Studies on Cold-Formed Steel Stud Panels with Gypsum Sheathing Subjected to Out-of-Plane Bending

An experimental investigation on gypsum sheathed cold-formed steel (CFS) panels with different sheathing configurations was conducted under four-point bending (out-of-plane). The purpose of the study was to investigate the bracing effect of sheathing versus the slenderness of the CFS studs. To accomplish this objective, a total of 24 experiments using sheathed and unsheathed configurations were tested. The parameters studied include five different CFS slendernesses, two different sheathing thicknesses, and two different fastener spacings. The sheathed CFS panels were fabricated with two identical sheathings (gypsum boards) on both sides of the panel. The maximum fastener spacing was chosen based on the specification for gypsum panel fabrication by the Gypsum Association (GA). A comparison of the experimental results of the unsheathed specimens indicates the conservative nature of the American Iron and Steel Institute (AISI) design prediction equation for members with high slenderness. To further validate the experimental observation, geometric and material nonlinear finite-element studies were performed for unsheathed specimens. The design predictions of the tested CFS panels (sheathed) were calculated by considering the lateral, vertical, and rotational sheathing restraints as per the AISI’s research report. Two different composite actions (full and partial) based on the vertical sheathing restraint between the CFS studs and sheathings were carried out and incorporated in the design predictor equations. The test results indicate that the CFS studs with lower resistance to both lateral torsional buckling (LTB) ($f_{cre}\ll f_y$) and local buckling ($f_{crl}\ll f_y$) can be effectively braced by gypsum boards to achieve significant improvement in flexural strength with no major failure in the sheathing. A maximum of 81% increase in design flexural strength can be achieved by including the effect of bracing provided by sheathing with the adequate fastener spacing. Further, the maximum fastener spacing limitations were compared based on the results from the experimental study and fastener demand check available in the AISI report. In addition, reliability studies on the limited experimental results carried out indicate that the design guidelines available in the AISI report for sheathing braced CFS structural members can be used with a higher degree of confidence. For more clarity, a simple design example on the sheathed CFS panel has been carried out based on the AISI design method.