$13$ For a $8m$ tall column $($pin ended in a braced structure$)$ that supports an un$-$factored dead load of

$400kN$ and un$-$factored live load of $300kN.$ Column's dimensions: $500mm**500mm,f^{\text{'}}c=28$

MPa,$fy=420$MPa. The bending moment diagram for the column is shown below.

Consider the following;

$B_{dns}=0\mathrm{.}5$

Find only, the critical moment $(M_c)$ and load $(P_u)$ to be used in the design of this column. Don't use

the sheets of interaction diagrams.