[TowerTalk] Fwd: Guyed + self supporting /2 ??

Patrick Greenlee patrick_g at windstream.net
Sat Oct 18 16:48:16 EDT 2014


I have taken down a 40 ft tower with legs on 14 ft centers.  It is the 
bottom 40 ft of a 100 ft tower that had a failure and crashed down. I took 
it down, transported it to my ranch and reassembled it, raised it and 
lowered it for modification.  I am familiar with a "tipping point" 
phenomenon.  I used an A frame/gin pole in the falling derrick approach to 
do my repetitive lower/raise evolutions.  Because of the width of the base 
(triangular tower with legs on 14 ft centers) you have to pull the tower 
toward its lay down position to get the center of gravity past the two 
hinged legs before the tower tries to fall and takes tension in the winch 
line that passes over the A frame and on to the top of the tower.

Similarly, when raising the tower by tensioning the winch line passing over 
the A-frame to the top of the tower, as the CG passes the "tipping point" 
(CG passes an imaginary line running between the two hinges ) the tower will 
try to fall forward to its final position.  A "tag" line is used to hold the 
tower from falling the last few feet into place. l attached the tag line to 
my tractor and drover the tractor slowly forward to lower the tower into its 
fully erect upright position.

With towers that have  a narrow enough inter-leg dimension this "inflection" 
in the cable tension is likely unnoticed.  So long as there is a line or guy 
or... to keep the tower from continuing past vertical, narrow towers should 
not present much of a problem.  With my 14 ft interleg spacing, ignoring the 
phenomenon could lead to danger and damage.

I just this afternoon finished installing the last of 42 each 2x2x 1/8 angle 
iron -braces on the tower mentioned above.  Next to build a deck on the top 
and a staircase leading to the top. I won't be climbing this tower or the 
free standing tilt-over tower I will be installing on top of it.  I will 
walk up the stairs (with hand rails) and stand on the deck/observation 
platform on top to raise/lower the crank-up tilt-over antenna atop the 40 ft 
base tower.

73

Patrick NJ5G

-----Original Message----- 
From: TexasRF--- via TowerTalk
Sent: Saturday, October 18, 2014 11:11 AM
To: richard at karlquist.com ; hanslg at aol.com ; towertalk at contesting.com
Subject: Re: [TowerTalk] Fwd: Guyed + self supporting /2 ??

Hi Rick, I have used the falling derrick system on towers up to 60ft. I am
not familiar with the tipping point phenomenon so you might elaborate on
that a  bit.

73,
Gerald K5GW




In a message dated 10/18/2014 9:05:28 A.M. Pacific Daylight Time,
richard at karlquist.com writes:

An  additional consideration in tilting up a
tower in one piece is how much  guying is needed.
While Rohn 25 can be tilted up, it typically
requires  multiple levels of guying just to be
tilted up.  This is without any  consideration
of wind.  This in turn rules out a simple gin
pole or  crane and requires a falling derrick, which
pulls on both the upper and  lower guys.  A
lighter weight tower with greater strength
such as  an aluminum self supporting type can
be tilted with a simple gin pole using  one
lift point.  Additional levels of guying for
wind purposes can  still be used after erection
is complete.  Falling derricks have their  place,
but are definitely more complicated, and are
harder to control  because of the tipping point
phenomenon.  You essentially need dueling  winches
to get through the tipping point.  If anyone
has solved  this problem, please let us know.

Rick  N6RK
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