Composed columns from cold-formed steel Z-profiles: Experiments and code-based predictions of the overall compression capacity

Built-up cold-formed steel members are tested in compression. The main objective behind the experiments is to determine the overall compression capacity of double-Z columns, which are often used in the Belgian engineering practice. Eight full-scale tests on 4.45 m long columns are performed and out-of plane displacements and strains at six locations per member are recorded. The effect of initial imperfections is evaluated based on the measured longitudinal strains at mid-height. An attempt to relate the obtained ultimate capacity to prediction methods, based on the European standard for steel structures [1,2], is presented. The assumptions made in the analytical prediction and the gaps within the cited standard are explained and discussed. Certain aspects of the behaviour of such members cannot be represented in an Eurocode-base prediction, due to the restricted scope of [1,2]. A reference is made to North American Specification for the design of cold-formed steel structural members [3] as well, where a slightly better design methodology is available. Amendments to EN 1993-1-3:2006 are proposed and a design approach, based on the direct strength method is presented.