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1 – 10 of over 2000Jean-Christophe Mindeguia, Guillaume Cueff, Virginie Dréan and Gildas Auguin
The fire resistance of wooden structures is commonly based on the calculation or measurement of the char layer. Designers usually estimate the char layer at the surface of a…
Abstract
Purpose
The fire resistance of wooden structures is commonly based on the calculation or measurement of the char layer. Designers usually estimate the char layer at the surface of a structural element by using analytical models. Some of these charring models can be found in regulations, as Eurocode 5. These analytical models, quite simple to use, are only reliable for the standard fire curve. In that case, the design of the structure is qualified as “prescriptive-based design” and can lead to oversizing the structure. Optimization of a structure can be achieved by using a “Performance-based design”, where realistic fire scenarios are taken into account by means of more or less complex models [parametric fires, two-zones models, computational fluid dynamics (CFD)]. For these so-called “natural fires”, no model for charring is available. The purpose of this paper is to present a novel methodology for applying a performance-based design to a simple timber structure.
Design/methodology/approach
This paper presents the development of a numerical model aiming to simulate the thermal transfer and charring in wood, under any type of thermal exposure, including non-standard fire curves. After presenting the physical background, the model is calibrated and compared to existing experimental studies on wood samples exposed to different fire curves. The model is then used as a tool for assessing the fire resistance of a common wooden structure exposed to standard and non-standard fire curves.
Findings
The results show that the fire resistance is obviously dependent on the choice of the thermal exposure. The reliability of the model is also discussed and the importance of taking into account particular reactions in wood during heating is underlined.
Originality/value
One aim of this paper is to show the opportunity to apply a performance-based approach when designing a wooden structure. It shows that more knowledge of the material behaviour under non-standard fires is still needed, especially during the decay phase.
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Lorenzo Lelli and Jonas Loutan
This paper aims to detail the advanced natural fire simulations that were carried out for the composite steel-reinforced concrete structure of the JTI Building in Geneva…
Abstract
Purpose
This paper aims to detail the advanced natural fire simulations that were carried out for the composite steel-reinforced concrete structure of the JTI Building in Geneva, Switzerland. The results of these analyses led to a significant reduction of in the fireproofing of the steel floor framing.
Design/methodology/approach
Several scenarios were studied considering different thermal behaviours of the peripheral cladding. Despite the small thickness of the resisting slabs, the analyses performed with SAFIR software showed that the typical wide storey bay (12 × 15.86 m) can resist to the design’s fire temperatures without the protection of the main and secondary beams while the spandrels remain protected. For study completeness, the composite frame-membrane model was also simulated with Hasemi-localized fire routines on SAFIR.
Findings
The analyses have showed that the membrane behaviour of composite slabs under fire allows a significant reduction of the fire protection, even in case of small thickness of the concrete topping. The increase of the reinforcement ratio to sustain the membrane forces is widely compensated by the savings related to the fireproofing of the steel framing.
Practical/implications
A natural fire approach is particularly advisable in case of fully glazed buildings. In fact when the façade collapses, the entry of a large cold air quantity limits the increase of the gas temperature inside the compartment.
Originality/value
The analyses were carried out with recent SAFIR routines for localized fires (Hasemi fire model) and represent one of the first applications in practice. The issue of the rebar orientation in mesh is raised out. The latest SAFIR release allows the definition of a global orientation of the rebars and amends the issue.
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Paulo A.G. Piloto, Carlos Balsa, Felipe Macedo Macêdo Gomes and Bergson Matias
Most of the numerical research and experiments on composite slabs with a steel deck have been developed to study the effect of fire during the heating phase. This manuscript aims…
Abstract
Purpose
Most of the numerical research and experiments on composite slabs with a steel deck have been developed to study the effect of fire during the heating phase. This manuscript aims to describe the thermal behaviour of composite slabs when submitted to different fire scenarios, considering the heating and cooling phase.
Design/methodology/approach
Three-dimensional numerical models, based on finite elements, are developed to analyse the temperatures inside the composite slab and, consequently, to estimate the fire resistance, considering the insulation criteria (I). The numerical methods developed are validated with experimental results available in the literature. In addition, this paper presents a parametric study of the effects on fire resistance caused by the thickness of the concrete part of the slab as well as the natural fire scenario.
