Seismic modeling and behavior of hollow structural section columns with initial imperfections

This article investigates the impact of initial imperfections incurred during the cold-bending rolling process on the seismic behavior of Hollow Structural Sections (HSS) columns. To achieve this objective, the distribution of residual stresses and geometric imperfections was measured for a set of cold-formed HSS members with varying global and local slenderness ratios. A parametric analysis was conducted to examine the effect of different imperfections on the seismic capacity using validated finite element models. The results showed that the local geometric imperfections of most STKR490 sections exceeded the permitted variations in the specification, and there was a negative correlation between bending residual stress and the local slenderness ratio. Moreover, the influence of global geometric imperfections and residual stresses was minimal, inducing a <5% difference in strength and nearly no change in ductility of HSS columns. Conversely, the negative effect of local geometric imperfections increased with the increasing local slenderness ratio and reduced the strength by 5% and 22% for sections with ratios of 13 and 38, respectively. Based on the seismic performance expected in various provisions, modeling the local geometric imperfections is required to reflect the cyclic degradation for HSS columns disqualified as highly ductile members per AISC 341-22.