>> A properly designed and constructed guyed tower will not impose downward
>> force on the legs.
Gene,
Not flaming, but this would be magic. Any wind loading with a component normal
to the axis of the cable increases its tension. Lest Newton roll over in his
grave, that tension imparts reactions at the tower connection with both a
horizontal and vertical components. The vertical component of that reaction
can only be in the direction of the cable - which is downward.
Matt
KM5VI
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Jim
Thomson
Sent: Tuesday, October 07, 2014 2:37 AM
To: towertalk@contesting.com
Subject: [TowerTalk] Is A Tower Weaker in Some Directions?
Date: Sun, 05 Oct 2014 17:02:10 -0400
From: "Gene Smar" <ersmar@verizon.net>
To: "'Patrick Greenlee'" <patrick_g@windstream.net>,
<towertalk-bounces@contesting.com>, "'Cox, Norman R.'" <nrc@mst.edu>,
<towertalk@contesting.com>
Subject: Re: [TowerTalk] Is A Tower Weaker in Some Directions?
If the wind were to blow normal to one face of a tower, the opposite
single leg would be the weakest. Assuming the cross-bracing holds (does not
fail) upon exposure to high winds, the windward legs of the tower will be in
tension, i.e., the wind will attempt to elongate them when they bend away from
the wind. The remaining leg on the opposite side of the tower will be in
compression, i.e., the wind will attempt to force it downward. This sole leg
must withstand this downward, compressive force by itself. It will deform
(bend) when sufficient downward force has been placed upon it, much as a
human's knees would buckle if that human were required to support heavier and
heavier loads on his shoulders.
Now consider the case when the wind is from the single leg side of the
tower and towards the opposite face. The single windward leg will be in
tension and the two opposite legs will be in compression. Unlike the first
example with the wind applied on the face, the two leeward legs of the tower
resist the downward force from the wind with twice the counteracting force of a
single leg. To get this tower's two legs to buckle will require twice the wind
force on the opposite leg vs the single leg example above.
A properly designed and constructed guyed tower will not impose downward
force on the legs. The windward guy(s) will counteract the wind force and keep
the tower erect. The guys should not deflect sufficiently to allow a downward
force to be applied to the leeward leg(s). This is why the foundation of a
guyed tower need not be massive: it will merely resist the dead weight of the
tower and its antenna loads. There will be no wind-caused overturning moment
applied to the base as is the case with a self-supporting tower and its massive
concrete base.
This is also why one must not guy a tapered, self-supporting tower.
Guys impact unnecessary downward vertical force on the structure. If you
believe you must guy a SS structure, then re-check your design and select a
"beefier" tower. And ditch the guys.
73 de
Gene Smar AD3F
## he has a freestanding crank up tower.. US tower corp HDX-555.... not a
guyed 25/45 G type tower. He cant guy the HDX-555, even if he wanted to.
Your structural analysis theory is flawed. You wont see any difference if
any, regardless of base orientation.
## as far as guying a freestanding, tapered tower, its done all the time.
It’s the strongest structure there is. The legs will easily handle the
downward force.
Jim VE7RF
_______________________________________________
_______________________________________________
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
|