Local and Distortional Biaxial Bending Capacities of Cold-Formed Steel Storage Rack Uprights

Cold-formed steel storage rack-supported buildings, also referred to as clad racks, support both the building enclosure and the stored goods. Because of combined actions of wind loading and stored pallets, uprights undergo a combination of biaxial bending and compression. The focus of attention of this paper is only on pure biaxial bending capacity of the uprights. In cold-formed steel structures international specifications, a linear interaction equation is typically used to account for members subject to biaxial bending and may be inaccurate. In order to produce safe and economical design guidelines, this paper experimentally investigates the actual interactive relationship between bending of the uprights about the major and minor axes, for local and distortional buckling. Two types of regularly perforated and nonperforated storage rack uprights are investigated. Results show that a nonlinear interactive relationship governs the biaxial bending of the studied uprights, and the linear interaction equation in design specifications underestimates the biaxial bending capacity by up to 44 and 68% for local and distortional buckling, respectively. Also, the accuracy of the direct strength method (DSM) to directly predict the local and distortional buckling strengths of the uprights under biaxial bending is investigated. Results show that DSM equations provide better predictions but still underestimate the biaxial bending capacity by up to 27 and 36% for local and distortional buckling, respectively.