Axial Behavior of Cold‐Formed Steel Built‐Up I‐Section and Single C‐Section Wall Panels With Varied Sheathing Configurations: Experimental and Analytical Investigations

ABSTRACT This paper presents detailed experimental investigation of the axial behavior of cold‐formed steel (CFS) doubly‐symmetric channel (I‐section—referred as built‐up [BU]) and single channel (C‐section) wall panels with varying sheathing types and thicknesses. The experiments aim to enumerate ultimate axial strength, composite action, buckling interactions, failure pattern and effect of sheathing for BU section stud members. A total of 32 monotonic concentric axial compression tests were performed on 16 specimens (8 BU and 8 C‐section), with two samples tested for each specimen. The BU section vertical member consists of two separate CFS lipped C‐sections positioned back‐to‐back and coupled at the web using two screws at definite spacing along the length. The novelty is that, for the first time, an attempt is made to investigate and compare the axial behavior of BU and single C‐section wall panels using seven different sheathing board types namely, fiber cement boards (thickness of 8, 10, and 12 mm), heavy duty fiber cement boards (6, 9, and 12 mm), and calcium silicate boards (12 mm). Initial geometric imperfections are also measured on CFS sections using laser displacement sensor. Results show a large range of deformation behavior, with sheathed and unsheathed specimens of BU section undergoing distortional‐overall interaction and local‐flexural buckling modes and single C‐sections exhibiting local–global interactive buckling phenomena. Also, for the first time, the efficacies of four semi‐analytical methods based on a rational extension of the direct strength method (DSM) are compared. Alterations in the current DSM estimated and test results suggest the insufficiency of current AISI design specifications. Therefore, predicted results obtained using the suggested modified DSM methodology is within the adequate variation range (17% average for sheathed BU section specimens and 2% average for sheathed single lipped C‐section specimens) with the test results as the adopted methodology considers desired buckling interaction, the efficacy of the recommended design methodology is verified through reliability analysis.