Standard Fire Exposure Research Articles

A Review of Models for the Charring Rate of Solid Wood, Nail- and Glue- Laminated Structural Members

Simple calculation models for charring rate of solid wood, nail- and glue-laminated structural elements for use in fire design of wooden structures have been compared with test results from the literature. The applicability to these structural elements, and the accuracy of the models, have been evaluated based on parameters influencing the charring rate, which include species, density, moisture content, char contraction factor, external heat flux, oxygen concentration and duration of the fire. The models evaluated in this article are applicable to one- or two-dimensional charring under standard fire exposure.

Test method for concrete spalling using small electric furnace

AbstractConcrete spalling can cause severe damage to concrete structure when exposed to fire. The spalling mechanisms are not very well understood. For the testing of spalling, full‐scale structural members should be used, as spalling tests are sensitive to size effects. Full‐scale testing in large furnace is costly and is not suitable for testing large number of concrete mixture trials. The standard and hydrocarbon fire time–temperature curves have rapid temperature rise during the initial phase. This temperature rise requires a gas furnace with high heating capacity and cannot be generated by electric muffle furnace commonly available in many laboratories.This paper presents a method to carry out spalling test in small‐scale specimens with exposure to rapid temperature rise using a commonly available electric furnace in the laboratories. The tests are based on 150 mm diameter cylinders that are laterally confined to simulate full‐scale structural members. The cylinder surface is exposed to rapid temperature rise by exposing through vertical and/or horizontal holes in pre‐heated small electric furnace. Some unconfined 100 mm diameter cylinders were also exposed horizontally to test the performance of confinement. The paper shows that the hydrocarbon fire and standard fire exposure can be simulated by manipulating the exposure location of the surface of the concrete cylinder. Ordinary Portland cement concrete cylinders with different strengths were tested and different spalling patterns were observed. The spalling patterns matched the test results from a gas furnace fire test simulating the fire curves. The tests demonstrated that the method is an effective and convenient technique to predict the spalling risk of a concrete. Copyright © 2009 John Wiley & Sons, Ltd.

An Approach for Evaluating the Fire Resistance of CFHSS Columns under Design Fire Scenarios

The use of concrete filling offers a practical alternative for achieving the required fire resistance in steel hollow structural section columns. However, the current prescriptive-based approach which evaluates fire resistance based on standard fire exposure does not account for realistic fire scenarios in the design of concrete-filled hollow structural section (CFHSS) columns. This article presents a methodology for evaluating the fire resistance of CFHSS columns under design fire scenarios without the need for costly computational models. The proposed approach is a derivative of the equal area concept, and evaluates the equivalent fire resistance of the column by comparing the time temperature curve of the standard fire exposure with that of the design fire exposure. The method has been validated against the results generated from finite element analysis (coupled heat transfer and strength analysis) on numerous CFHSS columns under a large number of design fires. The applicability of the approach in desi...

Fire Resistance of Steel C-Joist Floor Assemblies

This paper discusses the factors that affect the fire resistance performance of lightweight steel-framed (LSF) unrestrained floor assemblies protected with Type X gypsum board ceiling finishes. Sixteen fire resistance experiments were conducted on full-scale load-bearing steel C-joist floor assemblies using the ULC standard fire exposure time–temperature curve that is similar to ASTM E119 standard. Parameters investigated in this study include the effects of insulation installation, insulation type, joist spacing, resilient channel installation, resilient channel spacing, type of sub-floor layer and number of sub-floor layers versus number of gypsum board layers. The impact of these parameters on the fire resistance of steel C-joist frame floor assemblies is discussed. The fire resistance of LSF floors appears to be essentially governed by the number of gypsum board layers, spacing of the joists or resilient channels where the gypsum boards are attached, sub-floor type and insulation type. Other parameters are of secondary importance.

