Center for Cold-Formed Steel Structures Library


INTRODUCTION Cold-formed steel wall studs generally are I, Z or channel shaped with or without stiffening lips, and with webs perpendicular to the plane of the wall. Because of their configuration and dimensions, these sections are quite unstable by themselves. However, the stability and, hence, load-carrying capacity of such studs are increased substantially once they are connected to the wallboard material. The main function of the wallboard is that of enclosure, but it serves also as a bracing system for the studs. Gypsum board, vegetable fiberboard, tempered board or plywood are commonly used wallboard materials. Such boards are connected to one or both sides of the studs (see Fig. 1) by means of self-drilling screws or other fasteners to provide an economical and quickly erected system for interior and exterior walls. The objective of the research reported here was to obtain an analytical formulation of the steel stud performance considering the bracing action of the wallboard which is usually referred to as diaphragm bracing and to obtain a design tool using this formulation. Only concentric loading was considered in this phase of the research. The bracing action of the wallboard is due both to its shear rigidity which restrains the displacement of the stud in the plane of the wallboard, and the resistance it offers to the twisting of the stud at the connectors. However, since the connector spacing is small compared to the length of the stud, a uniformly-distributed restraining medium is assumed in formulating the behavior. The parameters pertaining to the wallboard diaphragm are best determined experimentally. This is due to the fact that these parameters are influenced not only by the properties of the wallboard, but also to a significant degree by the local conditions at the connection between the stud and the wallboard. Parameters pertaining to the diaphragm are shear rigidity, shear deformation at failure, rotational restraint and rotation angle at failure. Shear rigidity represents the resistance of the wallboard material and the connections to shear deformations in the plane of the wallboard. Shear deformation at failure as well as shear rigidity are found using procedures outlined in Ref. 1. Rotational restraint and and rotation angle at failure are both determined as described in Ref. 12. Analytical determinations of the bracing effects due to the shear rigidity of steel diaphragms have been studied previously by Larson (9), Pincus (11), Luttrell (10), Errera (2,6,7), Apparao (1,2) as well as several other researchers. Errera has obtained formulations (1, 6) and design recommendations for diaphragm braced doubly symmetric I-Sections. In the research reported here an analytical formulation of the problem was obtained in a general form (12) using, the total potential energy of the stud and wallboard assembly. For this purpose expressions derived in Ref. 6 for doubly-symmetric sections had to be extended to singly-symmetric sections (such as channel and lipped channel sections) and to point symmetric sections (such as Z-sections with or without stiffening lips) which are commonly used for wall studs.


Civil, Architectural and Environmental Engineering


American Iron and Steel Institute

Research Center/Lab(s)

Wei-Wen Yu Center for Cold-Formed Steel Structures



Publication Date


Document Version

Final Version

Document Type

Report - Technical

File Type