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Wickström, Ulf
Publications (10 of 49) Show all publications
Wickström, U., Anderson, J. & Sjöström, J. (2019). Measuring incident heat flux and adiabatic surface temperature with plate thermometers in ambient and high temperatures. Fire and Materials, 43(1), 51-56
Open this publication in new window or tab >>Measuring incident heat flux and adiabatic surface temperature with plate thermometers in ambient and high temperatures
2019 (English)In: Fire and Materials, ISSN 0308-0501, E-ISSN 1099-1018, Vol. 43, no 1, p. 51-56Article in journal (Refereed) Published
Abstract [en]

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 adiabatic surface temperature are presented. Comparisons of measurements with PTs and HFMs are made. Finally, it is concluded that incident radiation in ambient air can be measured with HFMs as well as with the new insulated type of PT. In hot gases and 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 for comparisons.

Place, publisher, year, edition, pages
John Wiley & Sons, 2019
National Category
Building Technologies
Research subject
Steel Structures
Identifiers
urn:nbn:se:ltu:diva-70420 (URN)10.1002/fam.2667 (DOI)000454930200005 ()2-s2.0-85052442711 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-01-25 (johcin)

Available from: 2018-08-15 Created: 2018-08-15 Last updated: 2019-01-25Bibliographically approved
Wickström, U., Hunt, S., Lattimer, B., Barnett, J. & Beyler, C. (2018). Technical comment: ten fundamental principles on defining and expressing thermal exposure as boundary conditions in fire safety engineering. Fire and Materials, 42(8), 985-988
Open this publication in new window or tab >>Technical comment: ten fundamental principles on defining and expressing thermal exposure as boundary conditions in fire safety engineering
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2018 (English)In: Fire and Materials, ISSN 0308-0501, E-ISSN 1099-1018, Vol. 42, no 8, p. 985-988Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
John Wiley & Sons, 2018
Keywords
boundary, conditions, fire, heat flux, measurements, temperature
National Category
Building Technologies
Research subject
Steel Structures
Identifiers
urn:nbn:se:ltu:diva-70207 (URN)10.1002/fam.2660 (DOI)000449681900011 ()2-s2.0-85050489763 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-11-29 (inah)

Available from: 2018-08-06 Created: 2018-08-06 Last updated: 2019-09-13Bibliographically approved
Byström, A. & Wickström, U. (2018). Temperature of post-flashover compartment fires: calculations and validation. Fire and Materials, 42(3), 255-265
Open this publication in new window or tab >>Temperature of post-flashover compartment fires: calculations and validation
2018 (English)In: Fire and Materials, ISSN 0308-0501, E-ISSN 1099-1018, Vol. 42, no 3, p. 255-265Article in journal (Refereed) Published
Abstract [en]

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].

Place, publisher, year, edition, pages
John Wiley & Sons, 2018
National Category
Other Engineering and Technologies not elsewhere specified Building Technologies
Research subject
Steel Structures
Identifiers
urn:nbn:se:ltu:diva-59976 (URN)10.1002/fam.2488 (DOI)000435478400002 ()2-s2.0-85036594930 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-03-09 (andbra)

Available from: 2016-10-26 Created: 2016-10-26 Last updated: 2018-08-15Bibliographically approved
Schmid, J., Santomaso, A., Brandon, D., Wickström, U. & Frangi, A. (2018). Timber under Real Fire Conditions: the influence of oxygen content and gas velocity on the charring behavior. Journal of Structural Fire Engineering, 9(3), 222-236
Open this publication in new window or tab >>Timber under Real Fire Conditions: the influence of oxygen content and gas velocity on the charring behavior
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2018 (English)In: Journal of Structural Fire Engineering, ISSN 2040-2317, E-ISSN 2040-2325, Vol. 9, no 3, p. 222-236Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Emerald Group Publishing Limited, 2018
National Category
Building Technologies
Research subject
Steel Structures
Identifiers
urn:nbn:se:ltu:diva-65742 (URN)10.1108/JSFE-01-2017-0013 (DOI)000447009300004 ()2-s2.0-85033589274 (Scopus ID)978-1-60595-320-5 (ISBN)
Note

Validerad;2018;Nivå 2;2018-10-12 (johcin)

Available from: 2017-09-20 Created: 2017-09-20 Last updated: 2018-12-07Bibliographically approved
Sandström, J., Wickström, U., Thelandersson, S. & Lagerqvist, O. (2017). The Life Safety Objective in Performance-Based Design for Structural Fire Safety. In: : . Paper presented at 2nd international conference on structural safety under fire & blast loading, CONFAB 2017, London, 10-12 september 2017.
Open this publication in new window or tab >>The Life Safety Objective in Performance-Based Design for Structural Fire Safety
2017 (English)Conference paper, Published paper (Refereed)
Abstract [en]

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.

