Experimental investigation of closed built-up sections using four cold-formed steel open sections under axial and eccentric loading

The light gauge steel structure (i.e., cold-formed steel framing) has been widely used in low-rise buildings for its ease of construction and high strength to weight ratio. However, this structural system is limited in member strength and stiffness and inhibits the flexibility of openings for doors and windows and also its use in mid-rise buildings and beyond. Innovation in cold-formed steel moment framing systems is needed. This study proposes a closed built-up section using four cold- formed steel open sections with a high load-bearing capacity that enables the development of high-performance cold-formed steel moment framing systems for mid-rise buildings and beyond. The closed section by combining four open cold-formed steel sections using fasteners can effectively enhance the local and distortional buckling load capacity of the sections under axial loading. Combining with specially designed intersections gusset plate this built-up section offers more potential configurations of beam-column moment connections for cold-formed steel structures. First, a heuristic optimization was performed based on the local and distortional buckling strength using the finite strip method. Second, a test program was developed to investigate the load-bearing capacity of this optimized closed section under axial and eccentric loading. The axial and eccentric loading tests of the built-up closed section column revealed the failure modes of the section under different loading conditions, axial and eccentric in the major-axis and weak-axis, and their load-carrying capacities. The study paved the groundwork for exploring high-performance cold-formed steel moment framing systems with this strong closed built-up section.This work was sponsored by the Natural Science Foundation of Jiangsu Province (BK20191268); and the Project of Central Government for Local Science and Technology Development of Tibetan Autonomous Region (XZ202201YD0032C)