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I'm trying to find a code reference for welded wire reinforcement in residential concrete slab foundations. I though it was 6" overlap of the sheets, but some sources are saying it's more. Does anyone know the specific overlap required?

Location is Georgia, United States.

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Short version: Yes, 6” is adequate.

Long version: (and I have a keen interest in this topic...so it will be long): Rebar is placed (installed) for TENSION. We design concrete beams and slabs to “fail” in tension so it fails with a crack, rather than designing it to fail in compression so it fails with an explosion.

Tension occurs due to 1) bending stress, or 2) temperature stress. (Some would say “curing stress” too, but that is not correct, because the concrete is shrinking and therefore the steel is in compression. )

1) Bending stress is taken with rebar, not mesh. Mesh is too small to account for much tensile stress.

2) Temperature stress (usually in slabs) is minor compared to bending stress and mesh can “help” absorb this stress. (Installing control joints is another way of relieving temperature stress.)

The most accepted testing agency to identify how concrete and reinforcing steel reacts is ACI American Concrete Institute and is referenced in ALL Codes. They recommend 30 to 40 bar diameter for steel in tension, depending on the grade of steel and the grade of concrete.

Therefore, your wire mesh (probably #6 wire) is 0.16” diameter x 30 = about 4.8”.

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    Given that nearly all USA reinforcing mesh is 6" squares, 4.8 would be rather absurd. 6 or 12, and tie the two sheets together well. – Ecnerwal Feb 10 '18 at 4:50
  • There do seem to be other spacings available, if not at home centers. On the other hand, ACI 315.99 enshrines both 8" minimum (deformed wire mesh) and cross wire spacing plus 2" (6" minimum) for plain wire mesh. Unless, that is, you have massive overkill on the steel (more than twice the minimum) where the overlaps can be as little as 2" (but then you'd have an engineer designing it to know how much, and you ask them for the splice requirement. Myself, I say everything else in doing concrete and what sits on it is expensive, steel is cheap, buy more #4 rebar and tie it across all your mesh, – Ecnerwal Feb 10 '18 at 5:27
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6x6 is 6" +2" lap = 8" total per CRSI Standards:

  • 12.19 - Splices of welded plain wire reinforcement in tension. Minimum length of lap for lap splices of welded plain wire reinforcement shall be in accordance with the following.
  • 12.19.1 - When area of reinforcement provided is less than twice that required by analysis at splice location, length of overlap measured between outermost cross wires of each reinforcement sheet shall be not less than one spacing of cross wires plus 2 in., nor less than 1.5ld, nor 6 in. ld shall be the development length for the specified yield strength fy in accordance with 12.8.
  • 12.19.2 - When area of reinforcement provided is at least twice that required by analysis at splice location, length of overlap measured between outermost cross wires of each reinforcement sheet shall be not less than 1.5ld, nor 2 in. ld shall be the development length for the specified yield strength fy in accordance with 12.8.

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