gypsum plasterboard, magnesium sulphate board, fibre cement board, cellulose insulation, vacuum insulation panel, microencapsulated paraffin PCM, and bio-based PCM. Their elevated temperature thermal properties are presented in this article, which also includes analyses of their chemical composition and associated chemical reactions at elevated temperatures. These results can be used in the selection of suitable energy-efficient and fire-resistive materials, and in heat transfer modeling to identify wall configurations with increased fire resistance and energy efficiency.     

Thoughts and observations on fire‐endurance tests of wood‐frame assemblies protected by gypsum board

Forintek Canada Corp. participated in a series of collaborative research projects with the National Research Council Canada and other organizations to determine fire‐resistance ratings for wood‐frame assemblies used in the construction of Canadian housing and small buildings. Over the course of those studies, Forintek's scientists observed a large number of full‐scale fire‐endurance tests on walls lined on both faces with gypsum board and floor assemblies with gypsum‐board ceilings. Those observations have given Forintek's researchers unique insights into the fire performance of wood‐frame assemblies and fire‐endurance testing. Those insights are the subject of this paper. Copyright © 2002 John Wiley & Sons, Ltd.     

Gypsum board failure model based on cardboard behaviour

This study aims to analyse the importance of gypsum plasterboard cardboard for fire resistance. A new hypothesis considering the failure based on the cardboard degradation is defined. This hypothesis comes from the thermal analysis of gypsum and cardboard performed in the simultaneous thermal analysis apparatus. Simultaneous thermal analysis results also allow defining the dehydration process of the gypsum. A numerical model that considers gypsum dehydration and the failure hypothesis has been developed by using Fire Dynamic Simulator. This numerical model is validated against 6 fire resistance tests. Results show that we can appropriately tune the numerical model (for predicting time to failure) based on the thermal properties of cardboard.     

The discrepancies in energy balance in furnace testing,a bug or a feature?

The paper aims to explain the differences found in the heat release rate measurements in a large sample of standard fire tests (EN 1363-1). A total of 379 tests of vertical assemblies was investigated, all performed in furnace SPARK of the ITB Fire Testing Laboratory, in 2015-2018. The assemblies were subdivided into two groups—wall assemblies and fire-rated doors. These assemblies were also compared with the results of the test of a wall built with aerated autoclaved concrete blocks that was considered as the benchmark test. It was observed that walls built with highly insulated sandwich panels require less heat to maintain standard thermal exposure conditions (20%-30% less) than their counterparts built from gypsum plasterboard or aluminium and fire-rated glass. In case of doors, it was observed that combustible samples required significantly less heat than the benchmark case (40%-70% less), which indicates that the combustion of the sample inside of the furnace was an additional, significant source of heat release, that may skew the qualitative assessment of their performance in fire. A more in-depth discussion of the results is provided, with some ideas on the direction of further developments in fire testing.     

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

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 apparent thermal properties. The approach is shown to be very effective in simulating temperature development in timber members subject to parametric design fires. The models developed are benchmarked against experiments conducted in the 1990s by SP Trätek. Predictably, a number of the heat generation parameters adopted are shown to depend on the fire dynamics considered. However, recommended parameters are given that provide an acceptable level of accuracy for most design purposes. Copyright © 2012 John Wiley & Sons, Ltd.     

Calculation of thermal conductivity of gypsum plasterboards at ambient and elevated temperature

