| 1. |
- Possidente, Luca, et al.
(författare)
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Derivation of a new temperature calculation formulation for heavily fire insulated steel cross-sections
- 2023
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Ingår i: Fire safety journal. - : Elsevier. - 0379-7112 .- 1873-7226. ; 141
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Tidskriftsartikel (refereegranskat)abstract
- Equations are given in the Eurocode standard EN 1993-1-2 on the estimation of temperature in insulated steel cross sections when assuming uniform steel section temperature, sometimes called a lumped heat capacity assumption. When deriving these equations the temperature of the exposed insulation surface is assumed equal the surrounding fire gas temperature. That is a simplification that may provide inaccurate results for heavily insulated steel sections, when the heat capacity of the insulation is considerably higher than that of the steel section. Therefore, a new lumped mass formulation suited for heavily insulated steel sections is proposed in this paper. It accounts for the heat transfer resistance between the fire and the insulation surface as well as for the heat capacity of the insulation. The accuracy of the predictions made with the proposed new formulation are compared with results of accurate 1-D finite element numerical analyses considering insulation materials with several combinations of thermal properties and thicknesses. Analyses with the proposed formulation is shown to yield accurate and generally on the safe side estimations of steel temperature in comparison to the finite element (FE) calculations. The new formulation is applicable to lightly as well as heavily insulated steel sections.
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| 2. |
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| 3. |
- Sandström, Joakim, Teknisk licentiat, 1979-, et al.
(författare)
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Thermal exposure from localized fires to horizontal surfaces below the hot gas layer
- 2019
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The temperature in the lower chord of steel trusses subjected to localized fires is difficult to estimate as most thermal exposure correlation formulas presented in the literature focus on heating along the ceiling where the temperature is very different from that of the lower chord [1], [2]. At the same time as the upper chord is engulfed in a ceiling jet from a localized fire, the lower chord may be surrounded by air at ambient temperature.Two existing methods by Zhang and Usmani [3] and Guowei et al. [4], [5] along with one new approach for calculating the thermal exposure of the lower chord are presented in this paper and compared to the results from experiments conducted in Trondheim 2015 [6].A new approach presented in this paper is evaluated based on two separate assumptions of the thermal exposure. Outside the plume, the radiative contribution is assumed originating from the plume in the form of a cylinder and inside the plume, the temperature is assumed decreasing according to a Gaussian shape from the central axis temperature to the temperature down to the temperature from the first part of the model at the transition between inside and outside the plume.All models provide good correlation to the experimental data outside the plume perimeter. Inside the plume perimeter, the thermal impact depends to a high degree to the relation between the flame height and the height of the horizontal surface of interest.
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| 4. |
- Wickström, Ulf, et al.
(författare)
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Measuring incident heat flux and adiabatic surface temperature with plate thermometers in ambient and high temperatures
- 2019
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Ingår i: Fire and Materials. - : Wiley. - 0308-0501 .- 1099-1018. ; 43:1, s. 51-56
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Tidskriftsartikel (refereegranskat)abstract
- A new more insulated and faster responding plate thermometer (PT) is introduced,which has been developed for measurements particularly in air at ambient temperature.It is a cheaper and more practical alternative to water‐cooled heat flux meters(HFMs). The theory and use of PTs measuring incident radiation heat flux and adiabaticsurface temperature are presented. Comparisons of measurements with PTsand HFMs are made. Finally, it is concluded that incident radiation in ambient aircan be measured with HFMs as well as with the new insulated type of PT. In hot gasesand flames, however, only PTs can be recommended. At elevated gas temperatures,convection makes measurements with HFMs difficult to interpret and use for calculations.However, they can be used in standard or well‐defined configurations forcomparisons.
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| 5. |
- Byström, Alexandra, et al.
(författare)
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Temperature of post-flashover compartment fires : calculations and validation
- 2018
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Ingår i: Fire and Materials. - : John Wiley & Sons. - 0308-0501 .- 1099-1018. ; 42:3, s. 255-265
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes and validates by comparisons with tests a one-zone model for computing temperature of fully developed compartment fires. The model is based on an analysis of the energy and mass balance assuming combustion being limited by the availability of oxygen, i.e. ventilation controlled fire. It is demonstrated that the model can be used to predict fire temperatures in compartments with semi-infinitely thick boundaries as well as with boundaries of insulated and uninsulated steel sheets where the entire heat capacity of the surrounding structure is assumed to be concentrated to the steel core. That is so called lumped heat capacity is assumed.When developing the fire model a maximum fire temperature was defined depending on combustion efficiency and opening heights only. This temperature was then used as a thermal boundary condition to calculate the temperature of the surrounding structure. The fire temperature was then derived to be a weighted average between the maximum fire temperature and the current calculated surrounding structure surface temperature.A general finite element solid temperature calculation code (TASEF) was used to calculate the temperature in the boundary structure. With this code it is possible to analyze surrounding structures of various kinds comprising materials with properties varying with temperature as well as assemblies of various materials.The experiments referred to were accurately defined and surveyed. In all the tests a propane diffusion burner was used as the only fire source. Temperatures were measured with thermocouples and plate thermometers at several positions [1].
