Stiffness based design method for sheathed cold-formed steel members subjected to torsional buckling

The objective of this paper is to study the bracing effect of various sheathing boards in inhibiting the instability failure modes of cold-formed steel (CFS) studs in the wall panel construction. A development of accurate and robust sheathing braced design concepts for CFS wall panels will eliminate the need for additional steel bracing, thereby leading to efficient use of construction materials. The design method of American Iron and Steel Institute lacks in accurately predicting the design strength of the sheathed CFS wall panel. Therefore, the current investigation endeavors to fill the gap. A total of sixty-seven experiments were carried out with seven different sheathing board types and ten different CFS studs. The experiments were carried out using a newly devised test set-up that simulates the worst case failure mode of the sheathing board. The experimental results indicate that the strength, stiffness and failure modes of the sheathing boards vary depending on; (i) material properties and fiber composition of the sheathing boards; (ii) dimensions of the CFS stud. Based on the inferences (trend of sheathing stiffness and failure modes) from the test results, a new expression is formulated to determine the stiffness of the sheathing board on a function of the tensile modulus of the sheathing board and dimensions of the CFS stud. The validation study indicates that the new expression is accurate in terms of both statistical and design application.