The correct answer is A. 30.
A short column is a column that is not susceptible to buckling. Buckling is a failure mode in which a column bends and collapses under compression. The slenderness ratio of a column is a measure of its susceptibility to buckling. It is defined as the ratio of the column’s length to its least lateral dimension.
A short column is one with a slenderness ratio less than 30. This means that the column is short enough that it will not buckle under compression.
A long column is one with a slenderness ratio greater than 50. This means that the column is long enough that it is susceptible to buckling.
Columns with slenderness ratios between 30 and 50 are considered to be intermediate columns. These columns are not as susceptible to buckling as long columns, but they are not as stable as short columns.
The slenderness ratio of a column is an important factor in determining its design. The design of a column must take into account the slenderness ratio in order to ensure that the column is able to withstand the loads that it will be subjected to.