Cold-formed steel is ideal for lightweight construction applications because cold-forming allows for precise shapes and smooth finishes while creating a safe and efficient structural system. With a growing demand for lightweight, high-strength structural systems, CFS columns offer enhanced performance, especially in global and sectional buckling resistance. However, existing direct strength method provisions do not adequately account for the composite action and fastener effects in these configurations. Previous studies have shown that assuming either full or no interaction between component sections can lead to unsafe or overly conservative strength predictions, highlighting the need for a more accurate and calibrated design approach.
To ensure that design methods meet the minimum reliability standards set by North American and Australian specifications, researchers Mandana Abbasi, Kim J. R. Rasmussen, Mani Khezri, and Benjamin W. Schafer conducted a reliability assessment using parametric studies and proposed modifications to direct strength method equations. Their paper, “Design Rules for the Sectional Buckling of Built-Up Cold-Formed Steel Members in Compression,” presents a comprehensive evaluation and enhancement for the design of built-up CFS compression members. This research equips engineers with refined design tools, enabling more reliable and efficient structural designs. Learn more about using DSM to improve the accuracy of CFS buckling predictions by incorporating fastener effects in the Journal of Structural Engineering at https://ascelibrary.org/doi/10.1061/JSENDH.STENG-14404. The abstract is below.
Abstract
The paper investigates the design rules for built-up cold-formed steel columns, focusing on local and distortional (sectional) buckling. The accuracy of current design methods is studied through a comprehensive comparison with both experimental and numerical data. The results of these comparisons highlight the strengths and limitations of current approaches when applied to the sectional buckling of built-up cold-formed steel columns. A detailed reliability analysis is then undertaken to assess the performance of the current design methods. The results suggest that the direct strength method (DSM), combined with accurate elastic buckling stress calculations that include semirigid interconnections between sections, performs better in predicting the distortional buckling strength while still providing safe and efficient predictions of the local buckling strength. In addition, adjustments are proposed to enhance the accuracy of the current direct strength equations for the ultimate capacity predictions of built-up compression members to comply with the required level of reliability in the Australian and North American provisions while conserving the currently prescribed resistance factor. The proposed adjustments are established upon a rational modification of the parameters of the direct strength equations for local and distortional buckling capacities based on the relative number of restrained components in the built-up configuration undergoing the sectional buckling mode of interest and the fastener spacing relative to the associated critical buckling half-wavelength. The proposed modifications are reasonably accurate and robust for different built-up cross-section and fastener configurations.
See how this modified direct strength method calculation can enhance your structural design in the ASCE Library: https://ascelibrary.org/doi/10.1061/JSENDH.STENG-14404.
