The essence of performance-based structural fire safety design of steel building structures is the ability to predict thermal and structural response to fire. An important aspect of such predictions is the ability to evaluate strength of columns at elevated temperatures. Columns are critical structural elements, and failure of columns can lead to collapse of a structure. The ability of steel columns to carry their design loads is greatly affected by timeand temperature-dependent mechanical properties of steel at high temperatures due to fire. It is well known that structural steel loses strength and stiffness with temperature, especially at temperatures above 400 °C. Further, the reductions in strength and stiffness of steel are also dependent on the duration of exposure to elevated temperatures. The time-dependent response or creep of steel plays a particularly important role in predicting the collapse load of steel columns subjected to fire temperatures. Specifically, creep of steel leads to the creep buckling phenomenon, where the critical buckling load for a steel column depends not only on slenderness and temperature, but also on duration of exposure to fire temperatures. The main focus of the research summarized in this dissertation is on a testing program to investigate the effects of time-dependent material behavior or creep on buckling of steel columns subjected to fire. Material characterization tests were conducted at temperatures up to 1000 °C to evaluate tensile and creep properties of ASTM A992 steel at elevated temperatures. In addition, buckling tests on W4×13 wide flange columns under pin-end conditions were conducted to characterize short-time and vii creep buckling phenomena at elevated temperatures. The column test results are further used to verify analytical and computational tools developed to model the time-dependent buckling of steel columns at elevated temperatures. Test results are also compared against code-based predictions such as those from Eurocode 3 and the AISC Specification. Results of the research study presented in this dissertation clearly indicate that thermal creep of steel has a very large effect on strength of steel columns at high temperatures due to fire. The effect of creep on column capacity at high temperatures can be predicted using analytical and computational approaches presented in this dissertation. / text

This thesis presents the results of a research project to develop methods to carry out fire safety design of welded steel tubular trusses at elevated temperatures due to fire exposure. It deals with three subjects: resistance of welded tubular joints at elevated temperatures, effects of large truss deflection in fire on member design and effects of localised heating. The objectives of the project are achieved through numerical finite element modelling at elevated temperatures using the commercial Finite Element software ABAQUS v6.10-1 (2011). Validation of the simulation model for joints is based on comparison against the test results of Nguyen et al. (2010) and Kurobane et al. (1986). Validation of the simulation model for trusses is through checking against the test results of Edwards (2004) and Liu et al. (2010).For welded tubular joints, extensive numerical simulations have been conducted on T-, Y-, X-, N- and non-overlapped K-joints subjected to brace axial compression or tension, considering a wide range of geometrical parameters. Uniform temperature distribution was assumed for both the chord and brace members. Results of the numerical simulations indicate for gap K- and N-joints (two brace members, one in tension and the other in compression) and for T-, Y- and X-joints with the brace member under axial tensile load (one brace member only, in tension), it is suitable to use the same ambient temperature calculation equation as in the CIDECT (2010) or EN 1993-1-8 (CEN, 2005a) design guides and simply replace the ambient temperature strength of steel with the elevated temperature value. However, for T-, Y- and X-joints under brace compression load (one brace member only, in compression), the effect of large chord deformation should be considered. Large chord deformation changes the chord geometry and invalidates the assumed yield line mechanism at ambient temperature. For approximation, the results of this research indicate that it is acceptable to modify the ambient temperature joint strength by a reduction factor for the elastic modulus of steel at elevated temperatures. In the current fire safety design method for steel truss, a member based approach is used. In this approach, the truss member forces are calculated at ambient temperature based on linear elastic analysis. These forces are then used to calculate the truss member limiting temperatures. An extensive parametric study has been carried out to investigate whether this method is appropriate. The parametric study encompasses different design parameters over a wide range of values, including truss type, joint type, truss span-to-depth ratio, critical member slenderness, applied load ratio, number of brace members, initial imperfection and thermal elongation. The results of this research show that due to a truss undergoing large displacements at elevated temperatures, some truss members (compression brace members near the truss centre) experience large increases in member forces. Therefore, using the ambient temperature