In a message dated 97-04-16 21:42:23 EDT, nw9g@netusa1.net (Steve Narducci)
writes:
> Today the weather was good enough for me to get out and
> start my 100 foot of rohn 25g tower. I went to the farm
> implement store and purchased three 42" screw augers with
> a 6" screw at the bottom which has a 1/2" solid shank with
> a welded loop at the top. I used my post hole digger to
> get down about 8 to 10 inches to get the auger started.
> It was tough but I managed to get the augers down to the
> top of their necks on the ground.
> My question. Is this auger safe for 100 foot of
> tower? How much pull would it take to yank these out of
> the ground? Finally, should I put a bag of cement on the
> top 10 inches of the auger that is in the cavity below the
> ground level? Or would that make any difference at all?
> I am somewhat scared to climb this monster and I just
> want it to be safe. Thanks so much and 73's....
Are these screw-in anchors adequate? Probably not.
The tower construction Prime Directive is to "do what the manufacturer
says". Nowhere in the Rohn literature does it give a spec to USE screw-in
anchors for anything. The one they offer in their catalog (which is bigger
than the one that you mentioned) states that it has 2,500 pounds holding
power.
The A.B.Chance Company publishes an "Encyclopedia of Anchoring" for
screw-in applications. They list nine different classifications of soils,
each with a different holding capacity. Your first problem is that you don't
know what your soil classification is so you can't give it any kind of
rating.
The second thing is the screw-in anchors that you purchased are too
small. If the Rohn one has 2,500 pounds holding power and 3/16 inch EHS has
an ultimate breaking strength of 3,990 pounds, the anchor will pull at about
62.5% of the breaking strength of the guy wire making the screw anchors the
weak link in the chain.
You didn't mention what county you are in or what your wind speed zone
is. That plays a key part in your installation planning.
Cutting to the chase, don't use the screw-in anchors. Install anchors
per the Rohn catalog (available from TOWER TECH for five bucks) and you'll be
able to sleep nights when that big storm comes rolling through.
Congratulations for thinking about the soundness of your decision and
posting your concern on TowerTalk. It was in your best interest.
73, Steve K7LXC
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