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@optonline.net
>Date: 2008/02/28 Thu AM 11:56:17 CST
>To: towertalk@contesting.com
>Subject: Re: [TowerTalk] Q on guyed rotating towers
>Comments bottom-postedFrom: "Arthur Trampler" <atrampler@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
>_______________________________________________
>
>
>
>_______________________________________________
>TowerTalk mailing list
>TowerTalk@contesting.com
>http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|