Due to circumferential action of the spiral in a spirally reinforced column A. Capacity of column is decreased B. Ductility of column reduces C. Capacity of column is decreased but ductility of column increases D. Both the capacity of column and ductility of column increase

The correct answer is: D. Both the capacity of column and ductility of column increase.

The circumferential action of the spiral in a spirally reinforced column provides confinement to the concrete core, which increases the column’s capacity to resist axial loads. The spiral also helps to prevent the concrete from cracking and spalling, which increases the column’s ductility.

Option A is incorrect because the circumferential action of the spiral actually increases the column’s capacity.

Option B is incorrect because the circumferential action of the spiral actually increases the column’s ductility.

Option C is incorrect because the circumferential action of the spiral both increases the column’s capacity and ductility.