Behaviour of tubular steel members under cyclic axial loading

This paper examines the cyclic performance of axially loaded tubular members used as bracing elements to provide lateral seismic resistance in steel framed structures. An experimental study into the response of members with square and rectangular hollow sections, made from cold-formed steel, is described. Three cross-sectional geometries were employed to represent a range of local and overall slenderness. Fifteen specimens, with normalised slendernesses between 0.4 and 3.2, were tested under cyclic axial displacements of increasing amplitude. In addition, twenty-one short specimens were tested under displacement-controlled monotonic tension loading, focusing primarily on the relationship between the tensile resistance of the material and that of the cross-section. Based on the results obtained in both sets of tests, and with due consideration of existing design provisions, the paper assesses the influence of section and member properties on the structural parameters that are most important for seismic design. These include the tensile capacity, initial and post-buckling compressive resistance, ductility capacity, energy dissipation, and mid-length lateral deformations of bracing members.