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.     

Best practices for modeling structural boundary conditions due to a localized fire

Recent studies suggest the assumption of uniform heating that is used in current structural fire design cannot be assumed conservative, especially if the fire is expected to burn locally. Aside from design equations, which have limited applicability, a common approach to simulating structural members subjected to a localized fire is modeling the fire-structure interaction using a coupled computational fluid dynamics (CFD)-finite element (FE) model. In the existing literature, a wide range of methods and parameters are used when determining the boundary conditions at the fire-structure interface, specifically regarding the representation of net heat flux, heat transfer coefficient, and surface emissivity of steel. The purpose of this study is to investigate various methods for representing the boundary conditions in terms of accuracy and computational efficiency and then identify best practices. In conclusion, our study found that net heat flux predicted by adiabatic surface temperature, a nonconstant heat transfer coefficient, and a surface emissivity of 0.9 for steel was the most reliable thermal boundary condition in a coupled CFD-FE model of a localized fire. These recommendations are based on the two cases studied here, and caution should be used when applying these results to future studies.     

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.     

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.     

Evaluation of thermal fire hazard of 10 polymeric building materials and proposing a classification method based on cone calorimeter results

The use of polymeric building materials has been grown in many countries of Middle East in recent years. However, there are only a few fire testing laboratories in this region. Therefore, development of a method for controlling the reaction to fire of materials with bench scale tests is necessary. Providing a framework for classification of thermal fire hazard of materials based on bench scale heat release rate results was attempted. The fire behavior of 10 polymeric building materials was tested with cone calorimeter. The relationship between reaction to fire variables and physical properties of tested samples was examined. The thermal fire hazards of materials were assessed using methods presented by different researchers and with Conetools software. The results revealed that time to ignition, peak rate of heat release, and total heat release are essential variables for determining the fire hazard of materials. A classification method is proposed, which can be used in building codes in countries where the full‐scale test facilities are not available. The method also can be used for quality control purpose and evaluation of fire behavior of materials in bench scale by manufacturers. An example of potential requirements for interior finishes for some occupancy types is also presented. Copyright © 2013 John Wiley & Sons, Ltd.     

特殊消防设计在大型高铁车站设计中的运用

近年来在基础设施建设的投入显著增强,出现了较多的超高层建筑和大体量单体建筑,这就在建筑消防设计方面带来了许多问题。以在建的大同至张家口客运专线某站为例,探讨特殊消防设计在大型单体建筑中的运用,提出了一些特殊消防设计方案,进行了一系列消防安全性验证,证明了特殊消防设计能够解决大型单体建筑消防设计与现行规范的矛盾。     

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.     

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.     

Rectification of “restrained vs unrestrained”

For furnace testing of fire-resistant floor and roof assemblies in the United States, the ASTM E 119 standard (and similarly the UL 263 standard) permits two classifications for boundary conditions: “restrained” and “unrestrained.” When incorporating tested assemblies into an actual structural system, the designer, oftentimes a fire protection or structural engineer, must judge whether a “restrained” or “unrestrained” classification is appropriate for the application. It is critical that this assumption be carefully considered and understood, as many qualified listings permit a lesser thickness of applied fire protection for steel structures (or less concrete cover for concrete structures) to achieve a certain fire resistance rating if a “restrained” classification is confirmed, as compared with an “unrestrained” classification. The emerging standardization of structural fire engineering practice in the United States will disrupt century-long norms in the manner to which structural behavior in fire is addressed. For instance, the current edition of the ASCE/SEI 7 standard will greatly impact how designers consider restraint. Accordingly, this paper serves as an exposé of the “restrained vs unrestrained” paradigm in terms of its paradoxical nature and its controversial impact on the industry. More importantly, potential solutions toward industry rectification are provided for the first time in a contemporary study of this paradigm.     

Small-scale assessment method for the fire resistance of historic plaster system and timber structures

The primary protection against the charring of timber is ensured by protection materials. Today, there are only a limited number of materials given in design codes as fire protection materials for timber. Historic surface finish materials such as plasters have rarely been studied with respect to fire; no design values exist in the current fire part of Eurocode 5. Full-scale fire testing is costly to assess the fire performance of material combinations, thus this study presents a useful tool that is specifically tailored to evaluate the fire protection ability of materials in small-scale. A review of conducted tests demonstrate that the cone heater of a cone calorimeter is a dependable device to estimate the charring performance of protected timber specimens as the test results approximate the ones obtained from furnace tests. This work contributes to the assessment of fire resistance performance of various combinations and types of plaster systems found in existing timber buildings that often require an individual approach for an adequate fire risk analysis and design decisions to meet current fire safety regulations with respect to the load-bearing capacity and compartmentation of building structures. Increased knowledge on the fire protection performance of traditional plasters is believed to facilitate their wider use in timber buildings, primarily to preserve their significance as part of the cultural built heritage.     

