A review of methods for determining structural fire severity—Part I: A historical perspective

There is a risk of a building suffering unsustainable structural damage in the event of a large fire. Therefore, it is necessary to design buildings to withstand expected fires. A widely used simplified calculation method is the so-called ‘time-equivalence’ method. There are significant concerns about the suitability of this method. This paper is Part I of a twofold study examining the state of the art of time-equivalence methods. The purpose of this paper is to provide a detailed background of the development of time-equivalence methods since its first introduction in 1928 and to provide an initial high-level assessment of the accuracy of these methods. A simple scoring system is used to assess the methods based on the accuracy of the analysis techniques used in their derivation. The study revealed that most methods do not account well for structural system response to fire exposure. While some time-equivalence methods do yield accurate results, further analysis is required to fully assess their suitability.     

An extended travelling fire method framework for performance-based structural design

This paper presents the extended travelling fire method (ETFM) framework, which considers both energy and mass conservation for the fire design of large compartments. To identify its capabilities and limitations, the framework is demonstrated in representing the travelling fire scenario in the Veselí Travelling Fire Test. The comparison between the framework and the test is achieved through performing a numerical investigation of the thermal response of the structural elements. The framework provides good characterization of maximum steel temperatures and the relative timing of thermal response curves along the travelling fire trajectory, though it does not currently address a non-uniform fire spread rate. The test conditions are then generalized for parametric studies, which are used to quantify the impact of other design parameters, including member emissivity, convective heat transfer coefficient, total/radiative heat loss fractions, fire spread rate, fire load density, and various compartment opening dimension parameters. Within the constraints of this study, the inverse opening factor and total heat loss prove to be the most critical parameters for structural fire design.     

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.     

Development of a numerical approach based on coupled CFD/FEM analysis for virtual fire resistance tests—Part A: Thermal analysis of the gas phase combustion and different test specimens

In the present two‐parted study, a numerical approach is shown to consider fire resistance tests in virtual space, including the combustion, thermal analysis of the test specimen, and the deformation process. This part is dealing with the combustion process and thermal analysis of different building materials tested in a fire resistance furnace. Instead of using coupled computational fluid dynamics (CFD)/finite element method simulation for the combustion and thermal heat conduction in the solid, which is commonly used in literature, the present approach considers these transport phenomena in one CFD simulation. This method enables a two‐way coupling between the gas phase and the solid material, where chemical reactions and the release of volatile components into the gas phase can occur (eg, release of water vapour from gypsum). To validate the numerical model, a fire resistance test of a steel door, which is a multilayer construction, and a wall made of gypsum blocks were experimentally and numerically investigated. Due to the chemical reactions inside the gypsum, water vapour is released to the gas phase reducing the flue gas temperature about 80 K. This effect was taken into account using a two‐way coupling in the CFD model, which predicted temperatures in close accordance to the measurement.     

Comparing simple and advanced tools for structural fire safety engineering

The present paper gives an overview of the actual tools available for the estimation of the fire development and of the resulting thermal actions on structural members. A case study is developed on the basis of the Fire Safety Engineering methodology, respectively with two different approaches, one based on ‘advanced’ tools and another one based on ‘simplified’ tools. Indeed, three categories of fire models are used in this study, each of which corresponding to a different level of precision and complexity: hand calculations, zone models, and computational fluid dynamics (CFD) models. The case study is relative to the calculation of the heating of a portal frame in a gymnasium, under localised real fire conditions. It is shown through comparisons that, in this case, predictions of analytical methods are, to certain extent, in good agreement with predictions of the CFD model. In particular, it is demonstrated the relevance of using a simplified method of EN 1991‐1‐2 to predict thermal actions to vertical members. The obtained results also highlight the need to develop more relevant analytical methods in order to predict the temperature field during a fire in a large volume. Copyright © 2014 John Wiley & Sons, Ltd.     

