Local Buckling in Steel Design

Local buckling is the instability occurring in slender plate elements of steel members, such as flanges or webs, under compressive stresses before the entire member buckles. This phenomenon reduces the load-carrying capacity and serviceability of steel sections by causing premature deformation. The critical buckling stress for a plate strip is expressed as $\displaystyle f_{cr} = \frac{k \pi^2 E}{12(1-\nu^2)} \left( \frac{t}{b} \right)^2$, where is the buckling coefficient based on edge support conditions, is Young's modulus, the Poisson's ratio, plate thickness, and plate width. The local slenderness ratio classifies elements as slender, non-slender, or compact, influencing design criteria. Local buckling limits the effective width of plate elements, reducing the cross-sectional area actively resisting load. Structural steel design codes specify width-to-thickness limits to prevent or permit controlled local buckling with reduced strength. Neglecting local buckling may lead to unsafe, uneconomical designs. Proper understanding supports compliance with standards such as AISC and Eurocode and aids in selecting appropriate cross-section shapes and thicknesses balancing economy and safety.