Elementary question, and I ought to know the answer, but I don’t.
Nor do I have a copy of the building code for my locale, or a copy of IRC-whatever.
Residential construction, two story house on full basement. Nominal thickness (8″) foundation walls, sitting on continuous spread footings.
The steel running lineally in those footings is often called “temperature steel,” because structurally, it is doing nothing.
How many bars of what size, does your local AHJ require? Foundation builders ’round here typically run a pair of #4s, just to keep busy and look somewhat professional. We ain’t got no inspection here, unlike many of you, where a pro will require a look-see when forms are prepped and footings are ready to pour.
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2 # 5
2 #5s for single story 3 for two story.
Three #5 for two stories atop the foundation?
Code source, please, if you have it?
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"A stripe is just as real as a dadgummed flower."
Gene Davis 1920-1985
Not a code item here but a design requirement. If the PE puts in on the plans, it has to be in the footing. And most do just to CTA (Cover Their ####).
The fear of soil subsidence (sink holes are a threat in Florida) has many overbuilding foundations.
In Florida you also tie the footer steel to the wall steel which gets tied to the tie beam steel on top of the wall making a concrete and steel matrix from top top bottom.
Yeah, exactly! Which makes for alot of steel and alot of labor! On my recent project there are 74 verticals which tie to the footer steel and bond beam steel. Something like $2k just in rebar for a 1500 sq ft building.
Minimum 2-4's, more likely 5's for the 8' walls.
But then you throw in the 8" walls and you have to add "L"s for the wall verts, Alternating hooks.
Every basement here is calculated as a retaining wall.
"The steel running lineally in those footings is often called "temperature steel," because structurally, it is doing nothing."
Can you elaborate on this? I'm not disagreeing at all.
Think of it. The aspect ratio of its cross section is not at all beam-like.
It has a continuous almost-uniform loading coming to it from the wall above. The undisturbed soil on which it bears provides a uniformly distributed reaction. No bending moment to resist.
The steel is there just for control of shrinkage. Why the term "temperature," I cannot say.
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"A stripe is just as real as a dadgummed flower."
Gene Davis 1920-1985
Edited 4/19/2009 7:43 am ET by Gene_Davis
The steel is there just for control of shrinkage.
The structural purpose of the steel reinforcement in footers is:
1. limit cracking if the ground under the footer compresses, subsides, erodes, or expands/contracts with moisture variation. The ground changes with moisture in many regions - typically we will see an inch or two of movement, and it's almost impossible to tell which "virgin, undisturbed soil" will move and which will be stable.
2. Limit cracking at the corners with normal expansion and contraction. Unfortunately, virtually no one properly treats the steel at the corners, resulting in cracked footer corners in many cases.
There was a good article in FHB about the failures caused by improperly placed and sized footer steel a while back. I think it is reprinted in the Foundations book, but I am not certain.
Edited 4/19/2009 6:50 pm ET by woodturner9
Just have your steel company (who you order the rebar from) design the rebar for you that's what I do.