The plastic moment capacity M p is

SOLUTION

If the cross section of beam is subjected to yield stresses throughout the depth, it cannot take further loads. If any additional load is applied, then the beam rotates at that section. Since, the beam rotates due to moment, we call it plastic moment capacity and a plastic hinge is formed at that section. 

Plastic moment capacity is greater than the yield moment because in plastic stage all the fibres are yielded where as in other only outer fibre yields.

Also,

\({\rm{Shape\;Factor}},{\rm{\;SF}} = \frac{{{\rm{Plastic\;Moment}}}}{{{\rm{Yield\;Moment}}}}\)

Shape factor of every type cross-section is always greater than 1 i.e.

SF > 1

Plastic Moment > Yield Moment