Calculation rules of lightweight steel sections in fire situations

The main motivation of this research project on the fire behaviour of cold formed steel member is increasing the use of such components for both load-bearing and non load-bearing elements. The load-bearing elements are used in houses, low rise official or residential buildings as well as high storage constructions. Non load-bearing elements are widely used for partitions, for example with plasterboards, and often reach 10 or 15 metres in height in some constructions. Currently in the design of lightweight steel frames used in load-bearing and non load-bearing partitions, the contribution of non-structural items such as plasterboard and glazing to the overall stiffness of the structure is generally ignored in engineering codes. However, in fire it is known that the panels contribute significantly to the overall performance of the sub-frame such as through the development of membrane action. This contribution will depend upon the construction of the sub-frame - spacing, size and shape of the individual struts, the type and spacing of the connections, the material used for the panels and the level of protection provided to the steel members. Additionally the performance of the frame will depend upon whether it is designed to be load-bearing or non load-bearing at room temperature. All these aspects are not covered in existing fire design codes. In order to improve design efficiency and take advantage of economic benefits that may be accrued by considering the overall performance of sub-frames in fire, it is necessary to understand the fundamental engineering parameters that influence their behaviour and the interaction that is obtained by considering the frame as a whole rather than as individual components or elements. The objectives of this research programme are, therefore: 1) To increase the understanding in fire of the performance of lightweight steel frames to improve design efficiency, for example by quantifying the structural benefits that are obtained from including board or glazing elements. 2) To develop numerical analytical calculation methods that are capable of predicting the behaviour of lightweight steel frames under load and non-load bearing conditions taking into account infill panels. 3) To develop design rules that can be used in practice and that are harmonised across Europe for implementation into the European standards. In order to cover the field of application of cold formed lightweight steel members, as extensively as possible,, the research project was divided into the following parts: evaluation of the mechanical performance of cold formed steel at elevated temperatures, confirmation of the behaviour of cold formed steel members and assemblies, at room temperature conditions, assessment of the fire behaviour of fully engulfed lightweight steel studs, assessment of the fire behaviour of steel studs maintained by boards with fire on one side of the partition, verification of the fire behaviour of floors and wall-floor assemblies. For most of project parts, the research work was handled in the following way: analysis of existing knowledge, definition and performance of tests, analysis and numerical simulations with advanced calculation tools of test results, parametrical study, comparison with existing simple calculation methods and/or development of them. The above methodology allowed concentration of the experimental study on a number of key specimens.