Findings
The results show that, depending on the fire scenario, the fire resistance criterion can be reached during the cooling phase, especially for the thickest composite slabs. Based on the results, new coefficients are proposed for the original simplified model, proposed by the standard.
Originality/value
The developed numerical models allow us to realistically simulate the thermal effects caused by a natural fire in a composite slab and the new proposal enables us to estimate the fire resistance time of composite slabs with a steel deck, even if it occurs in the cooling phase.
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Daphne Pantousa and Euripidis Mistakidis
The primary purpose of this paper is the development of a fire–structure interface (FSI) model, which is referred in this study as a simplified “dual-layer” model. It is oriented…
Abstract
Purpose
The primary purpose of this paper is the development of a fire–structure interface (FSI) model, which is referred in this study as a simplified “dual-layer” model. It is oriented for design purposes, in the cases where fire-compartments exceed the “regular” dimensions, as they are defined by the guidelines of the codes (EN 1991-1-2).
Design/methodology/approach
The model can be used at the post-processing stage of computational fluid dynamics (CFD) analysis and it is based on the gas-temperature field (spatial and temporal) of the fire-compartment. To use the “dual-layer” model, first the gas-temperature (discrete) function along the height of the fire-compartment, at discrete plan–view points should be determined through the output of the CFD analysis. The model “compresses” the point data to (spatial) virtual zones, which are divided into two layers (with respect to the height of the fire-compartment) of uniform temperature: the upper (hot) layer and the lower (cold) layer.
Findings
The model calculates the temporal evolution of the gas-temperature in the fire compartment in every virtual zone which is divided in two layers (hot and cold layer).
Originality/value
The main advantage of this methodology is that actually only three different variables (height of interface upper-layer temperature and lower-layer temperature) are exported during the post-processing stage of the CFD analysis, for every virtual zone. Next, the gas-temperature can be used for the determination of the temperature profile of structural members using simple models that are proposed in EN 1993-1-2.
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ChiaYuan Shih, YaoHan Chen, ChungHwei Su, ShiuanCheng Wang and YungChang Yang
The purpose of this paper is to analyze the phenomenon of makeup effect using numerical simulation and model experiments on seven different natural smoke extraction patterns of…
Abstract
Purpose
The purpose of this paper is to analyze the phenomenon of makeup effect using numerical simulation and model experiments on seven different natural smoke extraction patterns of tall space. Airflow distribution and heat accumulation phenomenon in different cases are compared. The natural smoke exhaust system for tall spaces has many advantages, including low cost, no power and low maintenance cost. It is more advantageous than the mechanical type of exhaust. However, the internal air distribution is complicated since the large span spatial character. Effective and correct verification method is very important for the analysis of flow fields in tall spaces.
Design/methodology/approach
This study used fire dynamics simulator (FDS) software to simulate the fire scene. The model experiments are conducted to determine if the numerical simulation results are reasonable. A single-mirror Schlieren system, including an 838 (H) × 736 mm (W) square concave mirror, as well as the focal length of 3,100 mm was adopted to record the dynamic flow of hot gas. Six smokeless candles were burned in a 1/12.5 model in experiments to record the distribution of inflow, accumulation and outflow of airflow in the space. In addition, the thermocouple lines were mounted in the model for temperature measurement.
Findings
The results of numerical simulation and model experiments have proved that makeup air has a significant effect on the effectiveness of a natural smoke vent system. Larger areas of smoke vents will produce more heat accumulation phenomenon. In this study, the air inlet and vent installed on the same side have a better heat removal effect. Moreover, Schlieren photography technique is proved to be an accurate measurement method to record the dynamic flow of hot air immediately, directly and accurately. The dynamic flow behavior of hot gas in the model has been visualized in this paper.
Originality/value
At present, there is no examination method other than checking the smoke vent area to validate the effectiveness of a natural smoke vent system in Taiwan, as well as no requirements regarding the makeup inlet. The effect of makeup air in generating the effective push-pull phenomenon of airflow has been analyzed. In addition, the post-combustion hot gas distributions were visualized by using Schlieren photography technology in the model space, compared with the FDS simulation result and thermocouple recorded temperature. A verification method in the model experiments is established to determine if the numerical simulation results are reasonable.
