(a) Show, from first principles, that the fully plastic moment Mp, of a mild steel beam of rectangular cross-section is 50% greater than the elastic moment, Me, which develops when the beam reaches its limit of elasticity.
(b) An I-section, 250 mm deep and 125 mm wide, is made of mild steel. The thickness of the web and the flanges are 12 mm and 20 mm, respectively. Find the ratio of the fully plastic moment and the elastic limit moment for the section.