member force, as in the current truss fire safety design method, may overestimate the truss member critical temperature by 100 °C. A method has been proposed to analytically calculate the increase in brace compressive force due to large truss deformation. In this method, the maximum truss displacement is assumed to be span/30. A comparison of the results calculated using the proposed method against the truss parametric study results has shown good agreement with the two sets of results, with the calculation results generally being slightly on the safe side. When different members of a truss are heated to different temperatures due to localised fire exposure, the brace members in compression experience increased compression due to restrained thermal expansion. To calculate the critical temperature of a brace member in a localised heated truss, it is necessary to consider this effect of restrained thermal expansion. It is also necessary to consider the beneficial effects of the adjacent members being heated, which tends to reduce the increase in compressive force in the critical member under consideration. Again, an extensive set of parametric studies have been conducted, for different load ratio, slenderness and axial restraint ratio. The results of this parametric study suggest that to calculate the critical temperature of a brace member, it is not necessary to consider the effects of the third or further adjacent members being heated. For the remainder of the heated members, this thesis has proposed a linear elastic, static analysis method at ambient temperature to calculate the additional compressive force (some negative, indicating tension) in the critical member caused by the heated members (including the critical member itself and the adjacent members). The additional compressive force is then used to calculate the limiting temperature of the critical member. For this purpose, the approximate analytical equation of Wang et al. (2010) has been demonstrated to be suitable.

[pt] Lâmpadas de fita de tungstênio de alta estabilidade não são mais adequadas como artefatos de comparação para termometria de radiação de alta temperatura, por conta de serem frágeis, terem um tamanho de alvo pequeno, serem limitadas com relação a faixa de temperatura e não serem corpos negros. Este estudo desenvolveu protótipos de artefatos de comparação de alto desempenho, os quais podem superar os problemas existentes ao usar tais lâmpadas em comparações da Escala Internacional de Temperatura de 1990 (EIT-90) entre Institutos Nacionais de Metrologia (INMs). Este trabalho demonstrou o conceito de utilização de pontos fixos de alta temperatura (PFATs) que tenham temperaturas desconhecidas e assim sejam adequados como artefatos de comparações às cegas. Quatro destes novos PFATs foram projetados, construídos, preenchidos e medidos no trabalho aqui descrito. Inicialmente Co-C foi escolhido, mas devido a problemas de robustez, a liga eutética base selecionada foi Ni-C. As células Ni-C foram dopadas em duas concentrações diferentes com elementos selecionados em uma tentativa bem sucedida de modificar temperatura de transição do eutético puro em alguns décimos de graus Celsius. As temperaturas de realização das células eutéticas determinadas no Inmetro foram comparadas com aquelas previstas por simulação termoquímica, usando o programa Thermo-Calc e bancos de dados de propriedades termoquímicas adequados. Além disso, elas foram utilizadas para realizar uma comparação às cegas com o National Physical Laboratory (NPL - UK), o qual não sabia a priori quais eram essas temperaturas. Resultados muito bons foram alcançados (concordância das escalas e estabilidade das células), demonstrando que as células dopadas são artefatos de comparação de alta temperatura bem adequados para termometria de radiação. / [en] High stability tungsten strip lamps are no longer suitable comparison artefacts for high temperature radiation thermometry, because they are fragile, have a small target size, are restricted in temperature range and are not blackbodies. This study developed proof-of-concept high performance comparison artefacts, which overcome the problems encountered when using such lamps in comparisons of the International Temperature Scale of 1990 (ITS90) among National Metrology Institutes (NMIs). This work demonstrated the concept of using high temperature fixed points (HTFPs) that have unknown temperatures and hence suitable as blind comparison artefacts. Four of these novel HTFPs were designed, constructed, filled and measured in the work described here. Initially Co-C was chosen but due to robustness issues, Ni-C was the selected the base eutectic alloy. The Ni-C cells were doped in two different concentrations with selected elements in a successful attempt to change the pure eutectic transition temperature by some tenths of degrees Celsius. The realization temperatures of eutectic cells determined at Inmetro were compared to the ones predicted by thermochemical simulation, using Thermo-Calc software and thermochemical property databases. In addition they were used to perform a blind comparison with the National Physical Laboratory (UK), which did not know beforehand what their temperatures were. Very good results were achieved (scale agreement and cell stability), demonstrating that doped cells are very suitable high temperature comparison artefacts for radiation thermometry.

