Damaged Tower Rescue
I can hear it now - K7LXC:
"I TOLD YOU SO...Do as the manufacturer recommends !"
One of my in-the-ground towers has TWO rusted through legs
at ground level. This tower is 30+ years old and has been in
place at this location for exactly 20 years. It is a TV tower
with NO diagonal bracing, only horizontal steps 1-1/4 inch diameter
every 2 ft. One set of steps is 4 inches in the ground, the next step
is 20 inches above ground. There is NO lateral support from the
rusted through legs and the tower can be twisted about the good leg.
The strength of the remaining rusted stubs below the breaks is
questionable but obviously still minimally adequate since the tower
has not fallen or tilted.
To provide latteral support, I drove three 4 ft lengths of 1/4 by 2 inch
angle iron down alongside each leg to a depth of 28 inches. Then
I inserted a 2 X 8 horizontally between the GOOD leg and the two
rusted legs, wedging in another piece of wood for a snug fit. Finally
I inserted another 2 X 8 between the rusted legs and wedged in
additional boards for a snug fit. The good leg is braced on 3 sides.
The rusted legs are braced on 4 sides. After bracing, the tower is
rigid and cannot be twisted.
My concern is whether and how I should support the weight to
relieve the single good leg. One idea is to simply stack 2 X 8
boards up to the first step (20 inches). Another is to build a box
of 2 X 8's (or larger)and bolt the sides to each leg.
My goal is to brace the base well enough to make the tower safe
to climb and dismantle. I considered just cutting the guys on one
side and letting it fall, but I would have to be very accurate in my
aim to get the tower to land between two guy anchors for two other
towers that are spaced about 20 to 30 ft. And, I would prefer to
save the TH6, TA32, and TH3 mounted at 80, 60, and 40 ft.
FWIW, another similar tower (55 ft with 5L10's at 62 / 36 and 4L15
at 55 ft) with a single rusted through leg was similarly braced 18
months ago and is still standing. I have climbed this tower with
no problem or uneasiness. With TWO good legs it was of course
more rigid even before bracing.
Considered thoughts and recommendations are welcome.
de Tom N4KG
.......................
I added more bracing to the tower base tonight and it is quite rigid
latterally and rotationally. I climbed it to the 10 ft level to remove
a TA33 and 155BA "temporarily stored" on the legs at 8 and 10 ft.
No problem. My friends all tell me to get a bucket truck, crane,
or cut the guys. There is only one direction I could let it fall and
then it would go across the upper two guys for a 120 ft Rohn 25
tower. I suppose I could temporarily move the outer guys (90 ft
from tower) to the lower guy anchor (60 ft from tower) and let it
fall across the fence into my neighbors yard, assuming I get his OK.
His house is >150 ft away.
The bracing is as follows. Legs are N, SE, SW.
A 4 ft 2X8 is laid flat between the N and SE/SW legs.
A short 2X10 is wedged in vertically against the N leg.
A short 2X8 is laid flat between the SE and SW legs, end against the
vertical wedge next to the N leg. Additional boards are placed
vertically
against the SW and SE legs with another vertical board. It looks like
an H from above. Another vertical 2X10 is stacked against the N leg.
Another H is at right angles and above the first H, between the N and
SE / SW legs and flush with the bottom of the first step to provide
load support at each leg.
On the outside of each leg is a 4 ft piece of 1/4 inch thick 2X2
angle iron (painted steel) which is pounded in the ground 28 inches.
I believe the base is rigid and secure but my friends are all advising
caution and recommending against climbing. But they are not
engineering types so are exercising caution in the face of unknown
territory. My feeling is that it is safe to climb but I am open to
additional input. I will call the bucket truck rental place to see if
they have something that will go to 80 ft, can supply an operator,
and whether the bucket can carry the load of assembled antennas.
Thanks for your considerations.
Tom N4KG
___________________________________________________________________
Get the Internet just the way you want it.
Free software, free e-mail, and free Internet access for a month!
Try Juno Web: http://dl.www.juno.com/dynoget/tagj.
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|