[TowerTalk] Screw Anchors

[Pete Smith]

At 10:42 AM 7/1/98 -0500, Raymond Dave-CSUS04 wrote:
>
>The biggest problem I've seen with screw in anchors has nothing to do
>with the "screw" portion pulling out of the soil.  I have witnessed one
>situation where the  welds that hold the screw to the rod failed. . .
>the rod pulled nicely out of screw, leaving the screw portion in place.
>Needless to say, the tower went down.  Fortunately, it was not mine.

Two comments:

Seems to me that a lot of amateur installations would profit by anchoring
the top guys separately from those lower down.  That way, you eliminate the
certain loss of the tower in the event of a single guy anchor failure.  You
also can say with pretty high confidence that a tower with two separate guy
anchors in each guying plane will NEVER fall straight out.  That could be a
useful argument if someone wants to enforce a 110 percent set-back
requirement.

One case that hasn't been mentioned is what happens with saturated ground
around a screw anchor.  One of my guy anchors is located in the flood plain
of a seasonal stream, and goes under a couple of inches of water for about
a month every year.  It's the standard Rohn concrete anchor design, so
there's about 3/4 yard of concrete in it, which gives me a lot of
confidence that it'll stay put.  There's no such safety factor with a screw
anchor.  If the soil above one of them turns to soup, I suspect it loses 95
percent (or more?) of its holding power. 




73,  Pete Smith N4ZR
In wild, wonderful, fairly rare WEST Virginia

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