Temperature distribution within glued laminated timber during a standard fire exposure test

The purpose of this study was to investigate the temperature distribution within glued laminated timbers (glulams) made from five softwood species as determined by a standard fire exposure test (CNS12514). The results reveal that the temperature within the middle section of tested glulam increased with increasing fire exposure time. After a fire exposure of 30 min and 45 min, the average temperature in the center of middle section for tested glulams (with a cross-section of 266 mm in depth × 190 mm in width) ranged from 27.5–28.3 °C to 29.5–33.2 °C; whereas, the average temperature for tested glulams (with a cross-section of 266 mm in depth × 140 mm in width) increased rapidly (from 32.3–51.1 °C to 39.1–89.3 °C) with an increasing exposure time and a decreasing cross-section. It was also found that the temperature in the center of the middle section increased slower than that in the right side or left side of a glulam middle section. The temperature within glulams (78 mm from the surface) remained constant without significant influence of fire exposure time according to CNS 12514. It can also be observed that equations developed by the Swiss Federal Institute of Technology give a closer calculation for the temperature development in tested glulams with heat flux from three sides.

The charring depth and charring rate of glued laminated timber after a standard fire exposure test

The purpose of this study was to investigate the charring depth, charring rate and heat release rate of glued laminated timbers (glulams) made from five softwood species as determined by a standard fire test (CNS12514) and the cone calorimeter method. The results indicated that the average charring depth and charring rate of the bottom sides of specimens were higher than those of the lateral sides in the same specimen and after the same fire exposure conditions. The charring rates of most tested glulam specimens could meet the Eurocode 5 and Australian standard 1720.4. The charring rate in all glulam specimens showed a decreasing order as follows: Taiwania>Japanese cedar>China fir>Douglas fir>Southern pine glulam. Generally, the charring rate of glulam specimens decreases with an increase of density. The correlation coefficient ( r=0.53) for the relationship between the charring rate and density value was not high. However, a high correlation ( r=0.88–0.89) between the charring rate/density and density was found in further analysis. The average heat release rate and the total heat release of tested specimens were (in decreasing order): Taiwania>Japanese cedar>China fir.

Fire Resistance of Wood Joist Floor Assemblies

This paper discusses the factors that affect the fire resistance performance of lightweight wood frame unrestrained floor assemblies protected with Type X gypsum board ceiling finishes. Twenty-two fire resistance experiments were conducted on full-scale load-bearing wood joist floor assemblies using the ULC standard fire exposure time–temperature curve that is similar to ASTM E119 standard. Parameters investigated in this study include the effects of gypsum board screws spacing from board edges, insulation installation, insulation type, joist spacing for assemblies with gypsum board attached to resilient channels, joist depth, resilient channel installation, resilient channel spacing, sub-floor topping, number of sub-floor layers, and load magnitude. The impact of these parameters on the fire resistance of wood joist frame floor assemblies is discussed. The fire resistance of wood frame floors appears essentially to be governed by the gypsum board screw spacing from the board edges and the type of insulation in assemblies with one layer of gypsum board and by the resilient channel spacing and the gypsum board screw spacing from the board edges in assemblies with two layers of gypsum board. The effects of other parameters in assemblies with two layers of gypsum board such as the joist spacing where the gypsum boards are attached to resilient channels, installation of resilient channels, insulation installation, insulation type, adding gyp-crete topping above the sub-floor and number of sub-floor layers on fire resistance are relatively insignificant.

FIRE RESISTANCE OF WOODEN FLOOR-BEAM ASSEMBLIES OF JAPANESE TRADITIONAL POST AND BEAM CONSTRUCTION

Fire resistance tests have been conducted to develop wooden floor-beam assemblies of 45 minutes fire resistance for design loading conditions based on Japanese traditional post and beam construction. The tests were initiated with a 2m x 3m floor specimen consisting of six 1m x 1m small specimens of different specifications including four designs with beams exposed to the lower floor and two designs with ceiling panel beneath the beam to verify the integrity and thermal penetration through the floor panels. Beams to bear with the standard loading for domestic use and assemblies for 45 minutes standard fire exposure were then designed with the vertical deflection as the temporary index for compliance with the fire resistance standard. Large scale loaded fire tests were conducted on two designs, one with bare beam and another with ceiling panel, resulting in the achievement of 45 minutes prevention of flame and thermal penetration or buckling.

