I have purchased a tower that I will soon be moving and wanted to get some
opinions about using it unguyed.
This is actually a construction elevator "mast" made by a company named "Alimak
- Scando-I." This thing is amazingly strong, roughly 2' square, 3" steel pipes
with welded "H" cross members of 3" angle iron, and "Z" cross members of one
inch tubing. One five foot section is well over 200 pounds. It is rated to
support 25 workmen and about two and a half tons of elevator car and ballast
weight (vertical load). It is rated for these loads when tied to an adjoinging
structure every 25 to 30 feet, but the top section can be free-standing up to
25 to 40 feet above the last support. It is currently set into a large chunk of
concrete and free-standing to a height of almost 90 feet and has been there for
a number of years. Each mast section ties to the next with four 1" UNC bolts
(forgot to notice what grade), and insert bushings to splice the 3" vertical
tubes. There are six threaded bushings (5/8" UNC)intended for mounting a gear
rack welded to each section, three on each of two sid
es, which will be handy for mounting antennas and cable anchors.
I want to use it on a mountain top where it will see much higher winds than it
currently does, but we are only planning to put a variety of low wind-load
VHF/UHF antennas for repeaters, nothing like an HF beam. I have a book of the
manufacturer's data for the tower, but there is no data for using the mast
sections as lightly loaded free-standing towers. Just specs like those I have
given related to the "system" application as an elevator.
I have some better pictures if anyone is interested in seeing them.
If this thing will support four or five tons at 25' in the air freestanding,
should I be at all worried about a few hundred pounds of antennas at 85' in the
air? The problem of course is that the loads it is designed for are primarily
vertical crush loads, but still this thing is VERY beefy. The only thing that
worries me a little is wind-induced harmonic motion gettting its own mass
moving against it. I can go get it engineered, but I don't have any
manufacturer's specs for the mast sections alone, or for this application. I do
have a very cooperative rural building department that will not be a problem. I
am just concerned with not losing the tower and antennas (not to mention
whatever they might fall on). I have thought about running some very steep guys
up about half way just to dampen the sway in a wind.
Interested in thoughts from any tower experts out there.
Tom - KD7DMH
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