Natural Fire Tests Research Articles

Full-scale natural fire tests on gypsum lined structural insulated panel (SIP) and engineered floor joist assemblies

SIPS are formed from the lamination of two oriented strand board (OSB) facing plates and a highly insulating polymer-based foam such as expanded polystyrene (EPS) or polyurethane (PUR). The resulting lightweight panels are typically used as primary load-bearing compression elements for buildings such as domestic dwellings, apartment blocks, schools and hotels. The regulatory fire performance of SIPS, like many systems, is assessed via a standard fire test. However, it is widely accepted that this is merely a comparative method for determining the relative performance of one product when compared to another; hence, it gives little indication of a component's likely behaviour in a real fire. With this in mind BRE Global, with support from the UK Department for Communities and Local Government (CLG), have undertaken a research programme to determine the performance of SIPS subject to realistic fire conditions. The research programme exposed four two storey SIP buildings to natural fire scenarios using timber cribs. Two buildings were constructed with EPS core SIPS. The other two were constructed with PUR core SIPS. Each material set was subdivided by passive fire protection specification (PFP). These were specified on the basis of 30 and 60-min fire resistance. The experiments highlighted a number of weaknesses in the system performance of SIP structures with engineered floors. Firstly, where PFP is under specified or poorly installed, collapses of the engineered floor plate are very likely. Mechanisms for fire spread were also identified where fitting details were not appropriately sealed. In addition, there appeared to be little appreciable difference in the behaviour of buildings formed with EPS or PUR core SIPS. Finally, a number of system redundancies and alternative load paths were identified, which prevented total collapse of any of the test buildings.

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

SUMMARYGypsum 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.

Large scale natural fire tests on protected engineered timber floor systems

As part of an ongoing research project to investigate the performance in fire of specific types of innovative construction products and techniques (ICPT), BRE Global have carried out large-scale fire tests to determine the response of different floor systems to a realistic fire scenario. The principal objective was to determine the mode of failure of different floor systems to provide information to key stakeholders (particularly the Fire and Rescue Service), which can be taken into account in the dynamic risk assessments that underpin fire fighting operations. This paper presents the results and observations from those fire tests for three floor systems: (i) solid timber floor joists, (ii) I-section floor beams with solid timber top and bottom flanges and an oriented strand board (OSB) web, and (iii) a timber truss incorporating solid timber upper and lower chord members and a pressed steel web member. These reflect the two most common types of engineered floor systems used in the UK and allow for direct comparison with a more “traditional” form of construction.

Fire tests to study heat insulation scenario of galvanized rolling shutters sprayed with intumescent coatings

The purpose of this study, through standard furnace fire tests and a natural fire test, is to analyze the heat insulation behavior of galvanized rolling shutters sprayed with intumescent coatings. The following experiments and associated estimations demonstrated that in the 1-h standard fire-resisting tests, the radiant heat flux at a measuring point horizontally 1 m away from the center of an unexposed surface the radiation could reach 4.64 W/cm 2 for the traditional uninsulated galvanized rolling shutter, and that the radiant heat flux would be substantially decreased to 0.22 W/cm 2 for one with intumescent coating of 0.3 mm target thickness, which, during the heating process, expanded about 100 times in volume and then generated a certain insulation effect. Therefore the intumescent coatings on galvanized rolling shutters have been proved by this study to be a feasible method of insulation, which can be applied in the future fire compartment design of buildings.

A parametric natural fire model for the structural fire design of multi-storey buildings

A parametric natural fire model is presented, which is derived on the basis of simulations with heat balance models for realistic natural design fires, taking into account the boundary conditions of typical compartments in residential and office buildings. These so-called iBMB parametric fire curves are formulated with the help of simplified empirical equations which can easily be used for structural fire design as part of a performance-based natural fire design concept. The iBMB parametric fire curves are checked and validated by comparison with results of different heat balance models and with published fire tests from different fire research laboratories. In addition, a natural fire test in a test room with ordinary office room furnishings has been performed which supports the parametric natural fire model presented here. The application of the iBMB parametric fire curves is demonstrated by means of an example.

Examples of fire engineering design for steel members, using a standard curve versus a new parametric curve

AbstractThis paper presents examples of the differences that can occur when a standard time‐temperature curve and a parametric time‐temperature curve are used to determine temperatures likely to be reached by uninsulated and insulated steel members during a fire. For low and moderate structural fire severity situations, determination of the adequacy of a steel member by comparing the temperature reached in a ‘design fire’ with the limiting temperature based on the member heat sink characteristics, extent of insulation and utilization factor is becoming increasingly common fire engineering design practice. For this it is important to have an accurate and widely applicable parametric fire model as is practicable.The standard time‐temperature curve used in the examples is the ISO 834 curve. The two parametric time‐temperature curves used in the paper are the Eurocode parametric curve and a recently developed one termed the ‘BFD curve’. The latter has been found to fit the results of a wide range of actual fire tests more closely than do existing parametric curves and is mathematically simpler in form.The shape of the BFD curve and the parameters used to define it bear a strong relationship to both the pyrolysis coefficient (R/Avhv0.5) and the opening factor, F02. The curve also models the development of fire without the need for time shifts. It uses a single and relatively simple equation to generate the temperature of both the growth and decay phases of a fire in a building and only three factors are required to derive the curve. These factors are (i) the maximum gas temperature, (ii) the time at which this maximum temperature occurs, and (iii) a shape constant for the curve. If desired, the shape constant can be different on the growth and the decay sides to model a very wide range of natural fire conditions and test results.This paper presents an overview of the background to the BFD curve. It then illustrates its use in a simple fire engineering design application, where the adequacy of a steel beam is checked using the Eurocode parametric curve and the BFD curve to represent the fire. Copyright © 2004 John Wiley & Sons, Ltd.

Effective stiffness modelling of composite concrete slabs in fire

In this paper a modified layered slab element is developed based on the layered procedure previously developed for the modelling of composite slabs in fire. In the development reported here, the ribs forming the lower part of any slab cast onto metal decking are included in the slab modelling. The basic idea is to use the nominal thickness of the composite slab as the thickness of the slab element, and to use an effective-stiffness factor to modify the material stiffness matrices of plain concrete in order to take into account the orthotropic properties of the slab. A maximum-strain failure criterion is used in the modelling of concrete. Three standard fire tests on metal-deck composite slabs and one full-scale natural fire test on the Cardington composite building frame are modelled for validation. The validations indicate that the model proposed is clearly capable of predicting the fire resistance of this type of composite slab in fire with reasonable accuracy. It is evident from this study that the influence of the ribs across the bottom of the slabs is significant and should be accounted for. The calculation of effective stiffness factors, which are based on the theory of elastic beam bending, is adequate and efficient, and the maximum-strain failure criterion is simple and suitable for such problems.