Behavior and design of sheathed cold-formed steel stud walls under compression.

摘要

Cold-formed steel may be used to frame the walls, floors, and roofs of modern buildings. The individual cold-formed steel members (studs) have sheathing attached to provide appropriate architectural enclosures. This sheathing also serves to brace the cold-formed steel studs under load. This thesis is dedicated to the study of sheathed cold-formed steel walls under axial loads.;Current design methods are highly developed regarding the design of isolated coldformed steel members such as columns and beams, but cold-formed steel wall studs that rely on sheathing for bracing are not fully addressed. A series of tests on single columns with sheathing, and full-scale walls with sheathing are completed herein and compared with previous design methods adopted by the American Iron and Steel Institute (AISI) Specification. The comparison shows that previous design methods lead to overly conservative strength prediction. This is particularly true for the case of dissimilar sheathing, e.g. oriented strand board on one face and gypsum board on the other face of the stud.;The sheathing supplies beneficial restraint to the wall studs and the stiffness of this sheathing-based restraint is characterized experimentally and analytically herein. The lateral bracing stiffness and resistance supplied by the fastener-sheathing combination that braces the stud is explored, taking into account typical design variables as well as the influence of humidity and construction flaws. For the first time, the lateral bracing stiffness is correctly divided into a local fastener and global diaphragm stiffness. While local stiffness considers the damage around the fastener connection, the diaphragm stiffness considers the shear stiffness of the whole sheathing.;Particular emphasis on the single-column and full-wall tests is placed on the behavior and the observed limit states given the different sheathing configurations. Demands on the fasteners that connect the sheathing to the studs are also explored analytically and numerically with finite element models of sheathed single columns and sheathed wall studs. A unique application of the Direct Strength Method of design is explored where the sheathing-based restraint is used explicitly in determination of the elastic buckling loads of the wall studs, and then these elastic buckling loads are utilized to determine the strength. An analytical solution for determining the buckling loads is provided, although it is involved and numerical methods are preferred. Good agreement is demonstrated for the new approach both in terms of strength and limit states prediction. The new approach is considered to be a suitable and reliable design method for adoption in the AISI Specification.