Question $4$: Determine the maximum load P that can be applied to the truss structure shown below. The truss members are made of steel with an allowable yield strength equal to $250$ MPa and elastic modulus of $E=200$GPa. Use a factor of safety against buckling of $2\mathrm{.}5$ and only consider buckling in the plane of the structure.

$($Remember that $I_x=I_y=\frac{r^4}{4}$ for a circular area$)$