Stability and design of built-up columns: effect of 2nd order shear forces

Current design standards for built-up steel members often overlook buckling effects, particularly when 2nd order shear forces in the lacing are substantial. This oversight can lead to overestimated member capacities and inaccurate force predictions. This study explores various nonlinear finite element (FE) models of laced built-up members fabricated from pairs of hot rolled C shaped sections connected by either double (X) or single (diagonal) flat lacing bars. It further investigates the influence of member properties and lacing configurations on the overall stability of the lacing system, explicitly considering axial forces both in compression and tension acting on the lacing elements. The developed FE models were carefully developed and rigorously validated against existing experimental data. A series of parametric studies was performed, and the numerical results were used to evaluate a newly proposed shear force design formula for laced built-up members with both double and single lacing systems. The assessment demonstrates that the proposed formulas provide more adaptable, accurate, and reliable predictions compared to those specified in Eurocode 3, Australian, and American design standards, and are also simpler than the current design rules. • This paper investigates numerical models for laced built-up members made of hot-rolled C-shaped sections with double and single lacing bars; • The study examines the impact of lacing arrangements and axial forces (compression and/or tension) on the overall stability of the lacing system; • Finite element models were carefully developed and validated against existing test data for accuracy; • A proposed shear force design equation for built-up members with double and single lacing systems is evaluated using numerical results; • The proposed equations provide more adaptable, precise, and consistent predictions compared to Eurocode 3, Australian Standards, and American Standards.