Question $1($CLO$3)$: Column analysis and classification

A built$-$up steel box section has been designed to resist load in pure axial compression $($i$.$e$.,$ moment $=0).$ The section is comprised of several $12mm$ thick $300W$ steel plates $)=(300$MPa welded together as shown in Figure $1.$

a$)$ By considering the requirements of $S16-19Cl.11,$ determine whether the section satisfies the maximum width$-$to$-$thickness limits for a member subjected to axial compression.

b$)$ If the column is to be pinned at both ends and has a length, $L$ of $9\mathrm{.}1$ metres, determine the factored compression resistance, $Cr.$ Assume $n=2\mathrm{.}24$ and note that you will need to determine the critical section properties in your analysis. Recall that $r^2=\frac{\text{I}}{A}.$

Figure $1.$ Built$-$up steel column section $($Question $1)$