Tests of cold-formed channel columns

Abstract

The paper presents a series of tests on cold-formed plain and lipped channel columns-compressed between fixed and pinned ends. While it is well-known that local buckling of pin-ended channel columns induces overall bending, this phenomenon does not occur in fixed-ended channel columns which remain straight after local buckling and only bend when overall buckling occurs. These fundamentally different effects of local buckling on the behaviour of pin-ended and fixed-ended channel sections lead to inconsistencies in traditional design approaches, which account for full or partial rotational end restraint solely by using effective lengths. A series of tests was performed on four different geometries of cross-section fabricated by brake-pressing from high strength steel sheet. Tests were performed over a range of lengths such that the column curves could be obtained. Detailed measurements of local and overall geometric imperfections, material properties and residual stresses were conducted. The purpose of this paper is first to present and compare the test strengths with current Australian/New Zealand, American and European specifications for cold-formed steel structures and, second, to propose recommendations for the design of fixed-ended channel columns. It is shown that a fixed-ended channel column can be designed using an effective length of half of the column length and assuming the applied force acts at the centroid of the effective section.