Sheathed Cold-Formed Steel Studs under Axial and Lateral Load

Abstract

This research aims to identify and characterize the behavior of dissimilarly sheathed, load bearing, cold-formed steel studs under axial and lateral load. A series of tests on single studs, set in track, and sheathed with either oriented strand board, gypsum board, or combinations thereof are completed. The tests approximate the behavior of a sheathed stud within a larger wall. In each test, a predetermined level of axial load (or displacement) is introduced into the stud and lateral displacement (load) is then applied and increased until failure. This configuration results in axial load, bending, and (potentially) torsion on the stud. Observed failure modes for studs sheathed on only one face include torsion and/or fastener pull-through. For studs sheathed on both faces, failure modes include torsion, local buckling, fastener pull-through, and bearing (particularly for gypsum-sheathed studs). Analysis of the torsional response indicates the important role of the sheathing in limiting torsion and in determining the demands on the member and fastener. The observed member limit states compared favorably with the direct strength method of design even when direct torsion is not explicitly considered. New models for strength prediction in the connection limit states are explored. A model based on the torsional capacity of the fastener-sheathing system, limited by first failure in either pull-through or bearing, provides the best agreement with the observed connection limit states. Recommendations for design are provided.