National Category
Building Technologies
Research subject
Steel Structures
Identifiers
urn:nbn:se:ltu:diva-70093 (URN)
Conference
2nd international conference on structural safety under fire & blast loading, CONFAB 2017, London, 10-12 september 2017
Funder
SBUF - Sveriges Byggindustriers Utvecklingsfond, 13330
Available from: 2018-07-09 Created: 2018-07-09 Last updated: 2019-04-16Bibliographically approved
Wickström, U. (2016). Boundary Conditions in Fire Protection Engineering (ed.). In: (Ed.), (Ed.), Temperature Calculation in Fire Safety Engineering: (pp. 45-64). Paper presented at . : Encyclopedia of Global Archaeology/Springer Verlag
Open this publication in new window or tab >>Boundary Conditions in Fire Protection Engineering
2016 (English)In: Temperature Calculation in Fire Safety Engineering, Encyclopedia of Global Archaeology/Springer Verlag, 2016, p. 45-64Chapter in book (Refereed)
Abstract [en]

A summary of the three kinds of boundary conditions as outlined in Sect. 1.​1.​3 is shown in Table 4.1. The third kind of BC sometimes called natural BC is by far the most important and common boundary condition in fire protection engineering, while the first and second kinds of BCs can rarely be specified. The third kind of BC may be divided into three subgroups, (a), (b) and (c). The subgroup (b) and (c) are particularly suitable for fire engineering applications. Subgroup (a) is applied when the heat transfer coefficient may be assumed constant as assumed in Chaps. 2 and 3. T g is then the surrounding gas temperature. In fire protection engineering it is, however, generally not accurate enough to assume a constant heat transfer coefficient as in particular heat transfer by radiation is highly non-linear, i.e. the heat transfer coefficient varies with the surface temperature. Therefore the subgroups (3b) and (3c) are the most commonly applied. They consist of a radiation term and a convection term with the corresponding emissivity ε and convection heat transfer coefficient h, respectively. The subgroup (3b) presupposes a uniform temperature T f , i.e. the radiation temperature and the gas temperature are equal. This is assumed, for example, when applying time–temperature design curves according to standards such as ISO 834 or EN 1363-1 for evaluating the fire resistance of structures, see Chap. 12. The subgroup (3c) is a more general version of (3b) as it allows for different gas T g and radiation T r temperatures, so-called mixed boundary conditions. Alternatively σ⋅T 4 r σ⋅Tr4 may be replaced by an equivalent specified incident radiation q . ′′ inc q.inc′′ according to the identity q . ′′ inc ≡σ⋅T 4 r q.inc′′≡σ⋅Tr4 (Eq. 1.​17). As shown in Sect. 4.4 all boundary conditions of subgroup 3 may be written as type 3a. That means momentarily a single effective temperature named the adiabatic surface temperature (AST) with a value between the radiation and gas temperatures as well as a corresponding total heat transfer coefficient can always be defined, see Sect. 4.4.

Place, publisher, year, edition, pages
Encyclopedia of Global Archaeology/Springer Verlag, 2016
National Category
Building Technologies
Research subject
Steel Structures
Identifiers
urn:nbn:se:ltu:diva-20148 (URN)10.1007/978-3-319-30172-3_4 (DOI)261553f2-89f7-44ba-879d-c339a250a5ea (Local ID)978-3-319-30170-9 (ISBN)978-3-319-30172-3 (ISBN)261553f2-89f7-44ba-879d-c339a250a5ea (Archive number)261553f2-89f7-44ba-879d-c339a250a5ea (OAI)
Note
Godkänd; 2016; 20160601 (andbra)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-08-15Bibliographically approved
Wickström, U. (2016). Fire Exposure of Structures According to Standards (ed.). In: (Ed.), (Ed.), Temperature Calculation in Fire Safety Engineering: (pp. 185-193). Paper presented at . : Encyclopedia of Global Archaeology/Springer Verlag
Open this publication in new window or tab >>Fire Exposure of Structures According to Standards
2016 (English)In: Temperature Calculation in Fire Safety Engineering, Encyclopedia of Global Archaeology/Springer Verlag, 2016, p. 185-193Chapter in book (Refereed)
Abstract [en]

When exposed to fire structures deform and lose load-bearing capacity which must be considered in design processes. It is then exposures to the more severe fires which are of interest such as post-flashover compartment fires and large flames for longer times. Pre-flashover fires do in general not create thermal conditions that can jeopardize the function of structural elements in a building. For design purposes it is therefore in general exposures relevant for post-flashover compartment fires that are specified in various standards and guidelines in the form of time–temperature curves. These curves are then used for controlling fire resistance test furnaces, see Fig. 12.1.

