Small Footings - Rebar Development Lengths
Small Footings - Rebar Development Lengths
(OP)
Hello all,
I was wondering if someone can give me some advice I've been wondering about for some time. I work in low-rise and mid-rise residential in a high seismic area and I'm sitting here staring at my design for a 18"X18"X12" (12" deep) shallow footing to support a very light deck. My question is in regard to the rebar and the development lengths associated with these shallow footings.
To allow the bars to develop, I prescribe that the contractors hook the bars. Am I reading into this correctly, or can the contractors just place the bars flat? Any suggestions to make these sort of designs more constructable?
Thanks,
R
I was wondering if someone can give me some advice I've been wondering about for some time. I work in low-rise and mid-rise residential in a high seismic area and I'm sitting here staring at my design for a 18"X18"X12" (12" deep) shallow footing to support a very light deck. My question is in regard to the rebar and the development lengths associated with these shallow footings.
To allow the bars to develop, I prescribe that the contractors hook the bars. Am I reading into this correctly, or can the contractors just place the bars flat? Any suggestions to make these sort of designs more constructable?
Thanks,
R






RE: Small Footings - Rebar Development Lengths
I know that the code calls for rebar in foundations of all high seismic areas, but omitting the steel here is really a no brainer. Usually, the vertical stub steel to a concrete column or plinth above can function as horizontal steel in the footing if the bars have a 6" or so bend at the end into the footing.
Mike McCann, PE, SE (WA)
RE: Small Footings - Rebar Development Lengths
If bending governs, I figure that the bars need to be hooked to have them develop adequately for tension?
Even if shear governs, I feel that I would still need to hook the bars to argue that the bending has been compensated for?
RE: Small Footings - Rebar Development Lengths
Mike McCann, PE, SE (WA)
RE: Small Footings - Rebar Development Lengths
1-1/2 cover each side leaves a 3x3 "square" to put rebar within.
So, you bend a 1/2 dia rebar into a square 3x3, right?
RE: Small Footings - Rebar Development Lengths
Mike McCann, PE, SE (WA)
RE: Small Footings - Rebar Development Lengths
A footing 18"x18"x12" deep doesn't need to be reinforced at all according to the Canadian code because the depth is greater than the overhang, even if the pedestal is 4" x 4". There used to be a section in ACI 318 dealing with plain concrete in footings, but I don't have a recent standard. Is it still included?
BA
RE: Small Footings - Rebar Development Lengths
I agree that in such a small footing, the reinforcement does nothing, but as standard practice, I cog (hook) all bottom bars.
RE: Small Footings - Rebar Development Lengths
Anyhow, to answer the OP's question, use small bars and provide more reinforcing than required for flexure so that you can justify a partial development length. In a footing so small, the reduced rebar length (no hooks) will likely offset the increase in steel area provided. And, of course, you'll accrue that constructibility improvement.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Small Footings - Rebar Development Lengths
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Small Footings - Rebar Development Lengths
RE: Small Footings - Rebar Development Lengths
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Small Footings - Rebar Development Lengths
BA
RE: Small Footings - Rebar Development Lengths
I've run across deep, moment resisting footings that technically also need to be designed STM per CSA. Almost intractable.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Small Footings - Rebar Development Lengths
Mike McCann, PE, SE (WA)