[TowerTalk] Rohn Torque Bar confusion

[kb9cry at comcast.net]

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