Response to Fire Exposure of the Pentagon Structural Elements

An overview of fire damage sustained by the Pentagon structural elements in the September 11, 2001, terrorist attack is provided. The fire intensity in some compartments of the affected areas inside the Pentagon was approximated to be between those of the two standard fire exposures ASTM E119 and E1529, based on the observed fire damage and estimated fuel load. Thermal analyses of the structural columns and beams were performed using the standard fire exposures to demonstrate the increased vulnerability of these structural elements once the concrete cover was lost.

Effective thermal actions and thermal properties of timber members in natural fires

AbstractFor the thermal analysis of structural or non‐structural timber members, using conventional simplified heat transfer models, thermal conductivity values of timber are normally calibrated to test results such that they implicitly take into account influences such as mass transport that are not included in the model. Various researchers and designers have used such effective thermal conductivity values, originally determined for standard fire exposure, to evaluate other fire scenarios such as natural fires. This paper discusses in qualitative terms some parameters that govern the burning of wood and their influence on effective conductivity values. Reviewing fire tests of timber slabs under natural fire conditions, the study explains why effective conductivity values, giving correct results for the ISO 834 standard fire scenario, should not be used in other fire scenarios. For this reason, the thermal properties of timber given in EN 1995‐1‐2 are limited to standard fire exposure. As shown by heat transfer calculations, the effective thermal conductivity of the char layer is strongly dependent on the charring rate and therefore varies during a natural fire scenario. It has also been shown that char oxidation during the decay phase in a natural fire has a significant influence on the temperature development in the timber member, since char surface temperatures exceed the gas temperature in the compartment or furnace. Using increased effective gas temperature as thermal action during the decay phase, and varying conductivity values for the char layer, fairly good agreement could be obtained regarding the temperature development in the timber member and the char depth. Copyright © 2005 John Wiley & Sons, Ltd.

Thermal and structural performance of GRP panels and short columns under fire conditions

This paper presents the results of an experimental study of the behaviour of different types of GRP structures under fire conditions. The experiments were conducted in two stages. The first part is concerned with the thermal performance of GRP sandwich panels and stringer systems when exposed to fire on one side. The objective of this study is to provide experimental information of temperature developments in GRP structures in fire. The products examined in this investigation include: glass reinforced phenolic laminate sheets, lightweight phenolic foams, sandwich panels made from GRP sheets and phenolic foams, sandwich panels made from plasterboards and phenolic foams, stringer systems made from GRP sheets and pultruded GRP channels insulated with mineral wool and stringer systems made from plaster boards and pultruded GRP channels with mineral wool. For comparison, fire tests were also carried out on conventional steel stud systems consisting of plasterboards and cold-formed-thin-walled steel channel sections insulated with mineral wool. In all these tests, the core materials were 100 mm thick. Plasterboards were 12.5 mm thick and the GRP sheets were 3 mm thick. Fire exposure was according to the standard BS: 476 Part 20 – Cellulosic fire temperature–time relationship. The second part gives results of compressive tests on pultruded short GRP channel sections at elevated temperatures to evaluate their residual strength in fire. The objectives of these tests are to assess the feasibility of using GRP based products as wall construction in low storey buildings such as accommodation units and also to provide experimental data for the calibration of numerical models of heat transfer and structural analysis. Results of these tests indicate that the low-density phenolic foam used in this study was involved in burning very early in the fire test and would not be suitable for fire resistant construction. Initially the fire exposed thin GRP sheet could not provide as much insulation as the plasterboard, however, the GRP sheet prevented direct heating of the core material and was able to reduce the core material temperatures considerably. At 30 min of the standard fire exposure, temperatures in large parts of the GRP stringer systems were less than 100 C. For compressive tests, pultruded channel sections 100 x 30 x 4 mm by 400 mm long were heated in an electric kiln furnace to different levels of temperature and then loaded to failure in compression in a specially constructed loading facility. The test temperatures were 20, 60, 90, 120, 150, 200 and 250°C. The results of these tests indicate that GRP materials lose their strength and stiffness at relatively low temperatures, however, due to their low thermal conductivity, temperatures in large parts of the pultruded GRP channel sections were very low (less than 100°C) enabling them to carry some loads (up to 70%) under fire conditions.

