The correct answer is: A. Two times.
Plain concrete columns are not allowed to have an unsupported length greater than twice their least lateral dimension. This is because plain concrete is not as strong as reinforced concrete, and it is more susceptible to buckling. Buckling is a type of failure that occurs when a column is subjected to a load that is perpendicular to its long axis. The load causes the column to bend, and if the load is too great, the column will buckle and collapse.
The unsupported length of a column is the length of the column between two points of support. The least lateral dimension of a column is the smallest dimension of the column’s cross-section.
The following is a brief explanation of each option:
- Option A: Two times. This is the correct answer.
- Option B: Three times. This is not the correct answer. The unsupported length of a column is not allowed to be greater than twice its least lateral dimension.
- Option C: Four times. This is not the correct answer. The unsupported length of a column is not allowed to be greater than twice its least lateral dimension.
- Option D: Five times. This is not the correct answer. The unsupported length of a column is not allowed to be greater than twice its least lateral dimension.