Cold-Formed-Steel Oval Hollow Sections under Axial Compression

Abstract

A test program was performed on cold-formed-steel oval hollow sections under axial compression. The test specimens were cold-rolled into oval hollow sections with flat web plates and semicircular flanges. The test program included a total of 28 column specimens that were separated into four series of different cross-sectional dimensions. Each series involved at least six specimens of different lengths to obtain a column curve. The columns were compressed between fixed ends. The overall geometric imperfections of the column specimens were measured prior to testing. The failure modes of the specimens included flexural buckling, local buckling, material yielding, and interaction between local and overall buckling. Material properties of each series at the flat and curved portions were determined from tensile coupon tests. The current design specifications for cold-formed-steel structures do not cover the design of oval hollow sections. Hence, certain assumptions on the calculation of effective width have been made in this study. The test strengths were compared with the design strengths predicted by the North American, Australian/New Zealand, and European specifications for cold-formed-steel structures. The test strengths were also compared with the design strengths predicted by the American Iron and Steel Institute Specification for automotive steel that includes design rules for local instability of sections with curved and straight elements. A reliability analysis was also performed. It is shown that the design strengths predicted by the three specifications are generally conservative.