Plasterboard often protects steel structures of buildings because it conducts heat slowly and absorbs the heat of the fire by its volumetric enthalpy. The most important property governing the heat transfer is the thermal diffusion. This property depends on the density, specific heat and thermal conductivity. The first two can be calculated based on the mass composition of the board. The thermal conductivity is more difficult to derive since it is a directional property. This paper will focus on the calculation of the thermal conductivity at ambient and elevated temperatures. It is shown that the thermal conductivity of gypsum plasterboard (i.e. a porous medium) can be assumed to be a three‐phase system. Plasterboard consists of a solid phase and a water/air mix in the voids. The differences between different theoretical equations for both dry and moistured plasterboards are presented. The equation proposed by Zehner and Schlunder (Chem. Ing.‐Tech. 1972; 44 (23):1303–1308) with shape‐factor C of 5 gave good agreement with experimental data of the different boards. Furthermore, the influence of the composition of the boards on the thermal conductivity is investigated. This has an influence, especially since the composition is also related to its moisture content. Regression analysis points out that the moisture content depends only on the gypsum content. A value of 2.8% absorbed water on the mass of gypsum is found, and this water plays an important role in the thermal conductivity of plasterboard at ambient temperature. Finally, the thermal conductivity of board at elevated temperature is computed. A close fit between computed and experimental values derived from literature is found. Copyright © 2009 John Wiley & Sons, Ltd.     

Fire performance of non-load-bearing double-stud light steel frame walls: Experimental tests,numerical simulation,and simplified method

Double-stud light steel frame (LSF) walls provide an enhanced insulation performance when exposed to fire conditions. However, the behavior of different configurations of such assemblies under fire is not well understood. Thus, this study aimed to assess the fire resistance of non-load-bearing double-stud LSF walls subjected to ISO834 standard fire. The walls were lined with one or two type F gypsum plasterboards on each side, using cavity uninsulated or insulated with ceramic fiber. The experimental tests revealed that a wider cavity slows the heat transfer through the cross-section, delaying the temperature rise on the unexposed surfaces. The use of ceramic fiber insulation substantially increases the fire resistance of the wall and when the cavity is partially filled with this material, if the blanket is placed towards the exposed side, enhanced insulation fire resistance is achieved. Based on the finite element method, a numerical validation was conducted using a special hybrid approach that used experimental temperature values inside the cavities or insulation blankets. This approximation was essential to improve the numerical results. Also, the employment of an air layer, located at specific regions of the models, helped to improve the numerical results, introducing an extra thermal resistance. A new simplified approach was proposed based on the improved design model available in the literature, and the results obtained are consistent with the experimental results. The predicted insulation fire resistance of the numerical and simplified methods agreed well with the experimental results and useful information is supplied to support further numerical and experimental studies.     

A model for predicting heat transfer through gypsum-board/wood-stud walls exposed to fire

To facilitate the development of cost-effective and flexible design options there is a need to develop models to predict the fire resistance of wood-frame building assemblies. Such assemblies often derive much of their fire resistance from a protective membrane composed of gypsum board. A simple two-dimensional computer model is presented to predict heat transfer through gypsum-board/wood-stud walls exposed to fire. Input data for the thermophysical properties of gypsum board were measured exploying standard bench-scale tests. Input data for wood were selected from the literature. Small-and full-scale fire resistance tests were conducted on gypsum-board/wood-stud wall assemblies to provide data for the validation of the model. The model is shown to predict heat transfer through these walls rather well.     

Fire performance of closed‐cell charring insulation materials in plasterboard‐insulation assemblies

This paper presents an experimental study on the fire performance of two types of plastic charring insulation materials when covered by a plasterboard lining. The specific insulation materials correspond to rigid closed‐cell plastic foams, a type of polyisocyanurate (foam A) and a type of phenolic foam (foam B), whose thermal decomposition and flammability were characterised in previous studies. The assemblies were instrumented with thermocouples. The plasterboard facing was subjected to constant levels of irradiation of 15, 25, and 65 kW m^?2 using the heat‐transfer rate inducing system. These experiments serve as (1) an assessment of the fire behaviour of these materials studied at the assembly scale and (2) an identification of the fire hazards that these systems pose in building construction. The manifestation of the hazards occurred via initial pyrolysis reactions and release of volatiles followed by various complex behaviours including char oxidation (smouldering), cracking, and expansion of the foam. Gas‐phase conditions may support ignition of the volatiles, sustained burning, and ultimately spread of the flame through the unexposed insulation face. The results presented herein are used to validate the insulation “critical temperature” concept used for a performance‐based methodology focused on the selection of suitable thermal barriers for flammable insulation.     