La modélisation numérique des structures bois dans des conditions d’incendie nécessite la connaissance : de la variation des propriétés physiques du bois telles que la conductivité thermique, la chaleur spécifique et la densité en fonction de la température ; de la dégradation thermique du bois au cours des phases de séchage, de pyrolyse et de combustion. En particulier, nous nous sommes intéressés à l’étude du comportement thermomécanique du matériau bois. La loi thermique est décrite par l’équation de la chaleur. Le modèle choisi intègre les trois modes du transfert de chaleur : la conduction, le rayonnement et la convection. La loi mécanique est modélisée dans le cadre de la thermodynamique des processus irréversibles utilisant la notion des variables d’état. Elle tient compte du couplage entre le comportement élastique orthotrope, plastique anisotrope à écrouissage non linéaire isotrope et un endommagement isotrope. L’intégration numérique de la loi mécanique par un schéma implicite itératif combinant la technique du retour radial avec la réduction du nombre des équations est présentée. Le couplage thermomécanique est réalisé, selon l’approche réglementaire de l’Eurocode 5 relatif à la résistance au feu des structures en bois, en appliquant le facteur de réduction Kθ sur la résistance mécanique d’un résineux. Les aspects théoriques et les conditions aux limites associés au modèle thermomécanique sont abordés. L’identification des paramètres du modèle est réalisée sur des données expérimentales obtenues sur des tests réels d’incendie disponibles dans la littérature. À ce titre, plusieurs comparaisons avec différentes applications sont réalisées. Le modèle éléments finis reproduit avec précision la distribution du champ de température dans l’épaisseur des panneaux en bois, la formation du charbon ainsi que l’évolution de la résistance mécanique au cours de l’exposition au feu / Numerical modelling of timber structures in fire conditions requires the knowledge of the variation with temperature of the physical properties of the wood material (the thermal conductivity, the specific heat and the density) in order to take into account the thermal degradation of wood under high temperatures during the drying, pyrolysis and combustion phases, as well as the temperature profiles in the thickness of the surfaces exposed to fire. In particular, this work focusses on the thermomechanical behaviour of timber. The heat transfer analysis is described by the standard equations of heat conduction. It includes the three modes of heat transfer: conduction, radiation and convection. The structural response is modelled within the framework of thermodynamics of irreversible processes using the notion of state variables. It takes into account the coupling between the orthotropic elastic behaviour, the anisotropic plastic behaviour with isotropic nonlinear hardening, and isotropic damage. The numerical integration of the equilibrium equations is carried out with an iterative implicit scheme combining the technique of radial re- turn with the reduction of the number of equations. The thermomechanical coupling is carried out according to the approach recommended by Eurocode 5 for the fire resistance of timber structures by applying the reduction factor Kθ to the strength of a softwood. The theoretical aspects and boundary conditions associated with the thermomechanical model are also discussed. The parameters of the model are identified with experimental data obtained from actual fire tests available in the literature. Several comparative applications are carried out. The finite element model accurately reproduces the distribution of the temperature profile in the thickness of timber planks, the formation of the charred layer, and the evolution of the mechanical resistance during exposure to fire

Mg-Druckgusslegierungen sind aufgrund ihrer geringen Dichte potenzielle Leichtbauwerkstoffe. Ihre Festigkeitseigenschaften werden durch erhöhte Temperatur und die druckgussprozessbedingte Porosität maßgeblich beeinflusst. Zur Auslegung zyklisch belasteter Mg-Druckgussbauteile für eine begrenzte Betriebsdauer kann das Örtliche Konzept verwendet werden. Im Örtlichen Konzept nimmt das zyklische Werkstoffverhalten eine zentrale Rolle ein. Es umfasst das zyklische Verformungsverhalten und das zyklische Ermüdungsverhalten. Zur Beschreibung des zyklischen Werkstoffverhaltens werden die zyklische Spannungs-Dehnungs-Kurve für das Verformungsverhalten und die Dehnungswöhlerlinie für das Ermüdungsverhalten verwendet. Ziel der vorliegenden Arbeit ist es, die Einflüsse Temperatur und Porosität auf das zyklische Werkstoffverhalten der Mg-Druckgusslegierungen AZ91 und AM50 quantitativ zu erfassen. Dazu wird ein objektives Regressionsverfahren ermittelt, mit dem die zyklische Spannungs-Dehnungs-Kurve und die Dehnungs-Wöhler-Linie gemeinsam unter Einhaltung der Kompatibilitätsbedingungen aus den Daten einer Versuchsreihe regressiert werden können. Desweiteren wird eine Methodik entwickelt, mit der Ansätze zur quantitativen Erfassung von Einflüssen auf das zyklische Werkstoffverhalten aus Versuchsdaten abgeleitet werden können. Diese Methodik wird zur Untersuchung der Einflüsse Temperatur und Porosität auf das zyklische Werkstoffverhalten der Mg-Druckgusslegierungen AZ91 und AM50 angewendet. Die Untersuchungsergebnisse und deren Validierungen werden in dieser Arbeit vorgestellt. / Die-cast magnesium