Columns may be made of plain concrete if their unsupported lengths do not exceed their least lateral dimension

In RCC design, plain concrete columns are allowed only when the column is short and not subjected to significant bending.

According to standard design guidelines, a column can be made of plain concrete if its unsupported length does not exceed three times its least lateral dimension.

This limitation ensures that the column behaves primarily under axial compression and avoids buckling or instability.

If the length exceeds this limit, reinforcement becomes necessary to provide additional strength and stability.

Therefore, the correct condition is three times the least lateral dimension.