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Thomas Gernay and Mohamed Salah Dimia
The paper aims to give an insight into the behaviour of reinforced concrete columns during and after the cooling phase of a fire. The study is based on numerical simulations as…
Abstract
Purpose
The paper aims to give an insight into the behaviour of reinforced concrete columns during and after the cooling phase of a fire. The study is based on numerical simulations as these tools are frequently used in structural engineering. As the reliability of numerical analysis largely depends on the validity of the constitutive models, the development of a concrete model suitable for natural fire analysis is addressed in the study.
Design/methodology/approach
The paper proposes theoretical considerations supported by numerical examples to discuss the capabilities and limitations of different classes of concrete models and eventually to develop a new concrete model that meets the requirements in case of natural fire analysis. Then, the study performs numerical simulations of concrete columns subjected to natural fire using the new concrete model. A parametric analysis allows for determining the main factors that affect the structural behaviour in cooling.
Findings
Failure of concrete columns during and after the cooling phase of a fire is a possible event. The most critical situations with respect to delayed failure arise for short fires and for columns with low slenderness or massive sections. The concrete model used in the simulations is of prime importance and the use of the Eurocode model would lead to unsafe results.
Practical implications
The paper includes implications for the assessment of the fire resistance of concrete elements in a performance‐based environment.
Originality/value
The paper provides original information about the risk of structural collapse during cooling.
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Waldemar Weisheim, Peter Schaumann, Lisa Sander and Jochen Zehfuß
This paper aims to deal with the experimental and numerical investigations of the fire protection performance of a waterborne intumescent coating (IC) on structural steel in case…
Abstract
Purpose
This paper aims to deal with the experimental and numerical investigations of the fire protection performance of a waterborne intumescent coating (IC) on structural steel in case of natural fires. Based on own small-scale laboratory tests, an advanced numerical model is developed to simulate the fire protection performance of the investigated coating in case of arbitrary fire scenarios. The insulation efficiency of the coating is described within the model by temperature and heating rate-dependent material properties, such as expansion factors, thermal conductivity and heat capacity. The results of the numerical model are compared to own large-scale fire tests of an unloaded I-section beam and column.
Design/methodology/approach
As natural fires can show arbitrary regimes, the material properties of the waterborne IC are investigated for various heating rates. Based on these investigations, a material model for the IC is implemented in the finite element program ABAQUS. With the help of user subroutines, the material properties of the coating are introduced for both the heating and cooling phase of natural fires, allowing for two- and three-dimensional thermomechanical analyses of coated steel elements.
Findings
The results of the performed small-scale laboratory tests show a heating rate-dependent behavior of the investigated coating. The mass loss as well as the expansion of the coating change with the heating rate. Moreover, the material properties obtained on small scale are valid for large scale. Therefore, a material model could be developed that is suitable to reproduce the results of the large-scale fire tests. Additionally, with the help of the numerical model, a dimensioning approach for the dry film thickness (DFT) of the investigated coating is derived for arbitrary natural fires.
Research limitations/implications
The material properties presented in this paper are only valid for the investigated waterborne IC and the parameter area that was chosen. However, the developed modeling approach for the fire protection performance of ICs is general and can be applied for every coating that is part of the intumescent product family.
Originality/value
Until now, only few research works have been carried out on the fire protection performance of ICs under non-standard fire exposure. This paper deals extensively with the material properties and the material modeling of a waterborne IC exposed to natural fires. Especially, the laboratory examinations and the numerical simulations are unique and allow for new evaluation possibilities of ICs.
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ChungHwei Su and ShiuanCheng Wang
The purpose of this paper is to analyze the variations in the neutral plane when a tall space with unsymmetrical openings is on fire. The neutral plane of the fire scene is an…
Abstract
Purpose
The purpose of this paper is to analyze the variations in the neutral plane when a tall space with unsymmetrical openings is on fire. The neutral plane of the fire scene is an important index of a natural smoke exhaust system. The numerical simulation method and the Schlieren photography technique were used as analysis tools. The results of model experiments and numerical simulation were compared with each other to confirm the rationality of the conclusions. The results were to discuss the characteristics of various cases and showed that the neutral planes of the fire scene were not always horizontal.