Thermal conductivity of gypsum boards beyond dehydration temperature

The thermal conductivity of gypsum plasterboard at temperatures beyond its dehydration/calcination temperature is, besides the effective heat capacity, the main parameter defining the increase in heat transfer when the board is submitted on one side to a strongly transient temperature boundary condition. The present study investigates the significant rise in thermal conductivity of dehydrated gypsum plaster board between 200 and 800 °C, reaching the initial hydrated value of 0.3 W/(m·K). It is shown that the main reason for this increase is independent of radiative and convective heat transfers and only due to an enhancement of the conduction between the single crystals induced by an effect similar to sintering. Copyright © 2014 John Wiley & Sons, Ltd.     

The effects of subfloor and insulation type and thickness on the fire resistance of small‐scale floor assemblies

This paper discusses the results of 28 fire resistance tests conducted on unloaded insulated and non‐insulated, small‐scale frame floor assemblies using the ULC/ASTM fire exposure time–temperature curve. The frames used include either solid wood joist, wood I‐joist, parallel‐chord wood truss or steel C‐joists. Temperatures were measured throughout the assemblies. All frames were protected on the fire‐exposed side by Type X gypsum board, 16 mm thick. Parameters investigated in this study include the effects of subfloor type (plywood and oriented strand board), insulation type (glass, rock and cellulose) and insulation thickness (90 mm, 180 mm and full cavity). The impact of these parameters on the fire resistance performance of small‐scale floor assemblies is discussed. Copyright © 2000 Crown in the right of Canada. Published by John Wiley & Sons, Ltd.     

Thermal performance of load‐bearing walls made of cold‐formed hollow flange channel sections in fire

Typical load‐bearing light gauge steel frame (LSF) walls are made of conventional lipped channel section studs and gypsum plasterboards. Current research at the Queensland University of Technology is investigating the effects of using new thin‐walled stud sections on the fire‐resistant rating of LSF walls, in particular, the use of hollow flange channel (HFC) sections. A sound knowledge on the thermal performance of these LSF walls is essential, but expensive and time‐consuming nature of fire tests has acted as a barrier. In this study, finite element models were developed to predict the thermal performance of load‐bearing LSF walls made of HFC section studs exposed to fire on one side. The developed models were validated using the results of five full‐scale standard fire tests of LSF walls. They were then extended to perform a parametric study where the effects of stud dimensions, geometries, spacings and wall configuration were evaluated. The hot and cold flange time‐temperature profiles of HFC studs were developed as a function of the aforementioned parameters, which can be used to predict the fire resistance ratings of LSF walls. This paper presents the fire tests, and the details of the developed finite element models and the thermal performance results of LSF walls made of HFC studs. Copyright © 2015 John Wiley & Sons, Ltd.     

Influence of gypsum board type (X or C) on real fire performance of partition assemblies

This paper compares the responses of wall‐size partition assemblies, composed of either type X or type C gypsum wallboard panels over steel studs, when each was exposed to an intense room fire. The exposures lasted from the time of ignition to beyond flashover. Heat flux gauges provided time histories of the energy incident on the partitions, while thermocouples provided data on the propagation of heat through the partitions and on the progress toward perforation. Visual and infrared cameras were used to image partition behaviour during the fire exposure. Contraction of the seams of the two types of assemblies occurred under similar thermal conditions on the unexposed surface. However, there were noticeable differences in cracking behaviour. Reduced scale experiments were performed in conjunction with the real‐scale fire tests to provide insight into the contraction and cracking behaviour of the different gypsum board types. Results obtained from these experiments are discussed. Copyright © 2006 John Wiley & Sons, Ltd.     

Fire performance of gusset connections in glue-laminated timber

This paper describes a comprehensive experimental investigation of the fire performance of nailed gusset connections between large glue-laminated timber members. Both plywood and steel gusset plates were investigated with a range of loaded and unloaded test methods. The principal conclusions are that unprotected gussets have poor fire performance, but that a layer of solid wood or gypsum plasterboard will provide at least one hour of fire protection to typical joints.