Two-Way Slab-Order or Rebar Placement
Two-Way Slab-Order or Rebar Placement
(OP)
I am working on small footprint 2 way slab 30" thick, surrounded by walls around the entire perimeter, essentially making a concrete vault. The spans are 29'7" and 24'....The plan dictates #9 at 12 o.c., top and bottom, both directions. The section illustrates the rebar in the 29'7" direction to be installed first...in the field the bars in the 24' direction were placed first.
Considering the bars are of the same size, does it really matter which is installed first?
Considering the bars are of the same size, does it really matter which is installed first?






RE: Two-Way Slab-Order or Rebar Placement
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RE: Two-Way Slab-Order or Rebar Placement
Technically it does affect the flexural capacity if the shorter span bars are placed closer to the top and bottom surfaces. However, the loss of moment capacity for the longer span would only be ~4% and at a slab thickness-to-span ratio of 1:10 I seriously doubt whether flexural capacity would be the governing failure mode anyway.
Shear capacity should not be affected. Negative moment capacity only comes into play if this slab is continuous beyond the stated perimeter to more distant supports. The only other reason the top bars could matter would be for positive moment ductility or for ridiculously high uplift forces like bouyancy or blast.
RE: Two-Way Slab-Order or Rebar Placement
See Section picture below
RE: Two-Way Slab-Order or Rebar Placement
RE: Two-Way Slab-Order or Rebar Placement
I don't agree with this logic. It doesn't matter much here because the thickness of the slab is large relative to the diameter of the bars. The potential change to the effective flexural depth is minimal. If this were a 10" slab, we'd be having a very different conversation.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Two-Way Slab-Order or Rebar Placement
RE: Two-Way Slab-Order or Rebar Placement
RE: Two-Way Slab-Order or Rebar Placement
Dik
RE: Two-Way Slab-Order or Rebar Placement
That said, in the OP's case as shown in his section, with very thick wall supports, the designer may count on developing negative moments.
RE: Two-Way Slab-Order or Rebar Placement