Cold-Formed Steel Gravity Walls with Bridging and/or Sheathing
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The objective of this report is describe experiments conducted on cold-formed steel walls under axial loading with a variety of different bracing conditions. Cold-formed steel wall systems are commonly braced using small bridging channels that run through the web of the studs (discrete bracing) as well as by sheathing that is attached directly to the stud flanges. Previous research has shown that sheathing, on its own, can be a highly effective means of bracing studs; however, sheathing is not always present during construction and in some cases, e.g. a sprinkler system saturating a gypsum board panel, may not provide adequate restraint. As a result, discrete (all-steel) bracing systems are sometimes favored. All-steel bracing systems under ultimate applied loads can be costly – particularly if brace force accumulation, and commensurate loss of stiffness, is properly accounted for in the design. To better understand the flow of forces in cold-formed steel walls with combinations of discrete and sheathing bracing a set of pilot experiments have been conducted. The experiments consider (a) whether or not the discrete bracing is properly resolved at its end, (b) whether or not gypsum sheathing is in place, in addition to the discrete bracing, and (c) sequence of loading, i.e., when the gypsum sheathing is installed. Forces in the discrete bracing are directly measured as is displacement of the studs under load. The resulting tests indicate that bridging only plays a secondary role in bracing steel studs once sheathing is installed. It is intended to use these results to develop improved engineering guidance on the use of combined, steel bridging plus sheathing, bracing conditions for walls.