TESTS, MODELLING AND DESIGN OF UNSYMMETRICAL BACK-TO-BACK COLD-FORMED STEEL ANGLES UNDER COMPRESSION

Abstract

Built-up cold-formed steel (CFS) unsymmetrical angles are increasingly used in structures such as portal frames, roof trusses, and transmission towers. However, there are limited studies on CFS unequal back-to-back angle columns (BBUAC) with stiffeners. This paper presents the results of six experimental tests on intermediate BBUAC with intermittent screw fasteners. The findings include the deformed shapes at failure and the load-axial shortening behavior. Additionally, a nonlinear finite element (FE) model that accounts for both material and geometric nonlinearity was developed. The experimental results were used to validate this FE model. The paper presents a total of 166 new data points, which include six concentric compressive tests and 160 finite element analysis (FEA) results on the compressive strength of BBUAC. The effectiveness of the current design rules, based on the Direct Strength Method (DSM), was also evaluated. The evaluation revealed that the current DSM is unconservative. As a result, a modified DSM approach is proposed.