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  • 301.
    Wickström, Ulf
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Steady-State Conduction2016Inngår i: Temperature Calculation in Fire Safety Engineering, Encyclopedia of Global Archaeology/Springer Verlag, 2016, s. 17-24Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    In one dimension in the x-direction the rate of heat transfer or heat flux is expressed according to Fourier’s law as outlined in Sect. 1.​1.q . ′′ x =−k⋅dTdx q.x′′=−k⋅dTdxwhere k is the thermal conductivity. For simplicity the mathematical presentation of the heat transfer phenomena is here in general made for one-dimensional cases only. Corresponding presentations in two and three dimensions can be found in several textbooks such as [1, 2].

  • 302.
    Wickström, Ulf
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Temperature Calculation in Fire Safety Engineering2016Bok (Fagfellevurdert)
    Abstract [en]

    This book provides a consistent scientific background to engineering calculation methods applicable to analyses of materials reaction-to-fire, as well as fire resistance of structures. Several new and unique formulas and diagrams which facilitate calculations are presented. It focuses on problems involving high temperature conditions and, in particular, defines boundary conditions in a suitable way for calculations. A large portion of the book is devoted to boundary conditions and measurements of thermal exposure by radiation and convection. The concepts and theories of adiabatic surface temperature and measurements of temperature with plate thermometers are thoroughly explained.Also presented is a renewed method for modeling compartment fires, with the resulting simple and accurate prediction tools for both pre- and post-flashover fires. The final chapters deal with temperature calculations in steel, concrete and timber structures exposed to standard time-temperature fire curves. Useful temperature calculation tools are included, and several examples demonstrate how the finite element code TASEF can be used to calculate temperature in various configurations. Temperature Calculation in Fire Safety Engineering is intended for researchers, students, teachers, and consultants in fire safety engineering. It is also suitable for others interested in analyzing and understanding fire, fire dynamics, and temperature development. Review questions and exercises are provided for instructor use.

  • 303.
    Wickström, Ulf
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Temperature of Steel Structures2016Inngår i: Temperature Calculation in Fire Safety Engineering, Encyclopedia of Global Archaeology/Springer Verlag, 2016, s. 195-216Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    Steel is sensitive to high temperature. The critical temperature of a steel member is the temperature at which it cannot safely support its load.

  • 304.
    Wickström, Ulf
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Temperature of Timber Structures2016Inngår i: Temperature Calculation in Fire Safety Engineering, Encyclopedia of Global Archaeology/Springer Verlag, 2016, s. 227-233Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    Modelling the thermal behaviour of wood is complicated as phenomenas such as moisture vaporization and migration, and the formation of char have decisive influences on the temperature development within timber structures. Nevertheless it has been shown that general finite element codes can be used to predict temperature in, for example, fire-exposed cross sections of glued laminated beams [52], provided, of course, that apparent thermal material properties and appropriate boundary conditions are used. Other specialized numerical codes for timber structures have been developed, e.g. by Fung

  • 305.
    Wickström, Ulf
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Temperatures of Concrete Structures2016Inngår i: Temperature Calculation in Fire Safety Engineering, Encyclopedia of Global Archaeology/Springer Verlag, 2016, s. 217-225Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    Reinforced concrete structures are sensitive to fire exposure of mainly two reasons. They may be subject to explosive spalling, and they may lose their load-bearing capacity due to high temperatures. Spalling is particularly hazardous as it may occur more or less abruptly and unanticipated. It usually starts within 30 min of severe fire exposure. It may depend on several mechanisms or combinations thereof such as pore pressure, stresses due to temperature gradients, differences of thermal dilatation and chemical degradations at elevated temperatures. Reinforcement bars of steel lose their strength at temperature levels above 400 °C. Prestressed steel may even loose strength below that level. Concrete loose as well both strength and stiffness at elevated temperature.