Performance of a light timber‐framed compartment in natural fire subjected to lateral load

A common approach for designing buildings for lateral stability during and post‐fire in New Zealand is to ensure that a fire‐rated structure does not collapse when subjected to a nominal horizontal force. For external walls of residential buildings, which are required to resist a lateral load of 0.5 kPa, it is hypothesised that the adjacent unrated construction could provide sufficient support. A natural fire experiment has been conducted to evaluate the fire performance of a laterally loaded light timber‐framed compartment, with external dimensions of 4.33 m × 3.35 m and a stud height of 2.4 m constructed with a timber truss roof and plasterboard ceiling. During the experiment, the ceiling collapsed at 12 to 13 minutes, and the bottom chord of the roof truss failed in tension after 28 minutes which resulted in the fire‐rated wall losing its lateral stability at 28 minutes. The fire severity experienced in the compartment has been estimated to correspond to an equivalent time of 33‐minute exposure to a standard furnace time‐temperature. It is concluded that there is no need to provide nominal (additional) moment‐resisting fixity at the base of the fire‐rated wall when exposed to the standard fire for no more than 30 minutes.     

Evaluating the heat resistance of thermal insulated sandwich composites subjected to a turbulent fire

The fire structural response of sandwich composite laminates incorporating bio‐derived constituents subjected to a turbulent flaming fire was investigated. Fire structural tests were conducted on thermal insulated sandwich composites incorporating a thin surface‐bonded non‐woven glass fibre tissue impregnated with char‐forming fire retardant, ammonium polyphosphate. The sandwich composite laminates were loaded in compression at 10%, 15% or 20% of the ultimate compressive strength while simultaneously subjected to turbulent flames imposing an incident heat flux of 35 kW/m². Generally, the failure time increased with the reduced applied compressive load. The thermal insulated sandwich composite laminates had considerably improved fire resistance in comparison to their unmodified counterparts. The unmodified composites failed 96 s earlier than the thermal insulated specimens when the compression load was 10% of the ultimate compressive strength. The presence of ammonium polyphosphate at the heat‐exposed surface promoted the formation of a consolidated char layer, which slowed down heat conduction into composite laminate substrate. The fire reaction parameters measured via the cone calorimeter provided insights into the thermal response hence fire structural survivability of sandwich composite laminates. Copyright © 2015 John Wiley & Sons, Ltd.     

Analysis of the behaviour of the structural concrete after the fire at the Windsor Building in Madrid

The analysis of the concrete subjected to high temperatures is usually undertaken by means of tests specifically designed and carried out in the laboratory, or by using theoretical approaches using standardized curves for theoretical fires. An analysis by different techniques has been carried out on structural concrete to real fire of Windsor Building in Madrid, which was severally damaged by a fire in 2005. These techniques are X‐ray diffraction, differential thermal and thermogravimetric analysis and backscattered electron microscopy with dispersive X‐ray microanalysis. Samples of the concrete were taken from different floors in the building and analyses were carried out at different depths starting from the surface exposed to the fire itself. The analysis allows the damaged area to be limited as well as situating the 500^°C isotherm in the concrete element. In accordance with the results obtained, the damage is limited to just a few centimeters from the surface exposed to the fire itself, in spite of its prolonged exposure to the fire. This would justify that the concrete has demonstrated a suitable resistant behaviour. Likewise, it can be deduced from the results obtained that the fire, to which the concrete was subjected, can be qualified as severe. Also, these results can confirm that the calculation hypothesis in the project is correct in relation to the fire resistance exigencies of the concrete. Copyright © 2009 John Wiley & Sons, Ltd.     

Effect of increased charring on the narrow side of rectangular timber cross‐sections exposed to fire on three or four sides

Owing to the influence of two‐dimensional heat transfer, fire tests and heat transfer calculations show that charring on the narrow side of rectangular timber cross‐sections may be considerably greater than charring on the wide side. For timber members unprotected throughout the time of fire exposure as well as members initially protected from fire exposure, it is shown by calculation, that the relationship between charring on the narrow side and time is nonlinear. In order to take into account increased charring on the narrow side of timber members a section factor k_s was determined. By calculation it is shown that bending moment resistance is only insignificantly influenced by the effect of two‐dimensional heat transfer and the factor k_s can therefore be neglected, making the fire design of timber members easier. Copyright © 2011 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.     

