Need help of a Nomianl Moment Formula

[pob11646]

I am checking the concrete strength of my footing, and came across this formula for the nominal moment of a one-foot section of my footing:

Mn = 5 * (fc')^1/2 * S

S = section modulus

Could someone please verify the validity of this formula, and where is this formula stated, i.e. provide some references where it may be found, please.

Thanks.

 

[jike]

This is for unreinforced (plain) concrete. Refer to ACI 318-02 (22-2).

 

[pob11646]

Thank you so much, jike. That really helped, and now I can move on with the checking.