Flexural Buckling Curves of High-Strength, Wide-Flange Steel Columns

Abstract

Rolled shapes using structural steel with a specified yield strength, F_y, of 65 ksi or higher are considered an alternative solution to built-up shapes using conventional steel grades. However, major evidence exists that current design rules (e.g., AISC 360, Eurocode 3) are likely overly conservative for these higher-strength steels with F_y ≥ 65 ksi—particularly at yield strengths of 80 ksi and above when employed as structural steel columns—due in part to assumptions regarding residual stresses. In order to understand the extent of these conservative predictions and explore if alternative design provisions could be provided to engineers utilizing specific shapes and high-strength materials grade, this study presents comprehensive nonlinear finite element analyses of rolled W-shape columns made from ASTM A992 (F_y = 50 ksi) and A913 Grade 80 (F_y = 80 ksi) steels. The models incorporate validated multiaxial residual stress distributions, geometric imperfections, and nonlinear material behavior, and are benchmarked against experimental data.
Column flexural buckling curves are developed for a range of cross-sectional geometries and slenderness ratios and compared to predictions from AISC 360 and Eurocode 3 for both major and minor axis buckling. For A992 (F_y = 50 ksi), the AISC column curve overestimates the buckling strength for heavier sections and underestimates it for more slender or lightly built shapes, reflecting shape-dependent divergence. For A913 Grade 80 (F_y = 80 ksi), simulation results are generally close to AISC predictions, with a 5–14% increase in buckling strength observed, depending on the section geometry and slenderness. The findings generally support the use of AISC 360-22 but suggest refinement might be needed for heavier or high-strength rolled shapes in the inelastic buckling range. The results also highlight the potential need for shape- or grade-specific column curves. Future experimental validation will be essential to confirm these trends and guide potential updates to design standards.