A Column is said to be slender if its cross-sectional dimensions are small compared with its length. Therefore a “slender column” has a ratio of width vs. length of around 1:100. An excessively slender column would have a width/height ratio of 1:200 or greater, per the AISC — American Institute of Structural Steel Const.
The slender column is one having smaller cross sectional dimensions as compared to its length. In a structure, a slender column has less strength as compared to short column with the same sectional area. Due to this the slender column carries lesser load as compared to the short column. Slender columns are those members whose ultimate load carrying capacities are affected by the slenderness effect, which produces additional bending stresses or instability of columns. Therefore, evaluation of a slender column involves consideration of the column length in addition to its cross section. The column having ratio of effective length to its list lateral dimension exceed or equal to 12 according to IS 456-2000 is treated as slender column (Shinde & Patil, 2015).
The slender column is developed in multistoried structure due to increasing ground floor height for functional purpose or architectural purpose. On the other hand, the modern trend is towards taller and slender structures.
Slender columns resist lower axial loads than short columns having the same cross-section. Therefore, the slenderness effect must be considered in design, over and above the sectional capacity considerations incorporated in the interaction diagrams. The significance of slenderness effect is expressed through slenderness ratio.
The degree of slenderness in a column is expressed in terms of “slenderness ratio,” defined below: Slenderness Ratio:
Where, ul is unsupported column length; k is effective length factor reflecting the end restraint and lateral bracing conditions of a column; and r is the radius of gyration, reflecting the size and shape of a column cross-section. (Saatcioglu, n.d.)