Kirk,
Another idea is to copy the Rohn 65 guy bracket concept. There are 3
u-bolts as shown in
http://www.solidsignal.com/pview.asp?p=GA65GD&utm_campaign=base&utm_medium=pla&utm_source=google_base&gclid=CIWE9JXIgcoCFUhlfgodlfAOXg
The concept is the load is transferred to the cross "Z" bracing directly
with two "u-bolts", not thru the welds of the Z to the legs, or at a
single plane. Then the third u-bolt attaches to the leg. Thus all four
Z brace members are sharing any asymmetric guy loads and distributing it
in tension to the other two legs at four points. No accessory load
sharing assembly is used on R65 to the max height permitted (500').
However, the Z brace u-bolts are specially formed to fit, not available
except from Rohn. If you can figure out a way to bend some stainless
rod with threaded ends to shape this might work.
While a 20' up and 20' derrick will reduce the lifting load, a 20'
derrick is a pretty ambitious length for column buckling loading with a
backstay. Side guys are a must, IMO, maybe guys at 10' and the top.
see http://www.engineeringtoolbox.com/euler-column-formula-d_1813.html
for some concepts. I think the derrick for my HDX589 is about 7' tall
and is braced with 2x2"x.25" tube, uses 3:1 blocks and a serious winch
that takes a lot of effort for a tower several times the lifting moment
of what you are planning.
A small disagreement with Hans' - the bending moment on sections above
is independent of the attachment height of the lifting cable.
Grant KZ1W
On 12/28/2015 16:22 PM, Hans Hammarquist via TowerTalk wrote:
Hi Kirk,
First: I suggest you attach the lifting cable between the third and fourth
section (22-TARP and 18-TARP). That will minimize the load on the top sections
and at the same time give you a better attach angle on the lifting cable.
I am using a plate I custom made that fit between the sections. It has three
holes, one for each leg. The legs of upper section fit rather precisely in the
holes and at the same time the plate rest in the lower section. I attached the
guy cables in other holes, drilled in the plate. That way the guying force is
spread between the three legs.
I was told that you should never attach a guy or lifting cable directly to a
leg as you may pull off the leg from the cross member, some not good. If you
want to put a wire to the tower, wrap the wire to include the cross member.
If you check through the photos of my tower installations you find a photo of
that plate:
https://www.facebook.com/media/set/?set=a.10150198503693539.328964.579753538&type=1&l=b4a8463457
I know it's not the cheapest way but I think it's one of the better.
Good luck,
Hans - N2JFS
-----Original Message-----
From: Kirk Kendrick <kmkendrick@gmail.com>
To: towertalk <towertalk@contesting.com>
Sent: Sun, Dec 27, 2015 10:34 pm
Subject: [TowerTalk] Attaching winch cable to Universal Tower
To those of you who have used aluminum towers:
QUESTION: What's the best method to attach a raising cable to an aluminum
tower?
I'm looking for ideas on how to attach a winch cable to raise and lower an
HD 21-50 Universal Tower with about 100# of antenna gear at the top. I'm
worried that the forces during tilt up/down could damage or deform the
aluminum tower near the attachment point. Anyone have a design of an
attachment method/fixture that minimizes this risk?
I'm NOT looking for a "temporary" solution (that is, no "lifting straps"
that would deteriorate in the weather). The gin pole, winch, and cable will
remain attached so the tower can be lowered (by one person) whenever
needed. My hope is that the tower and raising fixture will be up for years
of service.
NOTE: My plan is a raising fixture consisting of a 20' gin pole with back
stay, winch bolted to gin pole, cable from winch through pulley at top of
gin pole to an attachment point 20-25' up the tower.
I'm sure some of you have already solved this attachment issue...and can
share successes (& approaches to avoid)
Tnx in advance,
Kirk KK2Z
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