Abstract

In steel construction the methods to produce structural members include hot rolling, forming and welding hollow section (HSS) and welding plates to form I's (WWF). Another method, which is less widely known but is growing in acceptance, is cold-forming from steel sheet or strip using roll-forming machines, press and bending brakes, or folding operations. These cold-form steel sections have their own design codes. The use of cold-formed structures in building constructions goes back to about the 1850s in both the United States and Great Britain but the formal design methods for these sections were developed only since 1940. Cold-formed sections add aspects to the design procedure which are neglected in codes for hot-rolled shapes, namely local and torsional buckling. The elements of a box or channel section formed from thin sheet may buckle locally, leading to collapse. To calculate the buckling stress the manufacturing process, makes the measurement of the width uncertain. Codes simply adopt the flat width. The objective of this study is to develop a more accurate method to predict the buckling stresses for two major kinds of cold-formed section, namely an open section (channel) and a closed section (box). A theory has been developed to model the elastic local buckling mode for box and channel sections. This is extended to predict the behavior of the section after buckling and up to the collapse. Comparisons are made with the results of the numeric analysis carried out using the finite element program ABAQUS, and with the code requirements.