M Q Feng

Structural behaviour of cold-formed thin-walled short steel channel columns at elevated temperatures. Part 1: experiments

Cold-formed thin-walled steel structures are increasingly being used as primary load bearing members. However, there is a lack of study of their performance in fire. This paper presents a detailed description of an experimental study of the axial strength of cold-formed thin-walled channel sections under ambient and uniform high temperatures. The objectives of this study are two-fold: to gain an insight into the physical behaviour and failure modes of this type of structure and to provide some experimental results for detailed numerical studies. A total of 52 strength tests were carried out on short cold-formed lipped channels with and without service holes and unlipped channels at ambient and various elevated temperatures. From these experimental studies, it has been observed that the failure mode of two nominally identical columns can be different even though the failure loads are close. Depending on the thickness of a channel and the location of the service hole, perforation can have an important effect on the strength of the channel, irrespective of the temperature. The companion paper will describe the results of design calculations and numerical studies.

Structural behaviour of cold-formed thin-walled short steel channel columns at elevated temperatures. Part 2: Design calculations and numerical analysis

Abstract The companion paper has presented results of elevated temperature tests on 52 cold-formed thin-walled channels under compressive load. This paper presents the results of theoretical studies using a number of different calculation tools, these including simple design calculations based on modifying a few current design methods and a commercial finite element package ABAQUS. The design methods considered in this paper include the British standard BS5950 Part 5, Eurocode 3 Part 1.3 and the American Specification AISI. Modifications of the current design equations are made to enable them to include distortional buckling, the effects of service holes and elevated temperatures. To enable BS5950 Part 5 and Eurocode 3 Part 1.3 to predict the ultimate strength of thin-walled columns with a service hole, the AISI (1996) design method is introduced. To extend the capacity of these design methods to deal with distortional buckling failure mode, the method of Young, Kwon and Hancock for calculating distortional buckling capacity is introduced in these codes. Finally, the ambient temperature design methods are modified to take into account changes in the strength and stiffness of steel at elevated temperatures. From extensive comparisons between the results of tests, code predictions and numerical analyses, it may be concluded that by adopting the aforementioned modifications, the current code design methods can be easily modified to consider these advanced modes of behaviour. For finite element analyses, both geometrical and material non-linearities are taken into account. The high temperature stress–strain relationships of steel are determined according to Eurocode 3, Part 1.2 or Outinen et al.