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There are two main types of buckling, local and global buckling, in the elements under compressive for elements subjected to axial compression force.

Local Buckling

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

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TABLE B4.1a Width-to-Thickness Ratios: Compression Elements Members Subject to Axial Compression
Case	Element Description	Width-to-Thickness Ratio	Limiting Width-to-Thickness Ratio λr (nonslender/slender)	Examples
1	Flanges of rolled I-shaped sections, plates projecting from rolled I-shaped sections, outstanding legs of pairs of angles connected with continuous contact, flanges of channels, and flanges of tees	b/t	Mathinline body --uriencoded--$$ \normalsize 0.56\sqrt%7B\dfrac%7BE%7D%7BF_y%7D%7D $$
2	Flanges of built-up I-shaped sections and plates or angle legs projecting from built-up I-shaped sections	b/t	Mathinline body --uriencoded--$$ \normalsize 0.64\sqrt%7B\dfrac%7Bk_cE%7D%7BF_y%7D%7D $$
3	Legs of single angles, legs of double angles with separators, and all other unstiffened elements	b/t	Mathinline body --uriencoded--$$ \normalsize 0.45\sqrt%7B\dfrac%7BE%7D%7BF_y%7D%7D $$
4	Stems of tees	d/t	Mathinline body --uriencoded--$$ \normalsize 0.75\sqrt%7B\dfrac%7BE%7D%7BF_y%7D%7D $$
5	Webs of doubly symmetric rolled and built-up I-shaped sections and channels.	h/tw	Mathinline body --uriencoded--$$ \normalsize 1.49\sqrt%7B\dfrac%7BE%7D%7BF_y%7D%7D $$
6	Walls of rectangular HSS	b/t	Mathinline body --uriencoded--$$ \normalsize 1.40\sqrt%7B\dfrac%7BE%7D%7BF_y%7D%7D $$
7	Flange cover plates and diaphragm plates between lines of fasteners or welds	b/t	Mathinline body --uriencoded--$$ \normalsize 1.40\sqrt%7B\dfrac%7BE%7D%7BF_y%7D%7D $$
8	All other stiffened elements	b/t	Mathinline body --uriencoded--$$ \normalsize 1.49\sqrt%7B\dfrac%7BE%7D%7BF_y%7D%7D $$
9	Round HSS	D/t	Mathinline body --uriencoded--$$ \normalsize 0.11\sqrt%7B\dfrac%7BE%7D%7BF_y%7D%7D $$
*Case Cases 1, 2, 3, and 4 are Unstiffened Elements. Cases 5, 6, 7, 8, and 9 are Stiffened Elements.

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The limit state of flexural buckling is applicable for axially loaded columns with doubly symmetric sections, such as bars, HSS, and round HSS, and I-shapes, and singly symmetric sections, such as T- and U-shapes. Flexural buckling is the simplest type of buckling.

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• The compressive strength of the elements is determined according to the axial force acting from the section center of gravity. According to the regulation, the flexural buckling limit state is considered in all compression elements, regardless of cross-section properties.

• First of all, local buckling control should be done. The calculation is made to determine whether the elements are compact or non-compactnoncompact.

Torsional Buckling Limit State

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