Tests of fixed-ended cold-formed stainless steel built-up closed section columns

Abstract

An experimental investigation to examine the buckling behaviour of cold-formed stainless steel built-up section columns is presented in this paper. Stainless steel sheets of high-strength austenitic grade S35657 and duplex grade S22053 (equivalent to AISI 2205) were adopted to brake-press unlipped and lipped channel components, which were employed to assemble built-up closed section members using self-plugging rivets. A total of 26 fixed-ended column tests were conducted to examine two built-up closed sectional configurations consisting of two unlipped channels or one lipped and one unlipped channels, two nominal plate thicknesses of 1.5 and 2.0 mm, three nominal member lengths of 600, 1200 and 1800 mm, as well as fastener spacing varying from 100 to 400 mm and two different stainless steel types. Based upon the experimental results obtained from this study, the effects of stainless steel type, sectional configuration, member slenderness and fastener spacing on failure modes and loading capacities of the cold-formed stainless steel built-up closed section members experiencing axial compression were discussed. By evaluating against the ultimate loads obtained from the column tests, it was found that the design rules provided in the Chinese Standards and American Specification resulted in conservative strength predictions by averages of 14% and 19% on grade S35657 as well as 29% and 17% on grade S22053, respectively, for the fixed-ended cold-formed stainless steel built-up closed section columns.