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ACI Plain Concrete Sm help

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dm3415

Structural
Joined
Sep 27, 2007
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Is anyone familiar with finding the "elastic section modulus" called Sm noted in ACI 318-05 in the plain concrete section, chapter 22? I can find no specific calculation for it; would I assume a regular S section modulus?
 
thank you, but this pdf doesn't mention anything about Sm, just thermal issues with mass concrete.
 
I think it is just S = Ig / c of the gross section of the member.

 
That's what I was thinking, ACI is unclear if they mean that though. Thanks for the confirmation JAE!
 
Wang and Salmon, 3rd Edition page 809 and page 830 in 4th edition cover design of plain and unreinforced concrete.

For the bending of plain concrete, the authors use 5 root f'c for modulus of rupture with a strength reduction factor of 0.65.

Section modulus is still bh^2/6 and I = bh^3/12.

So Phi Mn = phi*f*I/(h/2) where f = 5 root f'c

Compare Mu to phi Mn like you would normally do.
 
Actually, ACI 318-05 calls for a phi factor of 0.55 for plain concrete (for all types of members) in section 9.3.5.
 
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