3-Way vs. 4-Way GUYING de N4KG
The 3-way vs. 4-way guying was analyzed some time ago on this
reflector. Bottom line is that WORST CASE for 3 way guying is at
30 degrees to the wire (parallel to one of the tower faces). The
extra load compared to straight on is approximately 15% (1/cos30).
BTW, if the wind bi-sects two guys spaced 120 degrees, the
load on those guys is the same as the load on a single guy
if the wind is coming in line with that guy.
The notion that 3 way guying is 45 times more linely to fail
than a 4 way system is a total MISAPPLICATION of probability.
Whether the load is carried by one or two guys is meaningless.
The only concern is whether the guy is strong enough to carry
the whole load under the worst case situation.
Note that Rohn shows less than 80% guy anchor spacing for
their FOLD-OVER towers. The MAJOR justification for this
recommendation is that the MAXIMUM HEIGHT is only 48,
58, or 68 feet. The 15% reduction in load with 4 way guying
is a only minor secondary contributing factor. SHORTER
TOWERS have LESS LOAD than tall towers.
de Tom N4KG
(7 towers still standing with 3 way 80% guying after a small tornado
took out dozens of 70 ft trees in my woods in 1994, including a 130
footer whose top guy wire held up two 70 ft poplars which fell across
it!)
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