Stability of Sheathed Cold-Formed Steel Studs under Axial Load and Bending

This research aims to identify and characterize the behavior of dissimilarly sheathed cold-formed steel (CFS) lipped channels (studs) under axial load and bending. These experiments are part of a larger effort to improve design methods and general understanding of CFS columns and their components, utilizing standard construction methods and sheathing configurations: Oriented Strand Board (OSB) and gypsum board. Previous work on sheathed studs and full-scale walls (Vieira, 2011) under axial compression alone demonstrated that sheathing on both sides of the member triggered a local buckling limit state and further restricted global and distortional modes. This was found to be true even for dissimilarly sheathed members, excepting walls and studs sheathed only on one side. In the tests conducted herein single CFS studs, sheathed with OSB or gypsum, or left bare (and any combination thereof on the two sides of the stud) are tested in axial compression and bending. Axial compression was applied to a pre-determined percentage of axial peak capacity (varying from 10% to 80% of the axial capacity of the stud) and then a horizontal load located at specimen mid-height was applied until failure. This configuration results in axial load, bending, and a direct torsion on the CFS stud. To stabilize the stud, tracks at the stud ends were clamped to the top and bottom of the testing rig to avoid liftoff during application of the horizontal load and to better simulate the response of full-walls, with multiple studs and wider sheathing. The immediate goal of the tests is to define the strength of similar and dissimilarly sheathed studs under combined loads. Sheathing type as well as configuration with respect to the loaded face was found to significantly effect the specimen response. Results are compared to nominal section strength. The combination experimental and analytical results will be utilized in full-scale CFS building experiments, modeling, and recommended changes to the AISI specification.

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