Q$2(24\%).$ A reinforced concrete column is being analyzed.

$($a$)$ Find the following state points: $1.$ pure bending, $2.$ tension$-$controlled limit$,3.$ compression$-$controlled limit$,$ and $4.$ pure compression limit$.(10\%)$ You can use the Excel spreadsheet provided.

$($b$)$ Draw the interaction diagram. $(7\%)$

$($c$)$ If the column is subjected to the factored axial force $(P_u)=-800kN$ and the factored moment $(M_u)=80kN*m.$ Is it safe or not? $(7\%)$