I would say if you have to guess which way a strong wind will blow and try to
figure out whether a tower will be stronger in one orientation versus another
in order to sleep better the plan is marginal and a wind that is even 10 mph
stronger than what you think you may experience will be a problem. Same goes
for making sure you turn the antennas in a certain direction before the big
wind blows. If that is the case, the installation is marginal.
Stan, K5GO
Sent from Stan's IPhone
> On Oct 5, 2014, at 4:02 PM, "Gene Smar" <ersmar@verizon.net> wrote:
>
> TT:
>
> 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
>
>
>
>
>
> -----Original Message-----
> From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
> Patrick Greenlee
> Sent: Sunday, October 05, 2014 2:06 PM
> To: towertalk-bounces@contesting.com; Cox, Norman R.;
> towertalk@contesting.com
> Subject: Re: [TowerTalk] Is A Tower Weaker in Some Directions?
>
> Norm, Bill is right but hasn't dropped the other shoe yet. Will some
> mechanical engineer type please tell us which direction of lean is strongest
>
> in a triangular tower with X-braces or the typical zigzag bracing. Do you
> want a flat side toward the wind or the side opposite.. For reference lets
> assume one leg of the tower is toward the north. Then one leg is at 120
> degrees and the other is 240 degrees. Which wind direction(s) would be the
> most dangerous for the tower?
>
> One would guess there are three directions of wind that hit the tower at its
>
> least strength and three where it is the strongest. The question is in the
> above example of a tower what would be the most dangerous wind ,one from the
>
> north, 120, or 240 degrees or would worst case(s) be 60, 180, or 300
> degrees?
>
> If there is a substantial difference in max wind vs relative bearing of the
> wind then those with rotating triangular towers might want to be guided by
> this as regards where to leave the tower when not in use. ...and the rest
> of us might wasn???t to consider this with respect to our triangular towers.
>
> Oh woe is me... I have already committed 3 out of 4 towers to their final
> positions with no regard to wind direction. I have 49 ft of Rohn 25 plus
> mast to erect and have not poured the foundation for the tilt base yet (whew
>
> just in time.)
>
> Patrick
> -----Original Message-----
> From: Bill Aycock
> Sent: Sunday, October 05, 2014 11:45 AM
> To: Cox, Norman R. ; towertalk@contesting.com
> Subject: Re: [TowerTalk] Is A Tower Weaker in Some Directions?
>
> Norm--
> Be cautious about your assumptions. The direction of the strongest winds
> does not correlate closely with the direction of the storm path. I one did a
> study for a Rocket test site, (over 30 years ago) that showed (for that
> site) that the strongest sustained wind was almost 90 degrees from the storm
> path. The strongest winds are the result of rotation, not path.
> You might consult your local Weather office for help.
> Bill--W4BSG
>
> -----Original Message-----
> From: Cox, Norman R.
> Sent: Saturday, October 04, 2014 4:41 PM
> To: towertalk@contesting.com
> Subject: [TowerTalk] Is A Tower Weaker in Some Directions?
>
> Dear Group:
>
> I just joined Tower Talk -- I've read through the last 5 years of
> archives and have certainly learned a lot I did not know. What a resource!
> I have a question:
>
> I have just ordered a US Towers HDX-555 tower. At my QTH, I have the
> option of orienting the base plate in any direction I want to. My question
> is: Are these 3-legged towers weaker (or stronger) in some directions than
> others? (I am not a structural engineer.) The reason I ask is that most of
> the violent storms that hit here usually come from the same direction. Will
> orienting the base plate in a certain direction make it any less vulnerable?
>
> Thanks!
> Norm
> KE0ZT
>
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