[TowerTalk] Anchor Bolt Grade Suitable for Tower Base?

[Kevin Normoyle]

< I'm interested in this because I'm getting a used tx-455, with some 
3rd party anchor bolts
and it's got me wondering if they're the right ones>

rick wrote:

> It seems to me that the strength of the concrete limits the safe load
> you can put on anchor bolts to a low enough value that ordinary steel
> is good enough for the bolts.

did some more searching. The whole analysis of strength of anchor bolts
in concrete (say for traffic signs) seems to be an interesting area of 
specification/research.

They do say fatigue strength of the bolts might be the real limiter, 
though, rather than yield strength.

In any case, some states allow traffic sign anchors to be designed 
specifying
55ksi yield strength in the anchor bolts. So they must think that you 
can some advantage
up to at least that...i.e. concrete not being the limiter. And they say 
no less than 36ksi.

example: http://www.sddot.com/operations/docs/specbook04/985.pdf

this next report mentions research and shows some examples that would make
it seem like 55ksi could be a valid requirement in some anchor designs. 
(they have
a formula from research, and some examples)

http://manuals.dot.state.tx.us/dynaweb/colbridg/des/@Generic__BookTextView/25066;cs=default;ts=default;pt=19395/*

the astm f1554 spec also covers galvanizing of the bolts and nuts, so 
there are more
issues than just required yield strength.

The whole thing seems to have enough engineering analysis and research, 
that I wouldn't think one
could guess at what would be "good enough".

It may be that the US Tower bolts are way oversized for the requirement 
though, so it could
just fatigue strength/corrosion that are the main issues.

Also: re Steve's comment about grout pads

Saw a note (from the traffic sign world)
that there are mixed opinions about the benefits of grout in a double 
nut joint.

Cracked grout can actually trap moisture. Also you can't 
inspect/retighten the lower nuts.

interestingly here, the florida DOT seems to say their designs will make 
grout pads optional/discretionary
(with screening to prevent debris from going into the joint). This is 
from 12/22/04.
summarizes grout pad issues in double-nut joints

http://www.dot.state.fl.us/structures/Memos/temporaryDesignBulletinC04-08.pdf


-kevin