Inorganic polymeric materials for passive fire protection of underground constructions

Protection against fire for reinforced concrete constructions is of great importance worldwide. There is a general perception that concrete structures are incombustible and thus, they have good fire‐resistance properties. In a real fire incident, however, concrete can be subjected to excess temperatures causing severe spalling and serious damage to concrete structures with significant economic cost and high potential risk to human life safety. Although a variety of fire‐protection methods exist, there is always a need for the development of new materials with improved thermophysical properties and low cost. Inorganic polymeric materials are promising from this point of view. They are incombustible, combining excellent physical, chemical, mechanical and thermal properties with low production cost and significant environmental benefits. In this work, the thermophysical properties of ferronickel slag‐based inorganic polymeric materials are studied. The results from the laboratory scale experiments are promising and indicative of the large‐scale behavior of material. The effectiveness of this material has to be proved in large‐scale experiments at higher temperatures simulating several severe fire scenarios as well as under all kinds of mechanical loading before concluding for its applicability as a fire protection system. Copyright © 2012 John Wiley & Sons, Ltd.     

A structural optimization approach in process synthesis—II : Heat recovery networks

Several formulations of the transshipment model from Operations Research are proposed for the optimal synthesis of heat exchanger networks. The linear programming versions are used for predicting the minimum utility cost, and can handle restricted matches and multiple utilities. The mixed-integer programming version yields minimum utility cost networks in which the number of units is minimized, while allowing stream splitting and selection of most preferred matches. It is shown that the transshipment models can also be incorporated easily within a mixed-integer programming approach for synthesizing chemical processing systems. Several numerical examples are presented which show that the proposed models are computationally very efficient.     

An experimental study of fire development in deep enclosures and a new HRR–time–position model for a deep enclosure based on ventilation factor

The behaviour of fire within a deep (high‐depth‐to‐height ratio) enclosure with various openings at one end has been studied experimentally. Sixteen fuel trays were placed within an 8.0m long × 2.0m wide × 0.6m high steel enclosure. The experiments confirmed previous smaller‐scale experiments, which showed that the fires in deep enclosures are strongly influenced by the ventilation and are not at all uniform throughout the depth of the enclosure. The severity of exposure of structural members is much more severe close to the ceiling near the front of the enclosure compared with the back of the enclosure. Based on the test data that can be found in this report, as well as other well‐known tests, a heat release rate–time–position model is proposed for fire development in deep enclosures. The same sets of test data are also used to evaluate other model predictions. Finally, a recommendation is made to choose a model based on the shape of the enclosure (i.e. deep, wide, square, etc.). Copyright © 2008 John Wiley & Sons, Ltd.     

Overall stability analysis of oversized steel‐framed buildings in a fire

Our present paper summarizes the shortcomings in the current fire‐resistant design of oversized steel structures and proposes a method for overall stability analysis of steel structures in the event of fire. The Fire Dynamics Simulator (FDS) software platform–based large‐eddy simulation technology can accurately reflect the environment in a fire scenario and correctly predict the spatial–temporal change in the smoke temperature field within an oversized space. Adopting the FDS software and finite element structural analysis (ANSYS) coupling can fundamentally overcome the natural defect of adopting the International Organization for Standardization (ISO) standard curve (or other indoor homogeneous temperature increase curves) that substitutes a point for the overview of a field. They reflect the structural additional internal force and internal force redistribution incurred by the gradient temperature difference of the spatial–temporal changing nonhomogeneous temperature field and both theoretically and technically realize the analysis of structural heat transfer and mechanical properties in a natural fire. Furthermore, a modified model to predict the steel temperature curve in localized fire is also proposed. The localized fire in large spaces can be treated as a point fire source to evaluate the flame thermal radiation to steel members in the modified model. Copyright © 2014 John Wiley & Sons, Ltd.     

