<...Five months ago I took down a 40 foot heights tower. It had been up
since
the 60s. Larry went SK qrt. We lowered the kt34 and the 2 meter beams,
then we just tilted it over !!! The Big Aluminum ADVANTAGE!
While taking out the bolts, they twisted apart. We discovered they were
rotten in the middle, disintegrated ! >>>>
I believe I may have commented on this historically, but will do so again.
I have in Minnesota (and in Idaho) Heights aluminum towers (among others). I
found in Minnesota that after about 8 years there had been enough
electrolytic action between the aluminum and the steel bolts used to pin the
legs in place that there was substantial space between the edge of each hole
and the bolt.
I bought stainless steel rod of the required diameter and cut the rod into
pieces that would allow me to insert it in place of each bolt with
approximately 1/2 inch extending on each side of the leg. I predrilled the
rod ends to allow a 1/16 inch stainless cotter pin to be inserted. I also
put a stainless steel flat washer on each side of the rod before pinning the
rod with the cotter pins. The stainless rod can slide very slightly in the
hole when there is no downward pressure on the rod.
The tower does not need the bolts to apply force from side to side on the
leg --- it only needs to have something to prevent the inserted leg from
moving up or down.
The 'improved' tower has been in place in Minnesota for over twenty years
with no sign of deterioration of the stainless pins.
As Tom, N4KG, mentioned, there is an opportunity for water to enter at each
joint. I applied a non-acetic acid curing flexible caulk at each leg
junction when I inserted the stainless pins. I check the tower twice each
year for breaks in the caulk (none so far), problems at the pinning points
and for all other antenna, rotator, bearing and cable run points which might
deteriorate in the heat of Summer or the cold of Winter. Everything but the
stainless pins and the caulk has required attention from time to time. The
tower sections show no signs of failure to this point. The antenna at the
top of this tower is a KLM-34XA. It is at 90 feet. The tower has one set of
"limp" guys which apply force only when the top of the tower deflects at
least five inches. They are intended to provide a downward force to counter
the extension force on the side of the tower toward the wind. The theory of
this may be bad (or good) but in practice the tower has survived winds in
excess of 65 mph without damage (that I have been able to discern). The
bottom sections of the tower are 26 inches on a side with double welded
Z-members and double thickness tube walls. I believe these are comparable to
the 30 inch sections now available from Heights. The top sections of the
tower are 18 inches on a side.
If the frequency of high winds was greater than it is for my location or if
I was loading the tower with more than approximately 10 square feet of
antenna I might well consider a different choice than aluminum for a tower.
Given the circumstances I have, I am comfortable with my choice.
Tod, KOTO
________________________________________________________________________
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