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This paper develops a method, based on the Direct Strength Method (DSM) global buckling curve, to calculate the global buckling ultimate strength of cold-formed thin-walled (CF-TW) steel members under uniform and non-uniform elevated temperatures. The assessment is carried out by checking the DSM curve-based results with numerical simulation results using the general finite element software ABAQUS. The numerical model has been validated against a series of ambient temperature and fire tests on panels made of two different lipped channel sections tested to their ultimate load carrying capacities at ambient temperature or to their fire resistance at different load levels. The validated numerical model has been used to generate a database of numerical results of load carry capacity of CF-TW members with different uniform and non-uniform temperature distributions in the cross-sections under different boundary and loading conditions and with different dimensions. It is concluded that the DSM global buckling column curve is directly applicable for uniform temperature but a simple modification is required for non-uniform temperature distributions.

Cold-formed thin-walled steel sections are usually used as the load-bearing elements of wall panels in building construction. Such panels consist of channel steel sections with gypsum plasterboard layers attached to the flanges on the outside and interior insulation. This paper proposes a simple method to calculate temperature distributions in the steel section when the panel is exposed to fire from one side. This method calculates the average temperatures in the flanges of the steel section and assumes that the temperature in the web is linear. The proposed method is based on simple heat balance analysis for a few nodes representing the key components of the panel. The thermal resistance of these nodes is obtained from the weighted average of thermal resistances in an effective width of the panel within which heat transfer in the panel width direction is assumed to occur. The effective width of the panel for calculating the weighted average of thermal resistances can be taken as the steel section flange width plus 15% of the difference between 300 mm and the flange width of the steel section. Validity of the proposed method has been checked by comparison of the temperature results between the proposed 1-D modelling and 2-D ABAQUS Finite Element modelling for an extensive set of parametric and sensitivity studies covering different steel section dimensions (width, depth, thickness and lips), different spacing between steel section, number of gypsum layers (1 or 2) and different interior insulation properties. Further assessment of accuracy of the proposed temperature calculation method has been provided by comparing compressive resistance of the steel studs between using temperature profiles produced by 2-D ABAQUS Finite Element simulation and by using the proposed simplified method. Although the simplified method still requires a numerical procedure, it is extremely easy to implement to give designers of this structural system a much more efficient tool than using Finite Element simulations to calculate its fire resistance.

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