Conservation of Momentum says that that torque energy has to go somewhere. I
agree that the guys will resist it, and using torque bars/limiters probably
helps keep the tower from twisting, initially, but those guys have an elastic
modulus and will stretch. Kurt, K7NV, a SE I believe, published structural
calculations on various tower/guy/antenna configurations. His website seems to
be down right now (either via the N1LO website or k7nv.com) but his conclusions
were that in high winds with decent antenna loads, those towers which have
their based fixed in concrete were most prone to failure; the base is fixed,
the torque energy just twisted the tower apart. A pier pin base allows the
tower to twist free and is a better solution except that, as stated, the guys
will stretch, and in high winds the tower will want to "lean" over. The
standard pier pin base is flat and all the compression forces can be exerted
onto one leg and that leg will eventually buckle. The best bet is
a pier pin with a tapered base. Rohn does make these; they're just special
order. That's what I put up last year for my 120 ft. Rohn 45 with a big 3 el
40M yagi up top; tapered, pier pin base. The tower can twist all it wants and
can lean over all it wants. Even with this base, that tower is rock solid to
climb. I guess, based on my learnings, everyone should understand that torque
bars/limiters may help initially but that energy will have to go somewhere and
in a high wind situation they won't help. The guys will stretch and the forces
will want to go somewhere. Makes sense to me. Phil KB9CRY
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|