What is the expression for crippling load for a column of length L, with one end fixed and other end free?

A

$$P = \pi^2 \frac {EI}{4L^2}$$

B

$$P = \pi^2 \frac {EI}{L^2}$$

C

$$P = 2 \pi^2 \frac {EI}{L}$$

D

$$4 \pi^2 \frac {EI}{L^2}$$