Effect of irregular perforation patterns on axial load-deformation response of cold-formed steel columns in a hybrid frame-wall

Abstract

A hybrid cold-formed steel (CFS) load bearing frame-wall capable of supplying enhanced lateral load capacity is presented. The frame-wall features discrete CFS columns that resist gravitational loads. The CFS columns have irregular perforation patterns in the web to accommodate several layers of tension-only diagonal bracing installed in the plane of the hybrid frame-wall. The impact of said perforations on CFS column axial load-deformation response is studied with validated nonlinear finite element analysis and through comparisons with the axial response of CFS columns with standard perforation patterns. Irregular perforation patterns caused by one, two, and three layers of diagonal bracing are considered. The effect of boundary conditions, sheet metal thickness, imperfections, and bracing on irregularly perforated CFS column axial load-deformation response is quantified. Computed elastic buckling loads and axial capacities are compared with predicted values. The considered prediction frameworks result in average overpredictions of axial load capacity by 13 % for pin-supported columns and average underpredictions by 9 % for fixed-end columns. The hypothesis that an increase in the number of perforations along the length of the member results in a decrease in axial load capacity is found to be true for pin-supported columns that exhibited global flexural buckling and untrue for fixed-end columns and braced pinned columns that feature irregular perforation patterns. It is concluded that if the CFS columns in the hybrid frame-wall feature standard perforation sizes and perforation spacing is not smaller than column depth, the impact of irregular perforation patterns on axial load-deformation response and capacity is limited, regardless of the variation of perforation density along the height of the column. If perforation sizes are enlarged, reductions in axial load capacity become notable. Similarly, reductions in sheet metal thickness and increases in imperfections exacerbate the effect of irregular perforation patterns on CFS column axial load-deformation response and capacity.