Headed Anchor Rods
Headed Anchor Rods
(OP)
Is there any appreciable structural pullout capacity difference between using an embedded welded nut versus an embedded welded plate on an anchor rod?
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RE: Headed Anchor Rods
RE: Headed Anchor Rods
RE: Headed Anchor Rods
SA = (pi*r1*s1+pi*r1^2)-(pi*r2*s2+pi*r2^2)
where:
SA = surface area
r1 = radius of shear cone at free edge
r2 = radius of cone at anchor head
s1 = length along side of cone from anchor head to theoretical tip of cone
s2 = length along side of cone from fre edge to theoretical tip of cone
RE: Headed Anchor Rods
The next thing I do is size the plate/nut such that I have adequate bearing surface area of the plate or nut to develop the full capacity of the anchor rod, using the ACI equations for bearing on concrete. That way, the rod will yield before the concrete fails in bearing under the head.
For larger rods, a simple nut is not adequate to develop the bearing capacity. For instance, for a 1" rod, the yield strength would be 15 kips, assuming A36 steel. The bearing strength, assuming no edge concerns, would then be 2*0.85*f'c*A. With F'c=3000psi, we would need a bearing area of A=2.94sq.in. So we would need a plate then that was approximately 2"x2". However, a heavy hex nut would only have a bearing area of about 1.5 sq.inch. For 1.5" diameter rod, that plate would need to be 3"x3". This all ignores load factors, which should be used properly, for the sake of simplicity.
I then would check the resulting plate for cantilever bending, assuming 2-way distribution, and shear. Usually I find that using a thickness about equal to the cantilever distance results in a good stiff plate.
RE: Headed Anchor Rods
RE: Headed Anchor Rods
Dik