Place, publisher, year, edition, pages
Encyclopedia of Global Archaeology/Springer Verlag, 2016
National Category
Building Technologies
Research subject
Steel Structures
Identifiers
urn:nbn:se:ltu:diva-21180 (URN)10.1007/978-3-319-30172-3_12 (DOI)c0a43ddb-c957-4423-badf-43ccda3676b1 (Local ID)978-3-319-30170-9 (ISBN)978-3-319-30172-3 (ISBN)c0a43ddb-c957-4423-badf-43ccda3676b1 (Archive number)c0a43ddb-c957-4423-badf-43ccda3676b1 (OAI)
Note
Godkänd; 2016; 20160601 (andbra)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-08-15Bibliographically approved
Wickström, U. (2016). Heat Transfer by Convection (ed.). In: (Ed.), (Ed.), Temperature Calculation in Fire Safety Engineering: (pp. 89-105). Paper presented at . : Encyclopedia of Global Archaeology/Springer Verlag
Open this publication in new window or tab >>Heat Transfer by Convection
2016 (English)In: Temperature Calculation in Fire Safety Engineering, Encyclopedia of Global Archaeology/Springer Verlag, 2016, p. 89-105Chapter in book (Refereed)
Abstract [en]

In previous chapters heat transfer by convection or just convection was treated only to the extent that it provides a linear boundary condition of the 3rd kind for conduction problems when the heat transfer coefficient is assumed constant. In this chapter the physical phenomenon of convection is described in more detail.

Place, publisher, year, edition, pages
Encyclopedia of Global Archaeology/Springer Verlag, 2016
National Category
Building Technologies
Research subject
Steel Structures
Identifiers
urn:nbn:se:ltu:diva-21072 (URN)10.1007/978-3-319-30172-3_6 (DOI)aeaa0faa-7888-4e0a-bf20-efd20ba69e7f (Local ID)978-3-319-30170-9 (ISBN)978-3-319-30172-3 (ISBN)aeaa0faa-7888-4e0a-bf20-efd20ba69e7f (Archive number)aeaa0faa-7888-4e0a-bf20-efd20ba69e7f (OAI)
Note
Godkänd; 2016; 20160601 (andbra)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-08-15Bibliographically approved
Wickström, U. (2016). Heat Transfer by Radiation (ed.). In: (Ed.), (Ed.), Temperature Calculation in Fire Safety Engineering: (pp. 65-87). Paper presented at . : Encyclopedia of Global Archaeology/Springer Verlag
Open this publication in new window or tab >>Heat Transfer by Radiation
2016 (English)In: Temperature Calculation in Fire Safety Engineering, Encyclopedia of Global Archaeology/Springer Verlag, 2016, p. 65-87Chapter in book (Refereed)
Abstract [en]

Heat transfer by thermal radiation is transfer of heat by electromagnetic waves. It is different from conduction and convection as it requires no matter or medium to be present. The radiative energy will pass perfectly through vacuum as well as clear air. While the conduction and convection depend on temperature differences to approximately the first power, the heat transfer by radiation depends on the differences of the individual body surface temperatures to the fourth power. Therefore the radiation mode of heat transfer dominates over convection at high temperature levels as in fires. Numerical applications of radiation heat transfer in FSE are outlined in Sect. 4.​1.

Place, publisher, year, edition, pages
Encyclopedia of Global Archaeology/Springer Verlag, 2016
National Category
Building Technologies
Research subject
Steel Structures
Identifiers
urn:nbn:se:ltu:diva-19960 (URN)10.1007/978-3-319-30172-3_5 (DOI)0992b7fb-7caa-4f3e-bce1-ed9ffd34bad0 (Local ID)978-3-319-30170-9 (ISBN)978-3-319-30172-3 (ISBN)0992b7fb-7caa-4f3e-bce1-ed9ffd34bad0 (Archive number)0992b7fb-7caa-4f3e-bce1-ed9ffd34bad0 (OAI)
Note
Godkänd; 2016; 20160601 (andbra)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-08-15Bibliographically approved
Wickström, U. (2016). Introduction (ed.). In: (Ed.), (Ed.), Temperature Calculation in Fire Safety Engineering: (pp. 1-16). Paper presented at . : Encyclopedia of Global Archaeology/Springer Verlag
Open this publication in new window or tab >>Introduction
2016 (English)In: Temperature Calculation in Fire Safety Engineering, Encyclopedia of Global Archaeology/Springer Verlag, 2016, p. 1-16Chapter in book (Refereed)
Abstract [en]

Temperature is the dominating factor in determining the rate and extent of chemical reactions including breakdown of organic compounds and deteriorations of strength and stiffness of structural materials such as steel and concrete. Phase change phenomena including ignition as well as severe loss of strength of materials are often related to specific elevated temperature levels. Temperatures of fire gases are also of crucial importance as they initiate gas movements thereby spread of smoke and toxic fire gases. Fire temperatures vary typically over several hundred degrees. Therefore a number of thermal phenomena need special attention such as phase changes of materials and heat transfer by radiation when calculating temperature of fire-exposed materials.

Place, publisher, year, edition, pages
Encyclopedia of Global Archaeology/Springer Verlag, 2016
National Category
Building Technologies
Research subject
Steel Structures
Identifiers
urn:nbn:se:ltu:diva-21394 (URN)10.1007/978-3-319-30172-3_1 (DOI)e2ad5d68-4de1-4f99-90f6-8b21273378ae (Local ID)978-3-319-30170-9 (ISBN)978-3-319-30172-3 (ISBN)e2ad5d68-4de1-4f99-90f6-8b21273378ae (Archive number)e2ad5d68-4de1-4f99-90f6-8b21273378ae (OAI)
Note
Godkänd; 2016; 20160601 (andbra)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-08-15Bibliographically approved
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