A little off topic...
Is the new NCEES Structural Sample Questions & Solutions (NCPSE5) any different from the old one?
http://ppi2pass.com/ppi/PPIShop?ct=STRUCTU...0&pr=NCPSE5
Does it have all the horrible erratta errors the last one did?
I would only study the most basic of bridge design.
I wouldn't worry about anything harder than what is in the 6 min solutions books or the NCEES practice tests.
Z = Plastic Section Modulus (Steel is in plastic range - this means that the whole section is at yield stress)
S = Elastic Section Modulus (Steel is all in elastic range - that means it hasn't passed the yield point yet)