I should add that I was considering a free-standing tower (which is what
I have). In the case of a guyed tower, the harder the wind blows, the
more the downward force on the tower legs, all of them. The
cross-bracing insures that the legs all stay parallel and can tolerate
any torsional forces. Torque arms on the gy brackets are intended to
help with torsional loads.
Kim N5OP
On 10/5/2014 2:15 PM, Kim Elmore wrote:
I don't think wind direction matters. However, a leg is in the most tension
when the wind is dead onto an apex. A leg is in the most compression when the
wind is dead onto a face. Beyond that, loads are distributed according to
standard statics. The above cases indicate the maxima for a given leg.
I don't think this is the biggest worry, though. Torsional loads are. These can
be very large with large arrays due to turbulent eddies. Shock loads can be
very high as the arrays bounce against the play in hears and brakes.
Kim N5OP
"People that make music together cannot be enemies, at least as long as the music
lasts." -- Paul Hindemith
On Oct 5, 2014, at 13:06, "Patrick Greenlee" <patrick_g@windstream.net> wrote:
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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--
Kim Elmore, Ph.D. (Adj. Assoc. Prof., OU School of Meteorology, CCM, PP
SEL/MEL/Glider, N5OP, 2nd Class Radiotelegraph, GROL)
/"In theory there is no difference between theory and practice. But, in
practice, there is." //-- Attributed to many people; it's so true that
it doesn't matter who said it./
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