Composite beams with partial fire protection

Abstract This paper presents the results of a theoretical investigation into the effectiveness of a novel way to significantly reduce the fire protection cost to a composite beam. In this method, only the steel lower flange and a fraction of the steel web are protected. The effectiveness of a partially protected composite beam is assessed by comparing its plastic moment capacity with that of a fully protected beam subject to both the standard fire exposure and design fires. The parametric time–temperature curves in Eurocode 1 are used to determine the time–temperature relationships of design fires. A finite element analysis computer program for heat transfer is used to evaluate the temperature field in the composite cross-section. The plastic moment capacity is calculated by dividing the composite cross-section into many small blocks and summing their contributions. Partial protection is suitable for situations where the protection is applied along the steel profile. Results from this study indicate that the total fire protection cost may be reduced considerably due to more than 50% reduction in the protected surface area, despite similar material costs.

Coupled heat and mass transport phenomena in siliceous aggregate concrete slabs subjected to fire

A mathematical and computational model simulating the coupled heat and mass transfer and related processes in porous media exposed to elevated temperatures has been developed. Taking into account the conservation of mass, momentum and energy, and including the effects of evaporation and dehydration processes on the transport phenomena, a set of three coupled nonlinear differential equations is obtained. Siliceous aggregate concrete slabs subjected to the ASTM E119 standard fire exposure are modeled and validated against test data. Output depicts the coupled relationships between the material's temperature, moisture content, and pore pressure histories and distributions.

Furnace heat transfer processes applied to a strategy for the fire testing of reduced scale structural models

A previous strategy for the fire testing of reduced scale structural models subject to standard fire exposure on one side is developed. The basis for the establishment of a model fire curve is articulated, which will produce equivalence of thermo-structural output between model and prototype by creating thermal distributions in the model, which are dynamically similar to that experimentally obtained in the prototype. The analysis takes into consideration the complex nature of both convective and radiative surface energy transfer between the furnace gases and specimen, utilising a one-dimensional heat transfer computer simulation, formulated on a spreadsheet. Model fire curves can be predicted on the basis of convective, radiative or mixed-mode simulations. The results of the tests indicate good similitude in thermal responses for samples scaled by 1 √2 and 1 2 .

COMPUTATIONAL HEAT AND MASS TRANSPORT IN CONCRETE WALLS EXPOSED TO FIRE

A numerical method has been developed for the prediction of coupled heat and mass transfer and related processes in porous media exposed to elevated temperatures. The computer model predictions have been validated against experimental results of carbonate aggregate concrete slabs subjected to the ASTM E119 standard fire exposure. Output from the model depicts the coupled relationships between the temperature, moisture content, and pore pressure histories and distributions. This article investigates the numerical effect of grid spacing on the pore pressure fluctuations and the influence of the pore pressure on the spalling potential of concrete exposed to elevated temperatures.