alloys are potential light-weight materials due to their low density. Their mechanical properties are significantly affected by elevated temperatures and by porosity, which die castings are especially prone to. The local strain approach can be used for dimensioning cyclically loaded magnesium die castings for a limited service life. The central role of this approach is assigned to the cyclic material behaviour. The cyclic material behaviour includes the cyclic deformation behaviour and the cyclic fatigue behaviour. It is characterized by the stress-strain curve for the cyclic deformation behaviour and by the strain-life curve for the cyclic fatigue behaviour. In the present work the aim is to describe the influence of elevated temperatures and of porosity on the cyclic material behaviour quantitatively. Therefore, a method is developed, which allows an objective and combined regression of the stress-strain curve and the strain-life curve for one test series. Furthermore, a methodology is developed, for deriving a formulation from experimental data to describe an arbitrary influence on the cyclic material behaviour quantitatively. This methodology is used to study the influences of elevated temperature and of porosity on the cyclic material behaviour of the die-cast magnesium alloys AZ91 and AM50. The results of the investigations and their validation are presented in this treatise.

In recent times, light gauge cold-formed steel sections have been used extensively in residential, industrial and commercial buildings as primary load bearing structural components. This is because cold-formed steel sections have a very high strength to weight ratio compared with thicker hot-rolled steel sections, and their manufacturing process is simple and cost-effective. However, these members are susceptible to various buckling modes including local and distortional buckling and their ultimate strength behaviour is governed by these buckling modes. Fire safety design of building structures has received greater attention in recent times due to continuing loss of properties and lives during fires. Hence, there is a need to fully evaluate the performance of light gauge cold-formed steel structures under fire conditions. Past fire research has focused heavily on heavier, hot-rolled steel members. The buckling behaviour of light gauge cold-formed steel members under fire conditions is not well understood. The buckling effects associated with thin steels are significant and have to be taken into account in fire safety design. Therefore, a research project based on extensive experimental and numerical studies was undertaken at the Queensland University of Technology to investigate the distortional buckling behaviour of light gauge cold-formed steel compression members under simulated fire conditions. As the first phase of this research program more than 115 tensile coupon tests of light gauge cold-formed steels including two steel grades and five thicknesses were conducted at elevated temperatures. Accurate mechanical properties including the yield strength, elasticity modulus and stress-strain curves were all determined at elevated temperatures since the deterioration of the mechanical properties is one of the major parameters in the structural design under fire conditions. An appropriate stress-strain model was also developed by considering the inelastic characteristics. The results obtained from the tensile coupon tests were then used to predict the ultimate strength of cold-formed steel compression members. In the second phase of this research more than 170 laboratory experiments were undertaken to investigate the distortional buckling behaviour of light gauge coldformed steel compression members at ambient and elevated temperatures. Two types of cross sections were selected with various thicknesses (nominal thicknesses are 0.6, 0.8, and 0.95 mm) and both low and high strength steels (G250 and G550 steels with minimum yield strengths of 250 and 550 MPa). The experiments were conducted at six different temperatures in the range of 20 to 800°C. A finite element model of the tested compression members was then developed and validated with the help of experimental results. The degradation of mechanical properties with increasing temperatures was included in finite element analyses. An extensive series of parametric analyses was undertaken using the validated finite element model to investigate the effect of all the influential parameters such as section geometry, steel thickness and grade, mechanical properties and temperature. The resulting large data base of ultimate loads of compression members subject to distortional buckling was then used to review the adequacy of the current design rules at ambient temperature. The current design rules were reasonably accurate in general, but in order to improve the accuracy further, this research has developed new design equations to determine the ultimate loads of compression members at ambient temperature. The developed equation was then simply modified by including the relevant mechanical properties at elevated temperatures. It was found that this simple modification based on reduced mechanical properties gave reasonable results, but not at higher temperatures. Therefore, they were further modified to obtain a more accurate design equation at elevated temperatures. The accuracy of new design rules was then verified by comparing their predictions with the results obtained from the parametric study. This thesis presents a description of the experimental and numerical studies undertaken in this research and the results including comparison with simply modified current design rules. It describes the laboratory experiments at ambient and elevated temperatures. It also describes the finite element models of cold-formed steel compression members developed in this research that included the appropriate mechanical properties, initial geometric imperfections and residual stresses. Finally, it presents the details of the new design equations proposed for the light gauge coldformed steel compression members subjected to distortional buckling effects at elevated temperatures.

