Combined Axial and Bending Load Tests of Fully-Sheathed Cold-Formed Steel Wall Assemblies

Authors: NAHB Research Center Inc.    

The purpose of this test program was to investigate the structural capacity and performance of fully-sheathed load bearing walls of cold-formed steel framing. The configuration of the walls tested was limited to 4 foot by 8 foot wall panels sheathed with 2-inch gypsum wallboard (GWB) and 7/16-inch oriented strandboard (OSB) panels assembled in accordance with the Prescriptive Method for Residential Cold-Formed Steel Framing (Prescriptive Method). Currently, the allowable capacities of wall assemblies are calculated in accordance with the Specification for the Design of Cold-Formed Steel Structural Members (AISI Design Specification) based on the simplified beam-column approach. Each wall stud member is designed as an independent element, neglecting potential composite action and load sharing that occurs between the sheathing and the studs. This simplified design method underestimates the bending and compression capacities of the actual sheathed wall assembly resulting in a less than optimum design.

The goal of this research was to identify the degree of load carrying increase provided by OSB and gypsum panel sheathed wall assemblies relative to predicted capacities using the AISI Design Specifications. With significant strength increase, the additional cost of the exterior sheathing will be offset by the savings of using thinner more economical light-gauge steel studs for wall framing.

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