Transverse shear stiffness of bolted cold-formed steel storage rack upright frames with channel bracing members

Abstract

Accurately evaluating the transverse shear stiffness of cold-formed steel storage rack upright frames is crucial to calculate the frame elastic buckling load, perform earthquake design and serviceability checks. This is especially essential for high-bay racks, which are subjected to large second-order effects, and racks supporting the building enclosure, which are exposed to transverse wind loads. The shear behaviour of these frames is poorly understood and experimental testing is usually required to measure their stiffness. Previous studies have shown that Finite Element Analyses (FEA), solely using beam elements, fail to reproduce experimental test results and may overestimate the transverse shear stiffness by a factor up to 25. In this paper, a commercially used upright frame, with either bolted lip-to-lip or back-to-back channel section bracing members, has been modelled using shell elements. The model is verified against available experimental data and found to accurately predict the experimental shear stiffness with an average error of 7%. Based on the verified FE model, the factors contributing to the frame shear deformation are quantified. The different frame deformations imposed by the test set-ups in the European (EN15512) and Australian (AS4084) standards are both considered. The effects of the bracing lay-out, the bolt bending, local deformations of the uprights and bracing members at the connections on the performance of the upright frames are quantified and discussed.