The steel section shown below is made from an elasto-perfectly-plastic material of strength Fy. It is an experimental structural shape of high strength steel rolled with extra edge-stiffeners to enhance local buckling strength. In this problem, only consider bending about the strong axis of the section.

(a) Calculate the yield moment (My ), plastic moment (Mp ), and shape factor for this section.

(b) Develop the P-M (axial force/bending moment) interaction curve for this steel section, expressed in terms of (M/Mp ) and (P/Pp ).

(c) Compare the resulting interaction curve with that for a corresponding W-shape beams (i.e., the same shape without the edge stiffeners), by plotting the resulting interaction diagram for both shapes.

(d) From the results in (c), could the interaction diagram for the case neglecting the stiffeners be used conservatively? Explain, based on fundamental principles, how this conclusion could have been predicted without any calculations.

(e) If that section had large residual stresses before any loads are applied to it, what would be their effect on the above findings?