The diameter of longitudinal bars of a column should never be less than 12 mm.

Introduction:
The diameter of longitudinal bars in a column plays a crucial role in ensuring the structural integrity and strength of the column. It is essential to choose an appropriate diameter for the longitudinal bars to prevent any potential failure or damage to the column. In this context, the recommended minimum diameter for longitudinal bars is 12 mm.

Importance of Longitudinal Bars:
Longitudinal bars, also known as main reinforcement, are responsible for carrying the majority of the load in a concrete column. These bars are typically placed vertically in the column and are designed to resist bending and axial forces. The size and diameter of these bars directly impact the load-carrying capacity and overall stability of the column.

Factors Influencing Bar Diameter:
Several factors influence the choice of longitudinal bar diameter in a column, including:
1. Column Size: The size and dimensions of the column, such as height and cross-sectional area, affect the required diameter of the longitudinal bars. Larger columns generally require thicker bars to withstand higher loads.
2. Applied Loads: The magnitude and type of loads expected to be imposed on the column, such as dead loads, live loads, and seismic loads, influence the selection of bar diameter. Heavier loads necessitate larger diameter bars to ensure adequate strength and stiffness.
3. Reinforcement Ratio: The ratio of the total area of longitudinal bars to the cross-sectional area of the column, known as the reinforcement ratio, also affects the bar diameter. Higher reinforcement ratios may require larger diameter bars to meet the required strength and durability.
4. Concrete Strength: The compressive strength of the concrete used in the column construction is another important factor. Higher strength concrete may allow for the use of smaller diameter bars, while lower strength concrete may require larger diameter bars to compensate for the reduced strength of the material.

Minimum Diameter Requirement:
Considering all the factors mentioned above, it is generally recommended that the diameter of longitudinal bars in a column should never be less than 12 mm. This minimum diameter requirement ensures that the bars have sufficient strength and ductility to withstand the applied loads and prevent premature failure or deformation of the column.

Conclusion:
In summary, the diameter of longitudinal bars in a column is a critical design consideration. The minimum diameter requirement of 12 mm ensures that the bars can adequately resist the applied loads and provide the necessary strength and stability to the column. It is essential to adhere to this requirement to ensure the structural integrity and durability of the column.