Why does column collapse?

Reinforced concrete column belongs to a compression member and it delivers the loads from structure toward the ground via foundations. On the basis of its height and lateral dimension, there exist three types of concrete columns. The ratio of height to minimum lateral dimension for long columns is over 12. When the height to minimum lateral dimension is under 3, it is recognized as a pedestal and if it lies among 3 and 12, it is known as a short column.

The load bearing capability and modes of failure concerning a reinforced concrete column is dependent on the slenderness ratio. Slenderness ratio refers to the ratio of the operative length Le and minimum lateral dimension of the column according to Indian and British Standards. But in accordance with American Concrete Institute Code of Practice, the slenderness ratio is known as the ratio of operative length of column to its radius of gyration, which has the similarity for structural steel design according to IS Code. Operative length of a column is based on its support conditions at ends.

The reinforced concrete columns can collapse due to three reasons which are dependent on the slenderness ratio of the column. The columns are supposed to be centrally loaded (without any eccentric loads).

Column Failure because of Pure Compression:

If reinforced concrete columns are loaded axially, there occur stresses for the reinforcement steel and concrete. If the loads are greater with regards to cross-sectional area of the column, the steel and concrete attain the yield stress and column collapses devoid of experiencing any lateral deformation. The concrete column is damaged and breaks down because of the material failure. To resolve the issue, the concrete column must contain adequate cross-sectional area, in order that the stress remains below the specified limit. This type of failure is usually found for pedestals whose height to least lateral dimension is below 3 and no bending occurs because of axial loads.

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Why does column collapse?