  • 306.
    Wickström, Ulf
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Thermal Ignition Theory2016Inngår i: Temperature Calculation in Fire Safety Engineering, Encyclopedia of Global Archaeology/Springer Verlag, 2016, s. 125-132Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    The various aspects of the subject ignition of unwanted fires has been thoroughly investigated by Babrauskas and presented in the comprehensive Ignition Handbook. This book is concentrating on the calculation of the development of surface temperature. Despite many limitations, it is often assumed that a solid ignites due to external heating when its exposed surface reaches a particular ignition temperature.

  • 307.
    Wickström, Ulf
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Unsteady-State Conduction2016Inngår i: Temperature Calculation in Fire Safety Engineering, Encyclopedia of Global Archaeology/Springer Verlag, 2016, s. 25-44Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    When a body is exposed to unsteady or transient thermal conditions, its temperature changes gradually, and if the exposure conditions remain constant it will eventually come to a new steady state or equilibrium. The rate of this process depends on the mass and thermal properties of the exposed body, and on the heat transfer conditions. As a general rule the lighter a body is (i.e. the less mass) and the larger its surface is, the quicker it adjusts to a new temperature level, and vice versa. The temperature development is governed by the heat conduction equation (Eq. 1.29) with the assigned boundary conditions. It can be solved analytically in some cases, see textbooks such as [1, 2], but usually numerical methods are needed. This is particular the case in fire protection engineering problems where temperature generally varies over a wide range, often several hundred degrees.

  • 308.
    Wickström, Ulf
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Anderson, Johan
    RISE Research Institutes of SwedenBorås, Sweden.
    Sjöström, Johan
    RISE Research Institutes of SwedenBorås, Sweden.
    Measuring incident heat flux and adiabatic surface temperature with plate thermometers in ambient and high temperatures2019Inngår i: Fire and Materials, ISSN 0308-0501, E-ISSN 1099-1018, Vol. 43, nr 1, s. 51-56Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 309.
    Wickström, Ulf
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Byström, Alexandra
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Sjöström, Johan
    SP Sveriges Tekniska Forskningsinstitut, Brandteknik.
    Temperature measurements and modelling of flashed over compartment fires2016Inngår i: Proceedings of 14th International Conference and Exhibition on Fire Science and Engineering, 2016, Vol. 2, s. 949-960, artikkel-id 12Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper describes and validates by comparisons with test results a one-zone model for computing temperatures of compartment fires where flashover is reached. The model is based on an analysis of the energy and mass balance of a fully developed (ventilation controlled) compartment fire. It is demonstrated in this paper that the model can be used to predict fire temperatures in compartments with semi-infinite boundaries as well as with boundaries of insulated or uninsulated steel sheets where so called lumped heat capacity can be assumed. Comparisons are made with a series of experiments in compartments of light weight concrete, and insulated and non-insulated single sheet steel structures. A general finite element code has been used to calculate the temperature in the surrounding structures. The in this manner calculated surface temperatures yield the fire temperature as a function of time. By using a numerical tool like a finite element code it is possible to analyse fire compartment surrounding structures of various kinds and combinations of materials.Two new characteristic compartment fire temperatures have been introduced in this paper. They are the ultimate compartment fire temperature, which is the temperature reached when heat losses to surrounding structures as well radiation out through openings can be neglected, and the maximum compartment fire temperature, which is the temperature when only the losses to surrounding structures are neglected.The experiments referred to were accurately defined and surveyed. In all the tests a propane gas burner was used as the only fire source. Temperatures were measured with thermocouples and plate thermometers at several positions, and oxygen concentrations were measured in the fire compartment only opening. In some tests the heat release rate as well as the CO2 and CO concentrations were measured as well (Sjöström, et al., 2016).

