Achieving Composite Behaviour
Achieving Composite Behaviour
(OP)
I have a grade beam with dowels sticking out on the top surface of grade beam and are spaced every 48 inches. The slab on grade will be poured over the grade beams and will set on the dowels. How can I determine whether or not I will have composite action in such a way that my rectangular stress block would be on the slab on grade as opposed to the grade beam. Would the calcs/equations be identical to that of steel composite beams with concrete deck?
Also, the slab on grade has rebar at mid-depth. When the grade beam spans continuously above a pile, would my grade slab not crack quite a bit at that location? Do I not have to add extra rebar on the parameter of the slab on grade which is where my grade beams are?
Thanks all.
Also, the slab on grade has rebar at mid-depth. When the grade beam spans continuously above a pile, would my grade slab not crack quite a bit at that location? Do I not have to add extra rebar on the parameter of the slab on grade which is where my grade beams are?
Thanks all.
Clansman
If a builder has built a house for a man and has not made his work sound, and the house which he has built has fallen down and so caused the death of the householder, that builder shall be put to death." Code of Hammurabi, c.2040 B.C.






RE: Achieving Composite Behaviour
BA
RE: Achieving Composite Behaviour
I didn't think 48" c/c would achieve composite action either. But I'm curious as to how one can determine the spacing of dowels required in order to achieve composite action.
Clansman
If a builder has built a house for a man and has not made his work sound, and the house which he has built has fallen down and so caused the death of the householder, that builder shall be put to death." Code of Hammurabi, c.2040 B.C.
RE: Achieving Composite Behaviour
BA
RE: Achieving Composite Behaviour
It does not behave like two steel beams as the distribution of shear is not through a uniform material.
RE: Achieving Composite Behaviour
RE: Achieving Composite Behaviour
If you need flexural strength from both, then do as BAretired mentioned - provide stirrups and top bars and treat the complete section as a beam. Now the slab is fixed on the support beam, and the combined section is L-shape edge beam.
If you simply wanted to prevent separation of the two, then the dowells will do. However, the moment capacity along esge of slab is difficult to evaluate/determine, thus, it (the slab) should be treated as pinned on the support beam.
RE: Achieving Composite Behaviour
RE: Achieving Composite Behaviour
RE: Achieving Composite Behaviour
RE: Achieving Composite Behaviour
What that means is, a short little dowel isn't going to cut it. For #4 bars in 3000 psi concrete, you'd need 22" of development length. For a hook, you'd need a hook length of 8". With 3/4" cover you'd essentially need to hook the bars and use a 9" thick slab.
You cannot use As(req'd)/As(provided) to reduce this per ACI 11.7. So composite action technically isn't possible without the thick slab and the development length established.
Factually, there will be some composite action developed, but it could not be "calculated" per ACI or shown to work without specific testing.
RE: Achieving Composite Behaviour
RE: Achieving Composite Behaviour
RE: Achieving Composite Behaviour
BA
RE: Achieving Composite Behaviour
RE: Achieving Composite Behaviour
asixth, I would be interested to see how the Australian concrete code deals with this. Eagerly waiting for the scan.
Clansman
If a builder has built a house for a man and has not made his work sound, and the house which he has built has fallen down and so caused the death of the householder, that builder shall be put to death." Code of Hammurabi, c.2040 B.C.
RE: Achieving Composite Behaviour
RE: Achieving Composite Behaviour