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.     

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.     

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.     

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 protection of wood by different gypsum plasterboards

Cone calorimeter tests were performed on specimens made of pieces of wood and pieces of gypsum plasterboards protecting the wood against the heat. The thermal behaviour of the gypsum plasterboards of different origin was studied by determining the time to onset of charring and the charring rate of wood. The specimens were exposed to a constant heat flux of 50 kW/m². The test results show that the time to onset of charring is more dependent on the board thickness than the area weight of the boards. The charring rate is fairly well predicted both by the board thickness and area weight, the latter being slightly better as a prediction parameter. The mechanical board properties needed in order to fully understand the fire protection from gypsum plasterboards were not studied in this investigation. Copyright © 1999 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.     

Performance of wood stud shear walls exposed to fire

This paper presents the results of seven full‐scale fire resistance tests conducted on load‐bearing gypsum board protected, wood stud shear wall assemblies. The experimental studies were conducted to determine the effects of placement of shear membrane and type of insulation on the fire resistance of such assemblies. Details of the results, including the temperatures and deflections measured during the fire tests, are presented. Results from the studies indicate that the placement of shear membrane and insulation type significantly influence the fire resistance of such wood stud shear wall assemblies. Copyright © 2000 Crown in the right of Canada.     

Advances in modelling heat transfer through wood framed walls in fire

Described in this paper are advances made in modelling heat transfer through wood framed walls in fire. Previously unpublished experimental results are also given. This type of modelling is used for the determination of the performance of fire safety systems, such as wood framed wall barriers, in accordance with new performance‐based building regulations being introduced around the world. Advances include a discrete modelling method for radiative heat transfer in cavities with re‐entrant corners and gaps formed by the shrinkage of stud cross‐sections. It has been shown that the formation of the gaps can prevent temperatures rising in the fire side of studs by as much as 100–200°C. A simple means of modelling heat transfer by the movement of moisture and vapour, involving the modification of conductivity values has been developed. Sloughing of gypsum board sheets has been satisfactorily modelled assuming that a sheet sloughs when the temperature on the surface opposite the fire reaches the melting point of glass fibres in the gypsum board; that is, approximately 700°C. Recommendations on thermal properties obtained independently by other researchers are presented. Overall, the advances improve temperature predictions and broaden the range of walls that can be modelled including staggered stud walls as well as ordinary cavity walls. Copyright © 2002 John Wiley & Sons, Ltd.     

Fire behavior of regular and latent heat storage gypsum boards

This paper investigates the fire behavior of a regular and an energy storage gypsum board with latent heat storage characteristics when exposed to fire temperatures. Gypsum board samples, with and without a microencapsulated paraffin mixture phase change material, are studied at material and board level. At the material level, measurements of the physical properties, that is, mass and effective thermal conductivity, as a function of temperature, as well as differential scanning calorimetry experiments, in inert and oxidized environments, are performed. At the board level, specimens are inserted into a preheated oven, and the temperature evolution at preselected board locations is recorded. Both experimental procedures reveal significant information concerning the evolution of the various thermochemical processes taking place inside the gypsum boards during their heating. Results indicated the different fire behavior of the samples at different temperature ranges. At temperatures up to 300°C, the materials act as a fire retardant because of the dehydration of the free and chemically bound water contained in the gypsum boards. On the other hand, at temperatures higher than 300°C, the temperature rise within the samples is enhanced and accelerated because of the oxidation of the phase change material and their external finishing. Copyright © 2014 John Wiley & Sons, Ltd.     

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.     

