Compression tests of fixed-ended and pin-ended cold-formed lipped channels

Abstract

The report presents an experimental investigation into the test strengths and the behaviour of cold-formed lipped channel columns compressed between fixed ends and pinned ends. It is well-known that local buckling of pin-ended channel columns induces overall bending of the section. However, this phenomenon does not occur in fixed-ended channel columns which remain straight after local buckling until overall buckling occurs. Consequently, local buckling has a fundamentally different effect on the behaviour of pin-ended and fixed-ended channel columns. A series of tests was performed on lipped channels brake-pressed from zinc-coated Grade G450 structural steel sheets. Two different cross-section geometries were tested at various lengths which involved pure local buckling, distortional buckling as well as overall flexural buckling and flexural-torsional buckling. The different effects of local buckling on the behaviour of fixed-ended and pin-ended channels are investigated by comparing strengths, load-shortening, load-deflection, load-end-rotation and load-end-moment curves, as well as longitudinal profiles of buckling deformations. Detailed measurements of geometric imperfections, material properties and residual stresses were conducted.