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Doweling Rebar Into Existing Foundation For Addition

Discussion in 'Residential Foundation Codes' started by fj80, Oct 12, 2016.

  1. fj80

    fj80 Bronze Member

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    I'm add an addition to an existing house and need to provide rebar dowels from new foundation and footings into existing. Are there tables in the IRC 2012 that give a prescriptive method for doing this?
     
  2. JBI

    JBI Sawhorse

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    I don't believe there are, but not everything is 'prescriptive'. Some things still need to be designed...
    See if R404.1.3.3.7.8 helps. No table or figure, but a nice description of construction joint reinforcement.
     
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  3. Francis Vineyard

    Francis Vineyard Sawhorse

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    Correction: R404.1.2.3.7.8

    For further information reference ACI 318-11
     
  4. fj80

    fj80 Bronze Member

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    Thank you. Follow up questions: R404.1.2.3.7.8 has an exception that appears to say you don't need to provide construction joint reinforcement if you're using vertical wall reinforcement at no more than 24" spacing. This doesn't seem to make sense because how does vertical wall reinforcement help tie my new concrete wall to the existing?

    Is the bottom line this is an issue that must be designed because there's no prescriptive method?
     
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  5. JBI

    JBI Sawhorse

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    R404.1.2 is for masonry walls and never gets to a sub-section as long as you indicate in the 2012 IRC.
    R404.1.3 is for concrete walls and does include a sub-section as indicated in my prior post.
     
  6. Francis Vineyard

    Francis Vineyard Sawhorse

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    John, fj80 references 2012; clarify are you referencing 2015?

    My copy of the 2012;

    R404.1.1 Design of masonry foundation walls. Masonry foundation walls shall be designed and constructed in accordance with the provisions of this section or in accordance with the provisions of TMS 402/ACI 530/ASCE 5 or NCMA TR68-A.

    R404.1.2 Concrete foundation walls. Concrete foundation walls that support light-frame walls shall be designed and constructed in accordance with the provisions of this section, ACI 318, ACI 332 or PCA 100.

    R404.1.3 Design required. Concrete or masonry foundation walls shall be designed in accordance with accepted engineering practice when either of the following conditions exists:
    1. Walls are subject to hydrostatic pressure from groundwater.
    2. Walls supporting more than 48 inches of unbalanced backfill that do not have permanent lateral support at the top or bottom.
     
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  7. Francis Vineyard

    Francis Vineyard Sawhorse

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    Correct

    However there's not enough information to go on to require that a dowel attachment is necessary.
     
  8. my250r11

    my250r11 Sawhorse

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    IMO yes. Need engineer to figure the loads and decide how many, how deep, what kind, strength of epoxy, Etc.
     
  9. conarb

    conarb Sawhorse

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    In addition to that you need a Special Inspector to stand by and inspect the epoxy doweling, the residential code diverts to Chapt 17 of the IBC on this, AHJs will not stand by and wait.
     
  10. FLSTF01

    FLSTF01 Sawhorse

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    You don't specify the height, thickness, soil type or unbalanced fill amount, however there are some basic rules of thumb (if I dare say that). In standard residential construction with 8-foot walls, we typically see four #4 bars drilled in 10-12 inches, sticking out about 10-12 inches, spaced more or less equally. Drill a half inch hole, pound rebar in, no epoxy is typically used and most inspectors in this area will accept it.
     
  11. JBI

    JBI Sawhorse

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    Francis, I was also looking at the 2012 Commentary in the office...
     
  12. bhale7wv

    bhale7wv Sawhorse

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    The pins into the original foundation are for shear, not lateral movement.
    When butting up a new footing to a basement wall, the boss would have us simply knock a hole or two in the cinderblock about 6" round, stuff some ruble into the top of the block below the holes & allow the concrete to flow into the block & drop a piece of rebar in once the concrete level was half way up the hole.
     

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