Slenderness Ratio
Effective length ÷ radius of gyration; decides column buckling behaviour
The slenderness ratio λ = effective length (KL) ÷ least radius of gyration (r) is the dimensionless measure of a compression member's tendency to buckle rather than crush. A low λ means a short 'stocky' column failing by material yield; a high λ means a slender column failing by elastic (Euler) buckling at a load far below the squash load.
In steel design (IS 800 Cl. 7.1) the design compressive stress fcd drops sharply as λ rises, via the buckling-class curves (a, b, c, d). IS 800 caps λ at 180 for main members and 250 for bracing. In RCC (IS 456 Cl. 25.1.2) a column is 'short' if both lex/D and ley/b ≤ 12; beyond that it is 'slender' and additional moments from lateral deflection must be added per Cl. 39.7. Effective length K depends on end restraint (IS 456 Annex E, IS 800 Table 11).
- Steel column / strut capacity (IS 800 Cl. 7)
- Short vs slender RCC column classification (IS 456 Cl. 25)
- Bracing + truss-member design
- Scaffold + falsework standard design (IS 4014)
- Lacing + batten design of built-up columns