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rebar dowel size and spacing

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  • rebar dowel size and spacing

    In a non-seismic area without expansive soil, what's the most stringent dowel size and spacing you've seen for where one residential slab meets another, such as a porch or garage slab meeting a house slab? Have you seen more than 30" long, #4 rebar @ 24" OC?

  • #2
    Re: rebar dowel size and spacing

    If you are asking about splice length, the rule of thumb is 30 bar diameters, so for a No. 4 bar it would be 15".

    Kris M

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    • #3
      Re: rebar dowel size and spacing

      No, these are simple dowels - no splicing necessary.

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      • #4
        Re: rebar dowel size and spacing

        Why would these slabs be structurally connected?

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        • #5
          Re: rebar dowel size and spacing

          How important is it that the slabs stay perfectly aligned?

          Are you using any steel or wire in the new slab? If I was going to all the trouble of drilling in dowels, I think I would tie a couple of pieces of #4 across the dowels to tie them together. The cost would be minimal but it would make the assembly significantly stronger. (Of course one of the engineers may now chime in and tell me I am all wet.)
          :-)

          Is the new slab going in over a filled area where the possibility of additional settling exists?

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          • #6
            Re: rebar dowel size and spacing

            Good questions, Sweep8 and elcalvo. I'm not sure I have answers for you other than "that's the way we've always done it", but that's not good enough for this forum.

            Rebar or WWM is in both slabs, and the subgrade is well-compacted. I think it's important that the garage slab stay aligned to the driveway slab, but at other locations, maybe some movement wouldn't hurt anything. Come to think of it, shouldn't unconditioned garage and porch slabs experience frost heave? Do you guys just let the abutting slabs float? How much movement can be expected?

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            • #7
              Re: rebar dowel size and spacing

              Originally posted by charles View Post
              Good questions, Sweep8 and elcalvo. I'm not sure I have answers for you other than "that's the way we've always done it", but that's not good enough for this forum.

              Rebar or WWM is in both slabs, and the subgrade is well-compacted. I think it's important that the garage slab stay aligned to the driveway slab, but at other locations, maybe some movement wouldn't hurt anything. Come to think of it, shouldn't unconditioned garage and porch slabs experience frost heave? Do you guys just let the abutting slabs float? How much movement can be expected?
              I always put a nice deep control joint where the garage slab meets the driveway apron at the door openings, and it always cracks in short order. I have never tied the apron to the slab.

              I always have had at least one step up from the garage slab into the house so I have never tied a garage slab into the foundation. I have used dowels in situations where I needed to extend a slab. In those cases I have gone as close as 18" on center and tied them to the mat.

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              • #8
                Re: rebar dowel size and spacing

                Down here in gator country my architect would typically prescribe: drill and epoxy 36" #5s 24" o.c. into an existing footer with a min. of 6" imbediment. That solution would be for a monolithic pour on base material compacted to a min. of 2500 psi however. Years ago my AHJ would not have required the epoxy. I wonder how much epoxy gets specified for room additions and such in siesmic locations?

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