Design/methodology/approach
The numerical simulation method and the Schlieren photography technique were used as analysis tools. The flow patterns of hot air in various cases were recorded using the flow visualization technique. In addition, the renowned simulation software, fire dynamics simulator (FDS), was used for case analysis. The Schlieren photography technique was used for 1/12.5 model experiments with six smokeless candles burned, and FDS was used for a numerical simulation. In terms of the case of unilateral vents, the exhaust efficiency was discussed when the exhaust vent and air inlet were located on the same side or different sides.
Findings
This study demonstrates that makeup air flowing in from the inlets and openings has a significant impact on the effectiveness of natural smoke exhaust systems. The results illustrated that the neutral planes were tilted in some cases. In some cases, the results showed that one side was the air inlet and the other side was the exhaust vent, even if the openings were at the same height in some cases. These phenomena have rarely been discovered or studied in the past. The exhaust efficiency was not always better when the vent was located in the rooftop.
Originality/value
This study analyzed the neutral plane of a fire scene using the common unsymmetrical opening spaces in the Taiwan region as an example. The phenomenon of non-horizontal neutral plane has rarely been studied in the past. The temperature of the discharged hot gas was low because of an efficient exhaust effect, which reduced the heat and smoke storage in the space. The results obtained by these two methods were consistent, and showed that the cases with the same opening area had different smoke extraction efficiencies, meaning the smoke extraction effect cannot be judged only by the opening areas.
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Marcus Achenbach and Guido Morgenthal
The design check regarding the fire resistance of concrete slabs can be easily performed using tabulated values. These tables are based on experimental results, but the level of…
Abstract
Purpose
The design check regarding the fire resistance of concrete slabs can be easily performed using tabulated values. These tables are based on experimental results, but the level of safety, which is obtained by this approach, is not known. On the other hand, performance-based methods are more accepted, but require a target reliability as performance criterion. Hence, there is a need for calibration of the performance-based methods using the results of the “traditional” descriptive approach.
Design/methodology/approach
The calibration is performed for a single span concrete slab, where the axis distance of the reinforcement is chosen according to Eurocode 2 for a defined fire rating. A “standard” compartment is selected to cover typical fields of application. The opening factor is considered as parameter to obtain the maximum peak temperatures in the compartment. A Monte Carlo simulation, in combination with a response surface method, is set up to calculate the probabilities of failure.
Findings
The results indicate that the calculated reliability index for a standard is within the range, which has been used for the derivation of safety and combination factors in the Eurocodes. It can be observed that members designed for a fire rating R90 have a significant increase in the structural safety for natural fires compared to a design for a fire rating R30.
Originality/value
The level of safety, which is obtained by a design based on tabulated values, is quantified for concrete slabs. The results are a necessary input for the calibration of performance-based methods and could stimulate discussions among scientists and building authorities.
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Richard Walls, Celeste Viljoen, Hennie de Clercq and Charles Clifton
This paper aims to present a reliability analysis of the slab panel method (SPM) for the design of composite steel floors in severe fires. Rather than seeking to accurately define…
Abstract
Purpose
This paper aims to present a reliability analysis of the slab panel method (SPM) for the design of composite steel floors in severe fires. Rather than seeking to accurately define failure levels, this paper highlights areas of uncertainty in design and their effect on design results, whilst providing approximate reliability levels.
Design/methodology/approach
A Monte Carlo simulation has been conducted using the SPM design procedure to produce probability density functions of floor capacity for various floor layouts. Statistical input variables were obtained from the literature. Different configurations, geometries and fire severities are included to demonstrate how predicted floor capacities are influenced.
Findings
From the research presented, it is clear that the predicted reliability of SPM systems varies relative to a large number of criteria, but especially parameters related to fire loading. Predicted capacities are shown to be conservative compared to results of furnace and large-scale natural fire tests, which exhibit higher fire resistance. Due to distinct fire hazard categories with associated input values, there are step discontinuities in capacity graphs.
Originality/value
Limited research has been done to date on the reliability of structures in fire as discussed in this paper. It is important to verify the reliability levels of systems to ensure that partial and global factors of safety are adequate. Monte Carlo simulations are shown to be effective for calculating the average floor capacities and associated standard deviations. The presentation of probability density functions for composite floors in severe fires is novel.
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