Cold-formed steel members have been widely used in residential, industrial and commercial buildings as primary load bearing structural elements and non-load bearing structural elements (partitions) due to their advantages such as higher strength to weight ratio over the other structural materials such as hot-rolled steel, timber and concrete. Cold-formed steel members are often made from thin steel sheets and hence they are more susceptible to various buckling modes. Generally short columns are susceptible to local or distortional buckling while long columns to flexural or flexural-torsional buckling. Fire safety design of building structures is an essential requirement as fire events can cause loss of property and lives. Therefore it is essential to understand the fire performance of light gauge cold-formed steel structures under fire conditions. The buckling behaviour of cold-formed steel compression members under fire conditions is not well investigated yet and hence there is a lack of knowledge on the fire performance of cold-formed steel compression members. Current cold-formed steel design standards do not provide adequate design guidelines for the fire design of cold-formed steel compression members. Therefore a research project based on extensive experimental and numerical studies was undertaken at the Queensland University of Technology to investigate the buckling behaviour of light gauge cold-formed steel compression members under simulated fire conditions. As the first phase of this research, a detailed review was undertaken on the mechanical properties of light gauge cold-formed steels at elevated temperatures and the most reliable predictive models for mechanical properties and stress-strain models based on detailed experimental investigations were identified. Their accuracy was verified experimentally by carrying out a series of tensile coupon tests at ambient and elevated temperatures. As the second phase of this research, local buckling behaviour was investigated based on the experimental and numerical investigations at ambient and elevated temperatures. First a series of 91 local buckling tests was carried out at ambient and elevated temperatures on lipped and unlipped channels made of G250-0.95, G550-0.95, G250-1.95 and G450-1.90 cold-formed steels. Suitable finite element models were then developed to simulate the experimental conditions. These models were converted to ideal finite element models to undertake detailed parametric study. Finally all the ultimate load capacity results for local buckling were compared with the available design methods based on AS/NZS 4600, BS 5950 Part 5, Eurocode 3 Part 1.2 and the direct strength method (DSM), and suitable recommendations were made for the fire design of cold-formed steel compression members subject to local buckling. As the third phase of this research, flexural-torsional buckling behaviour was investigated experimentally and numerically. Two series of 39 flexural-torsional buckling tests were undertaken at ambient and elevated temperatures. The first series consisted 2800 mm long columns of G550-0.95, G250-1.95 and G450-1.90 cold-formed steel lipped channel columns while the second series contained 1800 mm long lipped channel columns of the same steel thickness and strength grades. All the experimental tests were simulated using a suitable finite element model, and the same model was used in a detailed parametric study following validation. Based on the comparison of results from the experimental and parametric studies with the available design methods, suitable design recommendations were made. This thesis presents a detailed description of the experimental and numerical studies undertaken on the mechanical properties and the local and flexural-torsional bucking behaviour of cold-formed steel compression member at ambient and elevated temperatures. It also describes the currently available ambient temperature design methods and their accuracy when used for fire design with appropriately reduced mechanical properties at elevated temperatures. Available fire design methods are also included and their accuracy in predicting the ultimate load capacity at elevated temperatures was investigated. This research has shown that the current ambient temperature design methods are capable of predicting the local and flexural-torsional buckling capacities of cold-formed steel compression members at elevated temperatures with the use of reduced mechanical properties. However, the elevated temperature design method in Eurocode 3 Part 1.2 is overly conservative and hence unsuitable, particularly in the case of flexural-torsional buckling at elevated temperatures.

