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Local buckling occurs when some part or parts of the cross-section of a column bending member are so slender that they buckle locally in compression. However, the flexural strength corresponding to any buckling mode cannot be developed if the cross-section element is so thin that local buckling occurs.

The measure of this susceptibility is the width-thickness ratio of each cross-sectional element.

Limit values ​​for the classification of cross-sections for the local buckling boundary condition are given in AISC 360-16 B.4 and Table B4.1a and b 1b for cross-sections under compressive force.

For design members for flexure, sections are classified as compact, noncompact, or slender-element sections.

Width-to-thickness ratio, λ

If λ ≤ λ_p, the element is compact,
If λ_p < λ ≤ λ_p, the element is noncompact,
If λ > λ_r, the element is slender.

TABLE B4.1b Width-to-Thickness Ratios: Compression Elements Members Subject to Flexure
Case	Element Description	Width-to Thickness Ratio	Limiting Width-to-Thickness Ratio		Examples
			λp (compact/ noncompact)	λr (noncompact/ slender)
10	Flanges of rolled I-shaped sections, channels, and tees	b/t	Mathinline body --uriencoded--$$ \normalsize 0.38\sqrt%7B\dfrac%7BE%7D%7BF_y%7D%7D $$	Mathinline body --uriencoded--$$ \normalsize 1.0\sqrt%7B\dfrac%7BE%7D%7BF_y%7D%7D $$
11	Flanges of doubly and singly symmetric I-shaped built-up sections	b/t	Mathinline body --uriencoded--$$ \normalsize 0.38\sqrt%7B\dfrac%7BE%7D%7BF_y%7D%7D $$	Mathinline body --uriencoded--$$ \normalsize 0.95\sqrt%7B\dfrac%7Bk_cE%7D%7BF_L%7D%7D $$
12	Legs of single angles	b/t	Mathinline body --uriencoded--$$ \normalsize 0.54\sqrt%7B\dfrac%7BE%7D%7BF_y%7D%7D $$	Mathinline body --uriencoded--$$ \normalsize 0.91\sqrt%7B\dfrac%7BE%7D%7BF_y%7D%7D $$
13	Flanges of all I-shaped sections and channels in flexure about the minor axis	b/t	Mathinline body --uriencoded--$$ \normalsize 0.38\sqrt%7B\dfrac%7BE%7D%7BF_y%7D%7D $$	Mathinline body --uriencoded--$$ \normalsize 1.0\sqrt%7B\dfrac%7BE%7D%7BF_y%7D%7D $$
14	Stems of tees	d/t	Mathinline body --uriencoded--$$ \normalsize 0.84\sqrt%7B\dfrac%7BE%7D%7BF_y%7D%7D $$	Mathinline body --uriencoded--$$ \normalsize 1.52\sqrt%7B\dfrac%7BE%7D%7BF_y%7D%7D $$
15	Webs of doubly symmetric I- shaped sections and channels	h/tw	Mathinline body --uriencoded--$$ \normalsize 3.76\sqrt%7B\dfrac%7BE%7D%7BF_y%7D%7D $$	Mathinline body --uriencoded--$$ \normalsize 5.70\sqrt%7B\dfrac%7BE%7D%7BF_y%7D%7D $$	Image Added
16	Webs of singly symmetric I-shaped sections	hc/tw	Mathinline body --uriencoded--$$ \normalsize \frac %7B\frac%7Bh_c%7D%7Bh_p%7D \sqrt%7B\frac%7BE%7D%7BF_y%7D%7D%7D %7B \Big ( 0.54 \frac%7BM_p%7D%7BM_y%7D -0.09 \Big)%5e2 %7D $$	Mathinline body --uriencoded--$$ \normalsize 5.70\sqrt%7B\dfrac%7BE%7D%7BF_y%7D%7D $$	Image Added
17	Flanges of rectangular HSS	b/t	Mathinline body --uriencoded--$$ \normalsize 1.12\sqrt%7B\dfrac%7BE%7D%7BF_y%7D%7D $$	Mathinline body --uriencoded--$$ \normalsize 1.4\sqrt%7B\dfrac%7BE%7D%7BF_y%7D%7D $$	Image Added
19	Webs of rectangular HSS and box sections	h/t	Mathinline body --uriencoded--$$ \normalsize 2.42\sqrt%7B\dfrac%7BE%7D%7BF_y%7D%7D $$	Mathinline body --uriencoded--$$ \normalsize 5.70\sqrt%7B\dfrac%7BE%7D%7BF_y%7D%7D $$	Image Added
20	Round HSS	D/t	Mathinline body --uriencoded--$$ \normalsize 0.07 \dfrac%7BE%7D%7BF_y%7D $$	Mathinline body --uriencoded--$$ \normalsize 0.31 \dfrac%7BE%7D%7BF_y%7D $$	Image Added
21	Flanges of box sections	b/t	Mathinline body --uriencoded--$$ \normalsize 1.12\sqrt%7B\dfrac%7BE%7D%7BF_y%7D%7D $$	Mathinline body --uriencoded--$$ \normalsize 1.49\sqrt%7B\dfrac%7BE%7D%7BF_y%7D%7D $$	Image Added