The commercial folks who rent my 120' Rohn 45G tower loaded it up with
24 heliax's and antennas. It finally went over in a measly 106 mi/h
wind last week. The failure was a tension failure of one of the ground
anchor guy rods. It just necked down and gave up, although it appears
that there was a fatigue crack from the last year's 134 mi/h storm.
Before they put it back up, we had a look at the new Rohn catalog.
Guess what? The 5/8" rods are only good for 7300 lbs load, which
doesn't make much sense if the catalog says you need three 6700#
strength guys in each direction.
Next time it goes up with either 3/4" (rated at 17600#) or better
1 1/4" (rated at 49000#). The tower was originally installed in
complete conformance with the Rohn catalog drawings, but now that the
mistake is clear, everyone feels a bit sheepish. And I'm glad it didn't
give way when I was up on the tower, although I wouldn't climb in our
storm winds on a bet. One of the other guy rods was also cracked and
ready to let go. The one that did looked just like the Porsche
connecting rod bolts I used to lose to fatigue fracture when I was
racing.
A word to the wise, check the rating of your guy anchors as well as
your guy cables, and don't use the setups called for in the older
Rohn catalogs without questioning them!
73 de Dave, W6NL (ex-W6QHS)
BTW, I'm back to work, so ham radio will be taking a definite back seat
for the time being.
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: K7LXC@contesting.com
Sponsored by Akorn Access, Inc & KM9P
|