Modeling the Thermal Behavior of Concrete Slabs Subjected To the Astm E119 Standard Fire Condition

A mathematical and computational model simulating the coupled heat and mass transfer and related processes in porous media exposed to elevated temperatures has been developed. Taking into account the conservation of mass, momentum, and energy, and the evaporation of free and chemically bound water released by dehydration and their effect on the transport phenomena, a set of three coupled nonlinear differential equations is obtained. Carbonate aggregate concrete slabs subjected to the ASTM E119 standard fire exposure are modeled and validated against test data. Output depicts the coupled relationships between the material's temperature, moisture content, and pore pressure histories and distributions. Language: en

Evaluation of duct opening protection in two-hour fire walls and partitions

There is a continuing debate among fire protection specialists on the value and role of fire dampers in preventing fire spread via HVAC duct systems. It has been recognized that fire dampers are not required under all circumstances. For example, NFPA 90A,Standard for the Installation of Air Conditioning and Ventilation Systems, does not require the installation of fire dampers in ducts penetrating one-hour fire-rated walls and partitions. Additionally, there are circumstances where the closure of dampers may affect critical environmental air systems. In these situations, the value of fire dampers must be determined in terms of an overall risk assessment. It has been suggested that the role of fire dampers be considered in terms of the total building fire protection system, but a quantitative approach for such an assessment has been previously unavailable. In particular, there has been no data related to the performance of a duct system when subjected to a standard two-hour fire exposure. Gewain et al. have described an equivalency approach and full-scale fire test data for the protection of duct openings in two-hour fire-resistant walls and partitions. The objective of this paper is to review and summarize the equivalency rationale and test data and describe engineering methods available to apply an equivalency approach more generally. The approach was developed for situations where horizontal steel ventilation ducts penetrate fire-rated walls and partitions. The approach does not address smoke dampers or ducts containing combustible materials.

Impact of Fire Exposure on Heat Transmission in Concrete Slabs

The ASTM Standard E-119 specifies that when a structural component is fire-tested by exposing one surface to a standard fire exposure, the component fails if the temperature of the unexposed surface of the test component rises 250°F (130°C) or more during the rating period. The standard fire exposure usually is not representative of the compartment temperatures that develop during an actual fire, and the test results may not be indicative of how components might actually behave. In particular, the standard test may give an overly pessimistic appraisal of the behavior of concrete components greater than 76 mm (3 in.) thick and that have excellent insulating characteristics. Design economies might be achieved by allowing the use of natural fire exposures rather than one universal test in assigning fire ratings and in fire-resistant structural design.

Measuring the leakage of door assemblies during standard fire exposures

AbstractThe results of applying the tentative, high temperature, International Standards Organization test methods DP 5925 Part 3, which was developed to measure smoke leakage of door assemblies during the course of a standard fire endurance test, are reported. A critical analysis reveals that the basic objective of the test method is limited in its utility in that fire scenarios in high‐rise buildings may not be adequately simulated. Independent of this limitation, the analysis then identifies certain theoretical problems with the test method and its procedures. These lead to a conclusion that the test method is not generally reliable. An alternative test concept which appears to remove this limitation and all of its problems is described, and its development is advocated.

Fire Safety Of External Building Elements--The Design Approach

The adoption of a design approach to fire safety in buildings has gained increasing acceptance as it has become clear that the traditional rules are not always sufficiently flexible or may not be adequate to cope with modern developments in the use and construction of buildings. For elements of structure, building codes have a performance requirement based on a specified exposure period of the element to the standard fire resistance test of ASTM E119, and while it has been recognized that the building fire exposure may not be the same as the standard fire exposure, the tendency has been more to criticize the required period of fire resistance than to question the standard test conditions themselves. However, a major difficulty with the standard test has been encountered when buildings are designed with external structural steel elements. These elements are required by the codes to have the same minimum periods of fire resistance and hence the same cladding as internal elements, even though the external fire exposure conditions are known to be less severe. The fire exposure of external structural elements cannot be simulated by the standard fire resistance test, but it can be calculated. The heat transfer to these elements depends on the flame trajectory and temperature, the temperature in the fire compartment, the position of the element, and the cooling of the element to the surroundings. As for internal elements, the structural performance depends on the steel temperature, and a calculation method for estimating the temperature rise can be established. The calculation method is based on comprehensive studies with models and on a number of large scale experimental fire tests in realistic buildings. The calculated steel temperatures are in satisfactory agreement with values measured in the large-scale experimental fire tests.