[TowerTalk] Q on guyed rotating towers

[kr7x1 at verizon.net]

Jim/Arthur:

Rotating towers tubular/cantilevered like berthas or triangular trussed like Rohn with rotating guy rings need to have some point fixed against rotation somewhere in their height to develop the resistance to allow the mechanism that rotates them to work. This is also the place that resists any torsion applied to the tower system by external forces,i.e., eccentric wind load on the antennas.

The torque is usually resisted by the rotating mechanism be it a gear and chain or direct coupled system. This is the fixity that both resists the torque and allows the tower to rotate.

The tower structure itself (tube or triangular trussed section) has to transmit this torque force say from the antenna location to the point of resistance. Tubular towers do it thru hoop stress and trussed triangular towers thru the diagnol members.

Dick Weber, K5IU, published a paper a while back in QEX, I believe, on the effects of torsion on towers and how to mitigate it.

IF you dont have a mechanism to resist the torsion created in the tower, it would not turn or it would spin like a top.

I don't know of any brake mechanism that is utilized at the rotating guy rings to keep the tower from rotating.

Regards
Lonberg Design Group, Ltd.
H.S. Lonberg, P.E.,S.E.
President

>From: jimjarvis at optonline.net
>Date: 2008/02/28 Thu AM 11:56:17 CST
>To: towertalk at contesting.com
>Subject: Re: [TowerTalk] Q on guyed rotating towers

>Comments bottom-postedFrom: "Arthur Trampler" <atrampler at att.net>Subject: [TowerTalk] Q on guyed rotating towers<snip>From what I understand part of the strength of a guyed tower is that torsional movement is converted into down force by the guy wires tightening as they attempt to cover a greater distance (as the tower twists).With a rotating guyed tower, is there some sort of locking mechanism between the bearings and tower, at least in a given "parked" position to allow this phenomenon to occur?  Otherwise it would seem that this benefit is lost as the guys are not attached to the tower, but to the bearing rings.Help me out...maybe the difference in strength is inconsequential or mitigated by other factors.Art, K?RO-0-The strength of the tower is the strength of the tower, based on the materials and design.  LOADING on the tower comes from mass and surface area, as the wind works on the structure.   Loads are transferred into vertical compression by the guy system.  Torsional loading on a triangular tower indeed does add to the down force somewhat, but this is quite small compared to the other loads.   Thus, a tower which rotates inside a ring-coupled guy system is simply relieved of whatever torsion loading might otherwise be imposed upon it.   It is neither stronger nor weaker as a result.Make sense?n2ea
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