GUYWIRE FAILURES
I have seen two guyed towers which fell over in high winds due to a
failure in the guy wire assembly. In both cases, TWO CABLE CLAMPS were
used at each termination and the cable was NOT "served" as recommended by
Rohn.
The guy wire simply pulled through the cable clamps.
Cable clamps can work loose and it is a good practice to inspect and
tighten them annually. Rohn recommends using THREE clamps AND serving
the wire at each termination. (Some of my older towers use THREE clamps,
without serving, only at the anchor, where I can check them annually.)
A better solution is to use PREFORMED GUY GRIPS. In 1994 a possible
tornado came through my woods, taking out over 30 trees, including a
couple of 75 year old 100 ft high Oaks. Two 70 foot poplars fell against
the top 1/4 inch guy on my 130 ft Rohn 35 tower. The guy wires
stretched, the top of the tower was pulled about 1 foot off center, but
THE GUYS HELD THE TREES UP! Preformed guy grips were used for ALL
terminations, including at the anchor.
Guy grips are MUCH easier to install than cable clamps and cost about the
same as three high quality clamps.
There is nothing STRONGER or SAFER than a properly installed GUYED tower.
ALUMINUM TOWER FAILURE
If you look carefully at the HEIGHTS and UNIVERSAL ALUMINUM TOWER
sections, you will notice they use Z bracing, similar to Rohn with one
foolish exception: There is NO horizontal piece at the top of each
section. This is
probably not signifigant if only STRAIGHT sections are stacked, but most
of these towers are installed as SELF-SUPPORTING TAPERED TOWERS.
On the TAPERED sections, the TOP of each leg is bent inward and has ONLY
ONE (diagonal) brace! When installed as a self supporting tower, the
(fully braced) bottom of the next section applies a downward and inward
force on this unsupported tapered leg.
One of the locals installed an 80 foot (tapered) self-supporting Aluminum
tower
with a KT34XA on top. He claimed it was withing the published ratings
for the
tower. THREE WEEKS later, it was on the ground. The top leg of the
bottom
section folded inward and the whole thing came down in the street!
I am amazed that the ALUMINUM tower manufacturers continue to produce
tower WITHOUT full bracing at the top of each section.
de Tom - N4KG
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