ROTATIONAL RESTRAINT OF DISTORTIONAL BUCKLING IN COLD-FORMED STEEL FRAMING SYSTEMS

Abstract: A series of cantilever tests on joist-sheathing assemblies were conducted to determine the rotational restraint that sheathing provides to the compression flange of a cold-formed steel floor joist in bending. This rotational restraint, characterized by the stiffness, kφ, can partially or fully retard distortional buckling. Tests were conducted for different joist thicknesses, depths, and flange widths, two fastener types, and plywood, oriented strand board (OSB), and gypsum board sheathing. The tests show that (1) variability in plywood sheathed specimens is due to the plywood, not the connection stiffness, (2) variability in OSB specimens is low, but primarily due to the connection stiffness, not the OSB, (3) gypsum board connection stiffness is high and consistent; but strength is low and variable, (4) joist thickness is the most important variable for determining connection stiffness, far more important than joist depth, joist flange width, or fastener size. A new design method is proposed for adoption