Well Jim,
With a working force of 10 000 lb and a pull-out force of 15 000 to 28 000 lb
gives you a safety margin of 1.5 to 2.8. Would you trust that?
What I remember from my engineering school time you need a safety factor of 4 -
8 to trust a structure, 4 for static load and 8 for dynamic load. You have to
include fatigue etc. I am not talking about the fact that bolts corrode over
time. Is a tower static or dynamic load? There are probably no vibrations of
any significants but varying wind would probably put it in the dynamic category.
Hans - N2JFS
-----Original Message-----
From: jimlux <jimlux@earthlink.net>
To: towertalk <towertalk@contesting.com>
Sent: Sat, Mar 24, 2018 11:31 am
Subject: Re: [TowerTalk] Achor bolts?
On 3/24/18 6:34 AM, Hans Hammarquist via TowerTalk wrote:
> Dear towertalkers,
>
> The are claims in a discussion on Face Book that an anchor bolt, "5/8 in. x
> 12 in. Hot-Galvanized", is suitable for a free standing tower. Someone even
> claims it is used for a 400' freestanding tower. It doesn't make sense to me
> but I might be overly pessimistic.
>
> I hate to start lengthy discussions and this might be one of them so, please,
> comment only if you have a well grounded answer. I'm sure there are plenty of
> opinions about it like my own, but I would like to know if my guts feeling is
> right or wrong. What I am afraid of is that you can pull out an anchor bolt
> like that right out of curred concrete.
>
There are standard "pull out force" tables for chemical anchors (bolts
epoxied into concrete)
Looking over some catalogs, it looks like the standard embedment length
for 5/8" is in the 7-9" range. Pull out ranges from 15,000 to 28,000
lb, depending, it seems, mostly on the concrete (because typically, the
adhesive is stronger than the concrete)
So how much force are you putting on those bolts in your freestanding
tower? 100 lb at the top of a 100 foot tower is 10,000 ftlb moment, and
if the tower is 1 foot wide, that's 10,000 lb load on the upwind bolt.
So, the bolt would hold.
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