[TowerTalk] Is A Tower Weaker in Some Directions?

[Kim Elmore]

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 at 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 at 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 at 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./