Behavior of cold-formed steel wall stud assemblies subject to eccentric axial loads.

摘要

The overall behavior under axial loading of cold-formed steel wall stud assemblies is investigated. Wall stud assemblies consist of several wall studs acting as beam-columns, top and bottom tracks to restrain the ends of the studs and may include both diaphragm and discrete bracing.; Particular emphasis is placed on the study of the following: (1) loading eccentricity effects on axial strength, (2) the strengthening effects of wallboard sheathing, channel bridging and strap bracing, (3) effective lengths for buckling of braced and unbraced studs, and (4) the influence of widely-spaced rectangular perforations on strength and failure modes.; Experimental efforts include: (1) stub column tests to examine local buckling behavior, (2) individual long column testing to study the interaction of local and overall buckling, (3) cantilever connection tests to determine the stiffnesses and failure modes of typical stud-to-joist connections, (4) wallboard fastener connection tests to observe the behavior of connections between wallboard and studs using self-drilling screws, (5) flat-ended column testing to estimate loading eccentricities for wall studs and tracks bearing directly on concrete floors, and (6) wall stud assembly tests to observe the behavior of the overall system including the effects of bracing elements.; The test results are used to evaluate the current 1986 American Iron and Steel Institute specification for the design of cold-formed steel wall studs.; In general, the specification provides reasonable predictions of the observed behavior. However, a number of improvements to the specification are suggested.; The strong sensitivity of strength to loading eccentricity is highlighted. An analytical treatment of rectangular perforations using unstiffened elements on either side of the perforation is described and evaluated. Strap bracing and channel bridging are found to be effective systems for bracing against flexural and torsional-flexural buckling. Design recommendations for effective length factors for braced and unbraced wall studs are provided. Gypsum wallboard is observed to deform primarily locally at the fasteners and the current specification model which assumes shear diaphragm distortions does not appear to accurately describe the interaction between wall studs and the diaphragm. Future wall stud research to extend and validate this work is proposed.