Perforated Cold-Formed Steel Members in Compression. II: Design

The parametric study of the ultimate strength of perforated cold-formed steel columns is presented in a companion paper. The parameters include five cross-section types (i.e., C, stiffened C, Z, rack, and hat sections), five hole widths, four hole lengths, four hole spacings, three material properties, two magnitudes and various directions of geometric imperfections, and three buckling modes (i.e., L, D, and G) and all the possible interactions between them (i.e., LD, LG, DG, and LDG). Based on the extensive range of strength data obtained, four design methods based on the direct strength method (DSM) are evaluated, including the existing AS/NZS 4600 DSM (Australia Standard 2005), Design Option 4 by Moen and Schafer (2011), and two sets of proposed methods. All these methods are complemented by a reliability analysis deriving appropriate resistance factors. The proposed methods are based on Design Option 4 and include DG interaction. They only require the inputs of elastic local and distortional buckling loads based on gross section properties, which is a significant simplification compared to the methods based on net section properties. Additionally, Proposed Method 1 uses a uniform penalty factor to ensure the satisfaction of the overall resistance factor of 0.85, while Proposed Method 2 adopts a factor based on a regression analysis involving parameters such as the dimensions of holes and cross-sections. Proposed Method 2 outperforms all the other methods in terms of a reduced overall scatter in prediction and an increased overall reliability. This method can also be used for nonperforated columns with a better performance than the current AS/NZS 4600 DSM (Australia Standard 2005).