Simulation of Coyote series trials—Part II: A computational approach to ignition and combustion of flammable vapor clouds

Accidental releases of flammable gases may lead to major fires with extensive effects on the surroundings, mainly due to the intense thermal load emissions. In this paper, a computational approach based on fluid dynamics techniques was attempted aiming at the estimation of resulting thermal radiation emissions and overpressure in large scale cloud fires. In particular, the work dealt with the simulation of Coyote series trials, which conducted in 1981 by Lawrence Livermore National Laboratory (LLNL) and involved the release, dispersion, ignition and combustion of unconfined natural gas clouds in the open-air. In the computations, the CFD code CFX 5.7 was utilized which, in addition to the standard three-dimensional Navier-Stokes equations, incorporates the k-ε model for turbulence modeling, the Eddy Dissipation model for combustion and P1 model for radiation transport modeling. Computational thermal radiation histories were compared with experimental data from totally four trials showing a reasonably good agreement for several locations in the field. Discrepancies were laid on overestimation of the thermal load receipted at a certain location, nevertheless within a factor-of-two of the observed values. Moreover, positive peak overpressures were sufficiently low to indicate that the combustion of the cloud yielded a flash fire rather than an explosion.     

Assessment of fire behaviour of high‐speed trains' interior materials: small‐scale and full‐scale fire tests

The development of fire‐safety measures for high‐speed passenger trains has been focused on preventing fire initiation or delaying fire growth and spread through small‐scale tests of the materials used in trains. However, new fire‐safety approaches for trains consider a systemic approach. This approach considers numerous global factors that influence fire dynamics, such as the influence of vehicle design, selection of materials, and active and passive protection systems installed. In the present paper, the results of small‐scale and full‐scale tests carried out on the new generation of high‐speed trains operating in Spain are presented. This rolling stock is classified as category B according to the Technical Specification for Interoperability and Operation Category 3 according to EN 45545–1. The results confirmed good fire behaviour using both approaches (small and full‐scale tests). Additionally, several analyses have been performed, including an analysis of the quality of materials used for making different components of the passenger compartment and the influence of ignition source position on fire development. Copyright © 2013 John Wiley & Sons, Ltd.     

Thermal and mechanical transient behaviour of steel doors installed in non‐load‐bearing partition wall assemblies during exposure to the standard fire test

In this paper, the authors present experimental results and observations of four full‐scale standard fire tests on single‐leaf steel doors and steel frames installed in 3 × 3 m non‐load‐bearing partition walls. Three full‐scale fire tests were performed on steel doors installed in lightweight partition walls constructed by using steel C‐section studs with gypsum boards fixed on both sides. Two lightweight walls incorporated Rockwool cavity insulation, while the third lightweight wall was constructed without cavity insulation. The fourth fire test involved a steel door installed in a masonry partition wall. While the steel door leaf and door frames were identical in all four full‐scale tests, only the steel door installed in the masonry wall achieved the desired fire resistance rating of 30 min. The integrity criterion for fire resistance was determined for the scenario when the door opened away from the furnace. The duration of fire resistance according to the integrity criterion was found to be 38, 25 and 19 min for the same door when installed in masonry wall, uninsulated lightweight wall and insulated lightweight wall respectively. For the thermal insulation criterion of fire resistance, the scenario of the door opening into the fire was found to be the most onerous. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.     

A review of fire growth and fully developed fires in railcars

A literature review was performed to assess the state of knowledge of the effects of railcar interior finish materials on fire growth and fully developed fires from railcars. An overview is provided on standards and requirements currently used to regulate interior finish materials. Following this review, an overview of experimental and computational research is provided on railcar interior finish flammability and its impact on fire growth. A survey of the research on fully developed fires and the potential heat release rates of railcars is then presented. This includes scaling laws, experimental research, and model development. Future research recommendations are then presented.