Calculate and draw $($on the same graph$)$ the momentcurvature $(M-)$ curves for both cross$-$sections shown at right. Use a spreadsheet program such as Excel and use enough points to fully capture the shapes of the curves. Identify the following points $($and label with coordinates$)$: $($a$)$ cracking, $($b$)$ yielding $($if it occurs$)$ and $($c$)$ ultimate. Use gross$-$section properties to plot the curve for values of $M$ less than $M_{CR}.$

$f_c^{\text{'}}=30$MPa,${}_c^{\text{'}}=-0\mathrm{.}002,f_y=400$MPa,$N=0$

$E_s=200,000$MPa,$E_{CT}=5500\sqrt[\phantom{2}]{f_c^{\text{'}}}$MPa