Experimental Investigation and Design Methodology of Built-Up I-Section Cold-Formed Steel Wall Panels with Sheathing under Axial Loading

The objective of this paper is to investigate the behavior of 16 cold-formed steel (CFS) wall panels consisting of 10 panels with a built-up I (BI)-section stud and six panels with a single-lipped C-section stud under compression. Limited studies are available in the literature on the axial performance of sheathed BI-section studded CFS wall panels. The novelty of the study is that for the first time, an investigation is conducted on axial performance of full-scale BI-section studded CFS wall panels with magnesium-oxide board sheathings. A comparison is also presented between the ultimate axial compressive strengths of BI-section studded wall panels and single-lipped C-section studded wall panels. Different sheathing configurations have been adopted in the study by varying the layers of sheathing on either side. Failure modes and ultimate axial compressive strength of all the tested specimens are compared and discussed in detail. Also, for the first time, efficacy of three direct strength methods (DSMs) have been verified against the experimental tests on sheathed BI-section studded CFS wall panels present in the literature database as well as tests conducted by the authors in the present study. Three DSM approaches include current DSM (cDSM) in the North American specifications and two other modified DSM (mDSM) approaches present in the literature. In all the approaches, the sheathing was assumed as continuous elastic supports attached to the C-section. Elastic buckling analysis was performed to evaluate the elastic buckling loads. Further, DSM design formulas were adopted to transform the elastic buckling loads to estimate the nominal axial compressive strength of sheathed CFS wall panel. Differences in the cDSM-predicted and experimental test results imply the inadequacy of current design rules. Due to the clear evidence obtained in the test, local-distortional and distortional-global interactive buckling modes cause substantial ultimate compressive strength erosion in sheathed CFS BI-section columns. Therefore, results obtained using the recommended mDSM approach are within the acceptable variation range with the experimental results because the adopted method takes into account distortional–overall buckling interaction. Structural designers and researchers will have a readily available tool to implement for evaluating the axial compressive strength of such members.