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| 6. |
- Lange, David, et al.
(författare)
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The Tisova fire test part 2: heat transfer analysis
- 2018
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report is the second of two reports into the Tisova fire test. It compares the results of three different groups’ attempts to model the temperature response of the structure in Tisova which was subject to a large scale travelling fire test. Generally it is observed that the different approaches have relatively close results, although one shows systematically hotter temperatures closer to the heated surface than the others; and differences between all three increase further from the heated surface.A comparison between the average calculated results and the experimental results is also shown for illustration. While an absolute comparison is not attempted because of experimental errors present the results do show the possible need for further data to support the heat transfer analysis required to carry out structural design for travelling fires.
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| 7. |
- Schmid, Joachim, et al.
(författare)
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Timber under real fire conditions - the influence of oxygen content and gas velocity on the charring behavior
- 2018
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Ingår i: Journal of Structural Fire Engineering. - : Emerald Group Publishing Limited. - 2040-2317 .- 2040-2325. - 9781605953205 ; 9:3, s. 222-236
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Tidskriftsartikel (refereegranskat)abstract
- Purpose – The purpose of this study is to investigate the influencing factors on the charring behaviour of timber, the char layer and the charring depth in non-standard fires. Design/methodology/approach – This paper summarizes outcomes of tests, investigating the influences on the charring behavior of timber by varying the oxygen content and the gas velocity in the compartment. Results show that charring is depending on the fire compartment temperature, but results show further that at higher oxygen flow, char contraction was observed affecting the protective function of the char layer. Findings – In particular, in the cooling phase, char contraction should be considered which may have a significant impact on performance-based design using non-standard temperature fire curves where the complete fire history including the cooling phase has to be taken into account. Originality/value – Up to now, some research on non-standard fire exposed timber member has been performed, mainly based on standard fire resistance tests where boundary conditions as gas flow and oxygen content especially in the decay phase are not measured or documented. The approach presented in this paper is the first documented fire tests with timber documenting the data required.
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| 8. |
- Wickström, Ulf, et al.
(författare)
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Technical comment : ten fundamental principles on defining and expressing thermal exposure as boundary conditions in fire safety engineering
- 2018
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Ingår i: Fire and Materials. - : John Wiley & Sons. - 0308-0501 .- 1099-1018. ; 42:8, s. 985-988
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Tidskriftsartikel (refereegranskat)abstract
- Predicting the temperature of an exposed object or even a person is one of the most common tasks of fire safety engineering. However, the nonlinear nature of heat transfer and the challenge of changing material properties with temperature have plagued precise predictions. In addition, as methodologies are developed, one of the biggest challenges is to apply them to known scenarios where temperatures and heat fluxes have been measured. The interpretations of such measurements are, however, often clouded by the lack of common understanding of the reported values and how they shall be translated into boundary conditions to be used for calculations. This technical comment summarizes the Fundamental Principles that are crucial to properly identifying the fire exposure so that appropriate temperature predictions can be made.
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| 9. |
- Byström, Alexandra
(författare)
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Compartment Fire Temperature Calculations and Measurements
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is devoted to heat transfer and fire dynamics in enclosures. It consists of a main part which summarizes and discusses the theory of heat transfer, conservation of energy, fire dynamics and specific fire scenarios that have been studied. In the second part of this thesis, the reader will find an Appendix containing seven scientific publications in this field.In particular, one- and two-zone compartment fire models have been studied. A new way of calculating fire temperatures of pre- and post-flashover compartment fires is presented. Three levels of solution techniques are presented including closed form analytical expressions, spread-sheet calculations and solutions involving general finite element temperature calculations. Validations with experiments have shown good accuracy of the calculation models and that the thermal properties of the surrounding structures have a great impact on the fire temperature development. In addition, the importance of the choice of measurement techniques in fire engineering has been studied. Based on the conclusions from these studies, the best techniques have been used in further experimental studies of different fire scenarios.
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| 10. |
- Sandström, Joakim, 1979-, et al.
(författare)
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The Life Safety Objective in Performance-Based Design for Structural Fire Safety
- 2017
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Konferensbidrag (refereegranskat)abstract
- Structural stability is not necessarily required for buildings where life safety is the sole structural fire safety objective. However, a structural collapse is only acceptable in an area where lethal fire conditions have developed. Therefore, structural failures due to fire resulting in risks of progressing outside of the area of lethal fire conditions need to be addressed. Thus, a new type of design principles for the life safety objectives is presented here which enables an evaluation of more precise risk assessments and more cost-efficient solutions without compromising human safety.
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