The equivalent length is of a column of length L, having both the ends fixed, is A. 2L B. L C. $$\frac{{\text{L}}}{2}$$ D. $$\frac{{\text{L}}}{{\sqrt 2 }}$$

The correct answer is $\boxed{\frac{{\text{L}}}{{\sqrt 2 }}}$.

A column with both ends fixed is a simply supported column. The equivalent length of a simply supported column is given by the following formula:

$$\text{Le} = \frac{{\text{L}}}{{\sqrt 2 }}$$

where $\text{Le}$ is the equivalent length and $\text{L}$ is the actual length of the column.

The equivalent length is a measure of the stiffness of the column. A longer equivalent length means that the column is stiffer and will deflect less under load.

The other options are incorrect because they do not represent the equivalent length of a simply supported column.