PEin2010
Well-known member
What is the difference between 'S' and 'Z' on the AISC tables?
Actually, calculating Z is way simpler than calculating S.Now calculating Z is ridiculously complex compared to S so most likely they won't ask you to calculate it (whereupon S = I/c which is pretty straightforward).
Interesting... I haven't had to calculate it often (usually RISA does the leg-work for me) and I guess i went the long route since from what i remember calculating it for an I-beam was no fun. It was probably the case of the book complicating a subject in an attempt to make it simpleActually, calculating Z is way simpler than calculating S.Now calculating Z is ridiculously complex compared to S so most likely they won't ask you to calculate it (whereupon S = I/c which is pretty straightforward).
Calculating S - steps
1. Identify location of centroid as a weighted average of component areas
2. Calculate Moment of Inertia about this centroidal axis - Use Parallel Axis Theorem
3. S = I/c
Calculating Z - steps
1. Identify the plastic neutral axis as the line that splits the AREA into two eual parts
2. Z = sum of the first moments of all component areas about the PNA
So what are we suppose to use in the NCEES exam.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)
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