Abstract
Recent developments in the practical utilisation of cold-formed sections in building construction have taken place on three related fronts. There have been significant developments in the technology which result in more complex shapes with a higher yield stress so that cold-formed sections represent a particularly high-tech form of constructional steelwork. Developments in technology would be of little consequence unless there were parallel developments in practical applications and this is illustrated by the continual increase in the market share of cold-formed sections. This, in turn, makes demands on design procedures and requires parallel development
in calculation models and design codes. In particular, sections have tended to become more highly stiffened and this necessitates a more sophisticated treatment of local buckling, distortional buckling and the interactions between them. The latest trend is to move from simplified design models to design procedures based on “whole section” analysis. In this paper, recent developments in technology and application are outlined and this is followed by more detailed consideration of the related design procedures.
Keywords: Beams; Buckling; Cold-formed; Columns; Distortion; Restrained; Steel; Thin-walled


1. Introduction
The market share of cold-formed structural steelwork continues to increase in the
developed world. The reasons for this include the improving technology of manufacture and corrosion protection which leads, in turn, to the increased competitiveness of the resulting product as well as new applications. This paper first reviews the technical developments and some of the resulting new applications. It is shown that as a result of current trends, cold-formed sections are becoming more slender and more highly stiffened and therefore more prone to local and distortional buckling. It then follows that there is a consequential demand for improved design procedures. These generally take the form of calculation models suitable for incorporation in design codes. The available approaches to the design of cold formed sections are reviewed in some detail and some possible improvements in design codes are anticipated.
2. Developments in cold-formed section technology


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