ACI Plain Concrete Sm help

[dm3415]

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?

 

[csd72]

look at this link (you my need to go to the main page to register):

http://www.gostructural.com/userfiles/file/pdhse1106.pdf

 

[dm3415]

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

 

[JAE]

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

 

[dm3415]

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

 

[minorchord2000]

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.

 

[Lion06]

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.