DESIGN OF COLUMNS:-- The design of walls and Columns is included because the columns and walls behave in a similar manner. A Column may be defined as an element used primarily to support axial compressive loads and with a height of atleast three times it's least lateral dimension. A compression member subjected to pure axially load rarely occurs in practice. All Columns are subjected to some moments which may be due to accidental eccentricity or due to end restraint imposed by monolithically placed beams or slabs. The strength of the column depends upon the strength of the materials , shape and size of the cross -section, length and the degree of positional and directional restraints at its ends .A Column may be classified based on the different criteria such as :- Shape of the cross -section, slenderness ratio ,type of loading and pattern of the lateral reinforcement. A Column may also be classified as short or long Column depending on its effective slenderness ratio
The ratio of effective Column length to least lateral dimensions is referred to as effective slenderness ratio.A short Column has a maximum slenderness ratio of 12 .It's design is based on the strength of the materials and the applied loads .A long Column has a slenderness ratio greater than 12 .However maximum slenderness ratio of a column should not exceed 60 .A long Column is designed to resist the applied loads plus additional BM induced due to its tendency to buckle. On the basis of loading a column may be classified as axially loaded Column, A Column subject to axial load and un-axial bending and a column subjected to axial load and bi-axial bending. A reinforced concrete Column can also be classified according to the manner in which the longitudinal bars are laterally supported ,that is, tied Column and spiral Column.
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