Influence of Geometric Properties and Axial Load Ratio on the Rotation Capacity of Cold-Formed Steel Square Hollow Sections

Cold-formed Hollow Structural Sections (HSS) play a crucial role in structural applications due to their effective strength-to-weight ratio as well as their torsional stiffness. However, both the first and second generations of the European seismic codes provide limited guidelines for the assessment of the ductility and plastic rotation capacity of HSS members. Analytical equations were recently proposed by the authors to predict both the cyclic rotation capacity and the overstrength of cold-formed HSS beams and columns at significant damage and near-collapse limit states. These equations were derived for members made of S355 steel subjected to low values of axial loads, i.e. for axial load ratios not higher than 0.3. As a preliminary step for the proposal of new predictive equations referred to members characterised by different steel grades and axial load ratios larger than 0.3, the correlation between the chord rotation capacity at the Significant Damage limit state and the Near Collapse limit state and some geometric parameters is here investigated. The data collected from the parametric analyses in previous research will be expanded with experimental data from various authors.