NCEES Practice Exam Problem 528

Has anyone worked problem 528 of the most recent (copyright 2011) practice exam? It is asking for the allowable load based on the bending in an angle leg. I understand the bending based on the elastic analysis with Sx, but I' not finding the reference for the plastic analysis. I'm familiar with the plastic section modulus, Zx, for beam bending but have always used the values right out of the tables.

The solution is using 0.25*b*h^2 for the plastic section modulus. Is there a specific reference for this? Also, it states Mp<1.6My. Is there a specific reference for this as well? Thanks.

The solution for the plastic section modulus is based on the definition of Z itself.

since Z is calculated as the first moment of area about a Neutral Axis which divides the section into exactly half it is generally 0.25(b*d^2) compared to the elastic section modulus.

In this case , neutral axis = (0.375*.5) and so the half the area is (6*.375*.5)

Thus the P.S.M = (6*.375*.25)

and I guess you got the rest.

For your first question check AISC Edition 13 page 17-36 (table 17-27) first figure

For your second question check AISC Edition 13 page 16.1-54, Chapter F6.1

And it should be the same for AISC Edition 14, I just don't have it right now.

Thanks for the replies. I think I found the references I was needing for this problem while looking at steel bearing plates yesterday.