ABSTRACT
The proposed design methodology consists of first carrying out a rational column buckling analysis of the corresponding elastic single Z-purlin with rotational end restraints under pure compression. To achieve this, the theory originally developed by Rasmussen & Trahair (2005) needed to be modified to account for the possibility of having different amounts of restraint at both ends of the column. The buckling load NE which is thus obtained is then used as the basis for calculating Nc (the pure compressive capacity of the purlin) and the moment amplification factor αm according to AS/NZS 4600 (2005). The factor αm is given by:
where N∗ is the design value of the applied axial load. It is noted that the AS/NZS 4600 (2005) specifications are concurrent with the AISI (2007) guidelines for the design of cold-formed steel (except for minor differences in notation).