成品库防火性能化设计火灾探测器选择研究

介绍国内火灾自动报警设计规范的各种探测器选择方法,根据防火性能化分析原理,针对某成品库大空间建筑屋面取消喷淋的设计方案,为保证火灾自动报警探测及时可靠,确保建筑的耐火极限时间,采用美国Fire Dynamic Simulation软件,通过火灾热动力过程和探测器启动的有限元数值模拟,对成品库大空间建筑的火灾及探测进行性能化分析;通过优化设计采用线型红外光束感烟火灾探测器设计,使火灾探测报警系统既安全可靠又经济合理。     

Ansätze zur numerischen Berechnung von Brandeinwirkungen auf Bauteile

Within the context of the preparation of fire safety certificates for industrial buildings methods of fire protection engineering are frequently used. Computational fluid dynamics represents instruments for these methods and is used for modeling and calculation of fire scenarios. In this paper a method of fire technological measurement, which is based on computational fluid dynamics and structural mechanics, was used for an industrial building. Unsteady temperature profiles were used as an input value for the building component calculation. The outcomes were finally used for the calculation of the equivalent length of fire, which is an important term to reckon the fire resistance rating of building components.     

Design car fire size based on fire statistics and experimental data

Passenger vehicle fires present a significant fire hazard in enclosed car parks. Accordingly, this hazard is often used as a design fire scenario for the application of fire protection systems. Specific fire protection standards, like NFPA 88A:2019 and NFPA 502:2020 in the United States (US) or BS 7346-7:2013, NBN 21-208-2:2014, VDI 6019-1:2006, NEN 6098:2010 and ITB 493:2015 in Europe, provide varying requirements for car park fire protection. Car parks fire strategies, especially when smoke control systems are used, often make use of performance-based methods, in which fire growth (ie, heat release rate [HRR]) plays a fundamental role. The chosen HRR can influence the specification of car park construction and on smoke control system calculations. This article presents a review of 44 full-scale car fire tests together with Polish and British passenger car fire statistics from the last 8 years. Based on the collected data and the averaged tests, HRR values provided in this article could assist local authorities and stakeholders determine optimal fire safety design criteria for car parks.     

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.     

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.     

Estimation of the temperature profiles of reinforced concrete cross sections exposed to standard fires by using artificial neural networks with different topologies

The thermal analysis in structural members can be extremely complex, especially for materials that retain moisture and have a low thermal conductivity. The simplest method of defining the temperature profile through the cross section is to use test data presented in tables or charts, which are published in codes or design guides. These tabulated data are generally based on standard fire conditions. Annex A of TS‐EN1992‐1‐2 provides a series of calculated temperature profiles for concrete slabs or walls, beams, and columns. But these profiles are given for specific cross‐section dimensions and standard fire resistance durations. The main purpose of this study is to estimate the temperature profiles of reinforced concrete beam and column cross sections by using artificial neural networks (ANN) with different topologies. When modeling ANN, it is benefited from multi‐layer ANN, which uses supervised learning rule. During training and testing stage of ANN, the results obtained from the aforementioned temperature profiles are used. The temperatures values were read from the temperature profile charts according to standard fire durations, cross‐sections height and widths, and x and y coordinates of the points by the reference point. By testing ANN with different topologies in conclusions, its usability, advantages, and disadvantages are evaluated. Copyright © 2015 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.     

Experimental study on insulative properties of intumescent coating exposed to standard and nonstandard furnace curves

This paper reports the results of an experimental study on two types of intumescent coating exposed to the ISO834 standard fire and three nonstandard fire curves. The nonstandard fires were all less severe than the standard fire. A total of 72 intumescent coating protected steel specimens were tested. The expanded thickness of intumescent char was measured, and the pore feature was observed. Constant thermal conductivity for each specimen was calculated based on the measured steel plate temperature. Thermogravimetric analysis (TGA) test was carried out, and the results show that more gas is trapped within the coating due to better matching of thermal behaviour between gas evolution and polymer viscosity as the rate of heating increases. The constant effective thermal conductivities for the intumescent coating under the nonstandard fires were 65% (type‐W) and 35% (type‐S) higher than that under the standard fire, which resulted in an overestimation of the coating failure time up to 15 and 11 minutes, respectively. Therefore, it is sometimes insecure to use results from standard fire tests guiding the design of coating thickness for steel elements under nonstandard fire conditions.     

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.