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 bolted connections in laminated veneer lumber

This paper describes an investigation into the fire performance of bolted tensile connections in laminated veneer lumber (LVL) made from radiata pine. The capacity of the bolted connections depends on the embedment strength of the wood and on the yield moment of the bolts. The purpose of the research was to develop a prediction method for the time to failure of the connections when exposed to fire. An experimental investigation was carried out on the axial tensile strength of three types of bolted connections that utilized either wood or steel splice plates. Some specimens were tested at ambient temperatures while similar specimens were tested in fire conditions with a constant applied load. In addition, single‐bolted connections were tested under constant elevated temperature conditions to determine the embedment strength of the LVL. Connections with no steel plates, or with steel plates slotted between the timber members, performed better than those with exposed steel. A simplified design approach is proposed, using an extension of the Johansen formulae, such that the embedment strength of the LVL depends on the temperature in the bolt. Copyright © 2009 John Wiley & Sons, Ltd.     

Full scale experiments for evaluating theoretical fire wall models

The aim of the research described in this paper was to provide experimental results for the evaluation of theoretical models for predicting the behaviour and time‐to‐failure of loadbearing and non‐loadbearing wood framed walls in fire. References for thermal and mechanical properties of wood and gypsum board are given to provide comprehensive input for the evaluation of theoretical wall models. The scope of the research involved full‐scale uninsulated cavity walls with well‐controlled clearly known conditions including initial ambient vertical load capacity for benchmarking the reduction in capacity and stiffness, rotational stiffness of supports, eccentricity of vertical load, elastic moduli of wood and gypsum board in compression, stiffness of slip between gypsum board and studs and end stud effects. The experiments were repeated and they demonstrated that the controls led to high consistency in the results despite the inherent large variability of the mechanical properties of wood. The results include temperature distributions, initial vertical load capacity, load‐deflection plots and times‐to‐failure. The results show that the temperatures in the studs are approximately uniform until all the moisture is vaporized. Thermal properties of wood will not vary significantly for consistent density, moisture content and species of wood. The main structural actions that should be modelled for different loading regimes are deduced. Copyright © 2004 John Wiley & Sons, Ltd.     

Fire-Resistant joints in gypsum wallboard

In situations where joint failure in the protective gypsum membrane is critical to the fire resistance of the system, wallboard manufacturers recommend application of two layers of wallboard with joints in the face layer staggered with joints in the backerboard. Unfortunately, the additional weight load that a second layer of wallboard imposes on the building assembly renders the technique impractical in some situations. Two examples are wallboard ceilings attached directly to wood joist or wood truss floor systems or suspended by hanger wire to steel furring channels below these floor systems. Small-scale laboratory tests demonstrated that the installation of steel ‘Tee’ strips in the finished joint between adjacent gypsum wallboard panels significantly increased the resistance of the joint to passage of fire and hot gases. Use of these strips in the construction of gypsum wallboard protected building systems should provide a significant increase in the fire resistance of the entire assembly without greatly increasing the weight load imposed upon the assembly.     

Sound‐transmission‐class and fire‐resistance ratings for wood‐frame floors

A collaborative government‐industry research programme was carried out at the National Research Council Canada to develop new sound‐transmission classes and fire‐resistance ratings for wood‐frame floor assemblies protected by gypsum‐board ceilings. Forintek Canada Corp., the Canadian Wood Council, and five manufacturers of wood I‐joists participated in the programme on behalf of the wood industry. Fire‐resistance ratings developed through the research programme range from 30 min to 1h: sound‐transmission classes range from 20 to 65. Many of the ratings will be published in the next edition of the National Building Code of Canada. This paper highlights some of those sound‐transmission class and fire‐resistance ratings and describes how they were derived from data obtained through the research programme. Copyright © 2000 John Wiley & Sons, Ltd.     

