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ACI Plain Concrete Sm help

ACI Plain Concrete Sm help

ACI Plain Concrete Sm help

(OP)
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?

RE: ACI Plain Concrete Sm help

(OP)
thank you, but this pdf doesn't mention anything about Sm, just thermal issues with mass concrete.

RE: ACI Plain Concrete Sm help

I think it is just S = Ig / c of the gross section of the member.

RE: ACI Plain Concrete Sm help

(OP)
That's what I was thinking, ACI is unclear if they mean that though. Thanks for the confirmation JAE!

RE: ACI Plain Concrete Sm help

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.

RE: ACI Plain Concrete Sm help

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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