  • 310.
    Wickström, Ulf
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Hunt, Sean
    JENSEN HUGHES.
    Lattimer, Brian
    JENSEN HUGHES.
    Barnett, Jonathan
    RED Fire Engineers Pty Ltd.
    Beyler, Craig
    JENSEN HUGHES .
    Technical comment: ten fundamental principles on defining and expressing thermal exposure as boundary conditions in fire safety engineering2018Inngår i: Fire and Materials, ISSN 0308-0501, E-ISSN 1099-1018, Vol. 42, nr 8, s. 985-988Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 311.
    Yahia Darwish, Savo
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Skog, Richard
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Suppressing Torsional Buckling Effects of Angle Members: Application on lattice towers2017Independent thesis Advanced level (professional degree), 300 hpOppgave
    Abstract [en]

    Wind towers are a today under a global development and many countries put more focus on this environmentally friendly way of producing electricity. The performance requirement increase and at the same time the wind towers should be economical. One way of achieving better performance is to build higher towers which increase the harvesting efficiency. One way of achieving high towers is to use a lattice structure. High lattice towers require more material and have a more demanding structural design. By using cold form steel angles as columns for the lattice tower the aim is to achieve a high utilization ratio of the steel angels. Angle members are susceptible to torsional buckling, which is often the critical mode. It is thus essential to enhance their torsional response.

    The four columns in a lattice tower are restrained against sideway displacements by the braces and diagonals, which limits their flexural bucking length. In contrast, restraining the torsional rotations is challenging. As angels are susceptible to torsion and the flexural buckling length is decreased, the flexural-torsional interaction becomes significant.

    The objective of this study is to investigate thin walled angle members under compression. The idea for this project is to increase the torsional properties of an angle by lacing together the free ends of its two legs. If the lacing acts like a plate the angle columns can behave similar to a closed section.  The aim will be to increase the buckling resistance of the angle column. The design is assessed through GMNIA investigations in the FEM program Abaqus and compare laced columns to their unlaced counterparts. Using this method the result will show how the buckling resistance and buckling mode is affected by the lacing.

    The results of this study showed that lacing had a positive effect on columns in cross-section class 4. Columns in these two classes reached a higher buckling resistance and the buckling mode shifted from torsional buckling to localized buckling. The result showed increased effect by using a higher density of lacing.

  • 312.
    Öhman, Kristoffer
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    The Crocodile Nose Connection: Design and laboratory tests on a novel connection for structural hollow sections2018Independent thesis Advanced level (professional degree), 20 poäng / 30 hpOppgave
    Abstract [en]

    The great properties and clear form makes the circular hollow section (CHS) appreciated by architects. When connecting these sections today it is common to use gusset plates. The knifeplate connection where the gusset plate is inserted into a slot made at the end of a circular section, is the most used connection today. This type of connections is not seen as aesthetically pleasingby architects because of its abrupt cut of the CHS.

    An alternative for the knife-plate connection is the Crocodile nose connection (CN-connection). The benefits of the CN-connection is the absence of the abrupt cut and the protruding gusset plate, which makes it appreciated by architects. In this connection the CHS’s ends are tapered, which creates two semi-elliptical cuts at both sides of the member. On these cuts, appropriate plates arefillet welded. These plates are shaped and bended so that when they are welded in place, the orientation of the extending part is parallel to the member axis. A gap is made between the extending parts so that a gusset plate can be inserted and bolted together with the member.

    Four different specimens of the CN-connection are tested in order to find the best shape. Two specimens have a stiffener between the plates, at a small distance from the end of the CHS. The difference between the presence of a stiffener and the lack of it, is investigated. The results showed that the specimens with the connecting piece obtained a much higher ultimate load, up to 413 %higher. Two different angles of the CHS’s cut is also investigated in order to see the most appropriate bevelling angle. In this case the results showed that the specimens with the smaller bevelling angle obtained a higher ultimate load, up to 40 % higher. A check of the weld connecting the plates and the CHS is also performed. This check was made with an assumed calculation model. The results showed that the calculation model only was valid for the specimens without the connecting piece. The calculation model must therefore be enhanced, in order to work for all dimensioning cases.

4567 301 - 312 of 312
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