[TowerTalk] FW: Is A Tower Weaker in Some Directions?

[Matt]

>>  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 at contesting.com] On Behalf Of Jim Thomson
Sent: Tuesday, October 07, 2014 2:37 AM
To: towertalk at contesting.com
Subject: [TowerTalk] Is A Tower Weaker in Some Directions?

Date: Sun, 05 Oct 2014 17:02:10 -0400
From: "Gene Smar" <ersmar at verizon.net>
To: "'Patrick Greenlee'" <patrick_g at windstream.net>, <towertalk-bounces at contesting.com>, "'Cox, Norman R.'" <nrc at mst.edu>, <towertalk at 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 





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