[TowerTalk] Antenna & Tower Wind Load Ratings

[Kurt Andress]

Hi Gerald,
This is usually not very useful for most installations......
A K6OK has pointed out, with 222-G the wind pressure applied to the 
antennas are dependent on several site specific variables.
1) Tower System Importance Factor, is the system a critical or 
non-critical part of societal infrastructure.....?
2) Site Exposure. Urban, Open Country, Sea/Lake Side next to open water.
3) Terrain Profile. Flat terrain or Hilltop site
4) Antenna height above tower base
5) Basic max expected wind speed for the geographical location.

So, what the tower designer probably needs is the correct "Projected 
Areas" (one for the sum of the elements and one for the boom) and the 
shapes of members for each (round, or flat/square).
Then, he can apply all the appropriate factors and drag coefficients to 
those "projected areas"to determine the loads those antennas will apply 
to the tower structure where the client wants to place them.
We still aren't getting that yet, so I stuck my neck out to revive this 
discussion (yet again) to see if a reminder might rejuvenate enough new 
"market knowledge", which might in turn be able to put enough pressure 
on these specific product providers to get them to straighten out this 
needless and senseless problem. If we could get everyone involved in a 
room @ Dayton or wherever.....we could straighten this out in about 15 
minutes, but it might actually take an hour or more because it could be 
some kind of fun ;-)

Both the tower designers need to clearly tell us they are rating their 
towers for the antenna "projected areas" (or maybe not?), not making 
guys like me to have to dig thru some of their pages of detailed 
calculations to hopefully be able to figure that out, and the antenna 
suppliers need to provide the correct "projected areas" for each of 
their products.
This is not rocket science and is not difficult to do, it just needs to 
be done so that everyone is finally able to all be on the same page!
73, Kurt, K7NV
P.S.
I have received some separate correspondence from a very well known P.E. 
friend, that has followed this discussion, and has designed a lot of 
towers for us.....he confirmed that all he needed was accurate 
"projected antenna areas and member shapes", and specifically asked me 
to not advise anyone to provide resultant wind loads, because one might 
not know which of the site variables were used to determine them, and if 
they were all defined by the provider, they are most likely to not be 
suitable for the site the engineer is trying to design for!


On 6/16/2017 5:01 AM, TexasRF at aol.com wrote:
> Many of the commercial wireless internet antenna manufacturers specify 
> their antenna loads as pounds or Kilograms of force at a given wind 
> speed. This seems like a non-ambiguous way to handle wind loads
> Gerald K5GW
> .
> In a message dated 6/15/2017 11:13:21 P.M. Central Daylight Time, 
> andresskurt at gmail.com writes:
>
>     Jim Lux,
>     Thank you for contributing to this discussion!
>     I don't think we agree about everything said, but that is quite ok!
>     All I intended to do with my initial post....was to remind those
>     on this
>     reflector now, that what I told them was wrong a couple of decades
>     ago,
>     is still wrong!
>     I'll leave sorting it all out to all you Stellar Experts that
>     chose to
>     take up the challenge......
>     I would warn everyone to not try to outsmart the EIA/TIA-222
>     Standard,
>     we aren't NASA or Boeing, what happens on towers near the ground,
>     is not
>     what happens up at 35,000 ft for Roger, K8IA....
>     One that studies the 222-G mathematics will find out that the the
>     wind
>     pressure gradients go away and become constant at around 400
>     ft.......the member oscillations that K8IA mentions are due to a
>     phenomenon known as "vortex shedding", that is well documented and
>     happens at rather low wind speeds with the antennas we use, when
>     insufficient element taper schedules are present to prevent all of
>     the
>     individual element members to go into oscillations together....around
>     the same range of wind speeds they closely share. I have been on
>     lots of
>     towers to see antennas do this, and have designed elements that
>     don't do
>     this.......
>
>     I feel no longer qualified to hang with all the tremendous Cerebral &
>     Pundit brainpower that has been brought to bear here, so I will
>     kindly
>     back out of this.
>     I accomplished what I wanted to do....simply to remind the current TT
>     readers that after ~ 35 years of trying to get people to do these
>     things
>     right, these simple things are still not being done right!
>     Thanks to all that read it......it's up to you to demand technical
>     correctness from your vendors!
>
>     73, Kurt, K7NV
>     _______________________________________________
>
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