Reinforcement in top and bottom of beam/slab

[nagatalluri]

Guys

I am checking the design for substation foundation. The designer came up with minimum reinforcement as 1.56 in2 (top/bottom). He is using # 8 bar top and bottom. f we sum the areas then it meets the requirement, if not it is half of the required. (#8 bar area 0.79in2 where as required is 1.56in2).

Is it it ok to sum the bar areas from top and bottom or the requirement have to be met individually.

Please let me know

Thanks
NT

 

[JAE]

If you'd like some brain damage - go through this previous thread which beat this horse dead:

thread507-251751

I'm assuming that you are referring to the requirement in ACI 318 section 10.5.4 where it indicates minimum reinforcement for mats and footings by referring back to chapter 7.

In my opinion, 10.5.4 is mandating that you provide minimum chapter 7 reinforcement on the tension side of any place where the mat or footing has tension.
So you cannot use half top and half bottom. Section 10.5.4 is a requirement for minimum flexural reinforcement (which is what 10.5 is all about). It is not minimum temp/shrinkage reinforcement.

For some dumb reason, ACI thought they'd save some print type by referring back to chapter 7 instead of just printing out the minimum in 10.5.4 directly.

Hopefully the new ACI 319-14 will remedy this.

Check out Eng-Tips Forum's Policies here:
faq731-376

 

[Lomarandil]

JAE, it still kicks the reader over to the one-way slabs section, but R7.6.1.1 confirms your conclusion.