Multiple step tests under cyclic strain control have been performed using cylindrical specimens of cast polycrystalline Inconel 738LC superalloy at 23, 700, 500, 800 and 900 °C in laboratory atmosphere to obtain cyclic stress-strain curves. During cyclic straining of specimen were obtained cyclic hardening-softening curves. Their progress changed with temperature and strain amplitude. Evaluated cyclic stress-strain curves are shifted to lower stresses with increasing temperature. Surface relief was observed in fatigued specimens under SEM and metalography under optic microscopy. Slip markings were studied on specimen surface fatigued at 700 °C .Stress-strain response is compared and discussed in relation to the surface observations - persistent slip markings.

Mg-Druckgusslegierungen sind aufgrund ihrer geringen Dichte potenzielle Leichtbauwerkstoffe. Ihre Festigkeitseigenschaften werden durch erhöhte Temperatur und die druckgussprozessbedingte Porosität maßgeblich beeinflusst. Zur Auslegung zyklisch belasteter Mg-Druckgussbauteile für eine begrenzte Betriebsdauer kann das Örtliche Konzept verwendet werden. Im Örtlichen Konzept nimmt das zyklische Werkstoffverhalten eine zentrale Rolle ein. Es umfasst das zyklische Verformungsverhalten und das zyklische Ermüdungsverhalten. Zur Beschreibung des zyklischen Werkstoffverhaltens werden die zyklische Spannungs-Dehnungs-Kurve für das Verformungsverhalten und die Dehnungswöhlerlinie für das Ermüdungsverhalten verwendet. Ziel der vorliegenden Arbeit ist es, die Einflüsse Temperatur und Porosität auf das zyklische Werkstoffverhalten der Mg-Druckgusslegierungen AZ91 und AM50 quantitativ zu erfassen. Dazu wird ein objektives Regressionsverfahren ermittelt, mit dem die zyklische Spannungs-Dehnungs-Kurve und die Dehnungs-Wöhler-Linie gemeinsam unter Einhaltung der Kompatibilitätsbedingungen aus den Daten einer Versuchsreihe regressiert werden können. Desweiteren wird eine Methodik entwickelt, mit der Ansätze zur quantitativen Erfassung von Einflüssen auf das zyklische Werkstoffverhalten aus Versuchsdaten abgeleitet werden können. Diese Methodik wird zur Untersuchung der Einflüsse Temperatur und Porosität auf das zyklische Werkstoffverhalten der Mg-Druckgusslegierungen AZ91 und AM50 angewendet. Die Untersuchungsergebnisse und deren Validierungen werden in dieser Arbeit vorgestellt. / Die-cast magnesium alloys are potential light-weight materials due to their low density. Their mechanical properties are significantly affected by elevated temperatures and by porosity, which die castings are especially prone to. The local strain approach can be used for dimensioning cyclically loaded magnesium die castings for a limited service life. The central role of this approach is assigned to the cyclic material behaviour. The cyclic material behaviour includes the cyclic deformation behaviour and the cyclic fatigue behaviour. It is characterized by the stress-strain curve for the cyclic deformation behaviour and by the strain-life curve for the cyclic fatigue behaviour. In the present work the aim is to describe the influence of elevated temperatures and of porosity on the cyclic material behaviour quantitatively. Therefore, a method is developed, which allows an objective and combined regression of the stress-strain curve and the strain-life curve for one test series. Furthermore, a methodology is developed, for deriving a formulation from experimental data to describe an arbitrary influence on the cyclic material behaviour quantitatively. This methodology is used to study the influences of elevated temperature and of porosity on the cyclic material behaviour of the die-cast magnesium alloys AZ91 and AM50. The results of the investigations and their validation are presented in this treatise.

