min footing thickness for continuous spread footings

[TBacon]

Does the ACI 318-08 15.7 minimum 6" depth of concrete over your reinforcing for footings apply to continuous spread footings? 15.1 clearly states that the requirement applies to isolated (pad) footings, but I'm wondering if it also applies to a typical continuous footings at, say, the perimeter foundation of a wood framed building.

Thanks

 

[KootK]

I've been assuming that it applies to strip footings. 10" feels like a good practical minimum footing thickness to me.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[wannabeSE]

The way I read ACI 318-08, section 15.7.1 applies to all footings.

 

[hokie66]

I would agree with the others, but in cases where plain concrete footings are adequate and permitted, a total depth of 8" is required (22.7.4). So if plain concrete can be used, and you just want to throw in some bars for good measure, you could put the bars at mid-depth.

 

[TehMightyEngineer]

Any reason you would want a footing less than 9" thick?

Maine EIT, Civil/Structural.

 

[KootK]

I agree with Hokie. In fact, most of my res strip footings do not have transverse rebar.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[hokie66]

TME,
I suggest the question should be "Why do you need a footing to be more than 8" deep?" We use 8" thick structural elements above ground, why is there anything wrong with an 8" deep x 16" wide strip footing under an 8" wall?

 

[manstrom]

8" is as thin as I would go on a strip (wall) footing.

 

[jike]

Smallest wall footing that we would use was 8" thick x 16" wide. We would provide (2) #4 longitudinal bars with #4 support bars (transverse) at 48" oc. I have seen too many times the longitudinal bars just set on bricks and roll off into the sand when the concrete is poured. The cost of the support bars is insignificant and is good insurance.

 

[oldestguy]

Hey designers: I'd bet, without detailed inspection, the majority of the residential wall footings are done without forms, meaning that the center may be 8 inches but the edges maybe a few inches. I've never seen one fail however.