Design of Built‐up Nested Cold‐formed Steel Channel Compression Members

Recently, the use of built‐up cold‐formed steel (CFS) members in the form of nested channel (NC) compression members is becoming more popular in CFS construction. For NC compression members, the current CFS design standards have been shown to be inadequate, provide over‐conservative predictions, and include some cumbersome design rules relating to maximum allowable screw spacing and end fastener groups. New design guidelines have been proposed by some recent research studies, however, they are based on different assumptions and provide varying capacity predictions. This study has investigated (1) the design guidelines in the current design standards and past research studies, and (2) the effects of screw spacing as well as end fastener groups on the compression behaviour and capacity of NC members. It included a series of compression tests on short, intermediate and slender single channel and NC members, followed by developing validated finite element models and undertaking parametric studies. The results show that: (1) the compression capacity of NC members can be greater than twice that of their individual members, (2) the design rules on the maximum allowable screw spacing and end fastener groups are over‐conservative, and are mostly unnecessary, (3) the design rules in the current standards and past research studies are not suitable for predicting the compression capacities of the investigated NC members, and (4) proposed design guidelines based on the Direct Strength Method in the current CFS design standards can provide reliable predictions for the compression capacities of NC members.