Do you need special nuts to develop the tensile capacity of higher grade anchor rods (like Grade 55 or Grade 105) for uplift conditions?

The weak point will still likely be the concrete; however, if you can develop the tensile strength of the anchor bolt, then I would use a heavy hex nut.

Good question. Here's an interesting link:
Link
It would appear that for Grade 55 you don't need anything special, just the same A563A Hex or Heavy Hex (depending on the bolt size) nuts you would normally use. For Grade 105 it looks like you need A563DH Hex or Heavy Hex.

As a side note, I usually try avoid higher grade bolts altogether. Grade 105 bolts cannot be welded, giving you one shot to get it right in the field. Grade 55 bolts can only be welded if you specify them as "S1". Also, if the rods get bent in the field, Grade 36 rods can be cold bent back into place, higher grades can't.

Typically with anything other than Grade 36, you're pullout strength will limit the strength of your anchors unless you have very high strength concrete. Also, if you need to get any ductility out of the anchor connection for seismic design, it's very hard to get the pullout strength of the anchor rods to be greater then the tensile strength of higher grade anchors.

Breakout strengths also have this problem, since fewer rods are needed, makeing the breakout prism smaller. However breakout strength can be mitigated with tension reinforcement.

Pick up that 2,000 lb phone and call the mfg. They will know!!

DCBII - Nice link. I was hoping to find something more official from an engineering institute (like AISC), but that is a good start. I am curious about the capacity of the nut to rod interface.

Mike - Are you sure about that? I don't always trust the manufacturers to be well-versed in allowable engineering capacities.

Something I have used in high tension connections in concrete is an embedded plate on the end of the nuts, like a giant washer. Then design for "reverse" punching shear in the foundation. I also put rebar in both directions on top of the plate for "insurance".

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Something I have used in high tension connections in concrete is an embedded plate on the end of the nuts, like a giant washer. Then design for "reverse" punching shear in the foundation. I also put rebar in both directions on top of the plate for "insurance".

That's an interesting idea. How thick of a plate do you usually end up with?

I usually switch over to A615 threaded rods (aka Dwyigdags) whenever the tension is too high to make work with ACI Appendix D.

The grade nut you need in order to develop the material is given directly in ASTM F1554, assuming that's the anchor rod spec you're referring to. I would assume that comparable materials, such as ASTM A 193 Gr B7, would be similar in requirements to a grade 105 F1554 rod, for example.

From Portland Bolt...

http://www.portlandbolt.com/technicalinformation/a...

Dik