The correct answer is: A. 0.5% and not more than 5% of cross-sectional area.
The minimum reinforcement ratio in columns is specified in IS 456:2000 as 0.005 times the gross cross-sectional area of the column. This means that the area of steel reinforcement must be at least 0.5% of the gross cross-sectional area of the column. The maximum reinforcement ratio is not specified in IS 456, but it is generally recommended that it should not exceed 5% of the gross cross-sectional area of the column.
The minimum reinforcement ratio is intended to ensure that the column has sufficient strength to resist the applied loads. The maximum reinforcement ratio is intended to limit the cracking of the concrete.
The reinforcement ratio is calculated by dividing the area of steel reinforcement by the gross cross-sectional area of the column. The area of steel reinforcement is calculated by multiplying the number of bars by the cross-sectional area of each bar. The gross cross-sectional area of the column is calculated by multiplying the width of the column by the depth of the column.
The reinforcement ratio is an important design parameter for columns. It is important to ensure that the reinforcement ratio is within the specified limits to ensure that the column has sufficient strength and does not crack excessively.