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@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@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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