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Columns are categorized as short or long according to their slenderness ratios. Generally, the collapsing of short columns occur if their materials are exaggerated and the collapsing of long columns occur because of buckling that generates secondary moments caused by the P - D effect.

Columns are also categorized on the basis of the techniques to be reinforced into tied and spirally reinforced columns. Columns are generally reinforced with longitudinal and transverse reinforcement. If this transverse reinforcement remains in the shape of ties, the column is defined as “tied” whereas if the transverse reinforcement remains in the shape of helical hoops, the column is defined as “spirally reinforced”.

If the columns collapse, the building gets significantly damaged. To avoid this situation, the columns are designed by maintaining strict securities as compared to beams.

Columns are classified into three types on the basis of the technique they are reinforced:

Tied Columns

A tied column stands for a column in which the longitudinal reinforcement bars are affixed jointly with individual smaller diameter transverse bars (ties) which are arranged at some gaps along the column height. These ties are useful for retaining the longitudinal reinforcement bars in exact position throughout the construction and make sure the strength of these bars can withstand local buckling. The cross sections of such columns generally come in different shapes like square, rectangular, or circular. The lowest amount of four bars is utilized in rectangular and circular cross-sections.

Spirally-Reinforced Columns

In these types of columns, the longitudinal bars are placed in a circle enclosed with a tightly spanned continuous spiral. These columns generally come in the shape of circular or square. A lowest amount of six bars is utilized for longitudinal reinforcement.

Composite Columns

A composite column stands for a column that is developed with structural steel shapes or pipes encircled or filled with concrete having or not having longitudinal reinforcement.

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Designing Column