Thin-walled cold-formed steel (CFS) has exhibited inherent structural and architectural advantages over other constructional materials, for example, high strength-to-weight ratio, ease of fabrication, economy in transportation and the flexibility of sectional profiles, which make CFS ideal for modern residential and industrial buildings. They have been increasingly used as purlins as the intermediate members in a roof system, or load-bearing components in low- and mid-rise buildings. However, using CFS members in building structures has been facing challenges due to the lack of knowledge to the fire performance of CFS at elevated temperatures and the lack of fire design guidelines. Among all available design specifications of CFS, EN1993-1-2 is the only one which provided design guidelines for CFS at elevated temperatures, which, however, is based on the same theory and material properties of hot-rolled steel. Since the material properties of CFS are found to be considerably different from those of hot-rolled steel, the applicability of hot-rolled steel design guidelines into CFS needs to be verified. Besides, the effect of non-uniform temperature distribution on the failure of CFS members is not properly addressed in literature and has not been specified in the existing design guidelines. Therefore, a better understanding of fire performance of CFS members is of great significance to further explore the potential application of CFS. Since CFS members are always with thin thickness (normally from 0.9 to 8 mm), open cross-section, and great flexural rigidity about one axis at the expense of low flexural rigidity about a perpendicular axis, the members are usually susceptible to various buckling modes which often govern the ultimate failure of CFS members. When CFS members are exposed to a fire, not only the reduced mechanical properties will influence the buckling capacity of CFS members, but also the thermal strains which can lead additional stresses in loaded members. The buckling behaviour of the member can be analysed based on uniformly reduced material properties when the member is unprotected or uniformly protected surrounded by a fire that the temperature distribution within the member is uniform. However if the temperature distribution in a member is not uniform, which usually happens in walls and/or roof panels when CFS members are protected by plaster boards and exposed to fire on one side, the analysis of the member becomes very complicated since the mechanical properties such as Young’s modulus and yield strength and thermal strains vary within the member. This project has the aim of providing better understanding of the buckling performance of CFS channel members under non-uniform temperatures. The primary objective is to investigate the fire performance of plasterboard protected CFS members exposed to fire on one side, in the aspects of pre-buckling stress distribution, elastic buckling behaviour and nonlinear failure models. Heat transfer analyses of one-side protected CFS members have been conducted firstly to investigate the temperature distributions within the cross-section, which have been applied to the analytical study for the prediction of flexural buckling loads of CFS columns at elevated temperatures. A simplified numerical method based on the second order elastic – plastic analysis has also been proposed for the calculation of the flexural buckling load of CFS columns under non-uniform temperature distributions. The effects of temperature distributions and stress-strain relationships on the flexure buckling of CFS columns are discussed. Afterwards a modified finite strip method combined with the classical Fourier series solutions have been presented to investigate the elastic buckling behaviour of CFS members at elevated temperatures, in which the effects of temperatures on both strain and mechanical properties have been considered. The variations of the elastic buckling loads/moments, buckling modes and slenderness of CFS columns/beams with increasing temperatures have been examined. The finite element method is also used to carry out the failure analysis of one-side protected beams at elevated temperatures. The effects of geometric imperfection, stress-strain relationships and temperature distributions on the ultimate moment capacities of CFS beams under uniform and non-uniform temperature distributions are examined. At the end the direct strength method based design methods have been discussed and corresponding recommendations for the designing of CFS beams at elevated temperatures are presented. This thesis has contributed to improve the knowledge of the buckling and failure behaviour of CFS members at elevated temperatures, and the essential data provided in the numerical studies has laid the foundation for further design-oriented studies.