Surface parameters from small-scale experiments used for measuring HCl transport and decay in fire atmospheres

The decay of HCl was investigated in two small-scale scenarios: pure HCl injection into a 31 chamber and combustion of plasticized PVC in a 2001 chamber. The effects investigated included (1) humidity, (2) temperature, (3) concentration of HCl and (4) wall material. Surface materials studied were PMMA, ceiling tile (front and back), Marinite, painted PMMA, unpainted gypsum board and cement. In view of the very rapid HCl decay in most of those surfaces, the effects were often examined with small ‘chips’ of materials in a PMMA chamber, with fresh walls for each experiment. Experiments were also carried out to investigate the effect of surface ageing, with painted gypsum board, painted PMMA and unpainted gypsum board walls. HCl decay is very fast in cement or unpainted gypsum board surface (almost impossible to saturate with HCl) and almost as fast on ceiling tile and Marinite. Saturation of HCl can be reached on painted gypsum board and painted PMMA surfaces, albeit at different rates. An earlier empirical model from mathematical fitting had been followed by a new HCl generation, transport and decay model, with a sound physical basis. This allowed calculations of parameters for all the surfaces used. Much work has already been done in devising and writing a zone model for use together with fire hazard models (particularly the NIST model, FAST) to calculate correct HCL concentrations in various fire scenarios. This work, which concludes the investigation of these two static fire scenarios for the surfaces analysed, represents one more step in the pursuit of that goal.     

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.     

Experimental fire analysis of steel‐to‐timber connections using dowels and nails

The paper describes and discusses the results of an extensive testing programme on the structural behaviour of timber connections under ISO‐fire. The results of reference tests performed at normal temperature are also presented. From the variety of timber connections multiple shear steel‐to‐timber connections with dowels and slotted‐in steel plates and connections with steel side plates and annular ringed shank nails were experimentally studied. Particular attention was given to the analysis of the efficiency of different strategies in order to increase the fire resistance of the timber connections. The test results showed that unprotected multiple shear steel‐to‐timber connections with dowels designed for normal temperature reached a fire resistance of about 30 min. A reduction of the load level applied during the fire did not lead to a significant increase of the fire resistance. By increasing the side timber members as well as the end distance of the dowels by 40 mm the connections reached a fire resistance of more than 70 min. Connections protected by timber boards or gypsum plasterboards showed a fire resistance of around 60 min. Thus, from a fire design point of view these strategies were favourable in order to increase the fire resistance of the connections significantly. Unprotected connections with steel side plates and annular ringed shank nails failed already after about 12 min due to large deformations of the nails and the steel side plates directly exposed to fire. By protecting the steel side plates using an intumescent paint the fire resistance of the connections was increased to around 30 min. The test results enlarged the experimental background of timber connections in fire significantly. Copyright © 2009 John Wiley & Sons, Ltd.     

Charring of protected wood studs

The charring of wood studs has been studied in the cone calorimeter at constant heat flux 50 kW/m² and compared to data from full-scale furnace wall tests. The wood studs were unprotected or protected by gypsum plasterboards on the exposed side. Similar charring depths were found and the data analysed mainly in terms of fire exposure. A simple small-scale technique was developed to measure the heat transfer through protective boards and the charring depth of wood studs. These properties are essential for the load bearing capacity of wood frame structures. © 1998 John Wiley & Sons, Ltd.     

Simplified correlations of gypsum board thermal properties for simulation tools

The current work proposes for the first time an integrated set of simplified correlations for the thermal properties, i.e. effective thermal conductivity, effective specific heat and effective density, of commercial gypsum boards as a function of temperature that can be easily incorporated in dedicated computational tools in order to simulate the fire behavior of a gypsum board. The proposed correlations are based on experimental data purposely performed in the frame of this work, as well as on literature experimental data and theoretical approximations. The applicability and the accuracy of the correlations are established by simulating the fire behavior of various types of gypsum boards exposed to different fire conditions. For the validation of the developed correlations, an in‐house developed code is utilized, taking into account thermal properties produced by the proposed correlations. The predictions are compared with two published sets of experimental data, as well as with one experimental data set performed in the current work. The results indicate that the proposed correlations can be reliably utilized in computational tools in order to accurately predict the fire behavior of commercial gypsum boards. Copyright © 2014 John Wiley & Sons, Ltd.