Henry wrote:
>
> To do some begining calculations, I need a few dimensions.
>
> The projected surface area of Rohn 45g (and 25g, to save me from having to
> ask again), like square inches of surface area for 1 foot of tower, face or
> leg frontal.
> A conversion between mph and psi for wind loading, like a wind speed of X
> mph corresponds to a wind pressure of Y lb.s per square inch.
>
> Thanks...........
>
> You'll be held harmless for these numbers.
>
>
Hi Henry,
First, what specification would you like to use as the foundation for
your calculations. There are at least 2 popular ones in the U.S.(EIA &
UBC), and they are not identical.
You would do yourself a great favor by obtaining a copy of the design
spec. Then you can see how all of the factors relating to the
installation are
to be treated.
If you are going to use the EIA spec:
The effective surface area Ae for 25G = .255 SqFt/Lin Ft
45G = .296 " "
This does not include feedlines. For each feedline you get to add:
1/2 Dia Feedline = .050 SqFt/LinFt
3/4 " " = .075 " "
7/8 " " = .0875 " "
1" " " = .10 " "
The EIA wind loads are height dependent. As a minimum you are instructed
to divide the tower up into separate sections between the guy points and
apply the different loads to each span separately. Use the height of the
center of the span to determine the load in the table below.
For antennas select load based on antenna height.
WIND LOAD (PSF) P= .00256 (V^2) (Kz) (Gh) (Cd) (A)
EIA RS-222 E & F
Exposure Gust HEIGHT Basic Wind Speed (Mph)
Coeff Factor
Kz Gh Ft 60 70 80 90 100 110 120
1.000 1.250 30 13.8 18.8 24.6 31.1 38.4 46.5 55.3
1.000 1.250 33 13.8 18.8 24.6 31.1 38.4 46.5 55.3
1.057 1.234 40 14.4 19.6 25.6 32.4 40.0 48.5 57.7
1.126 1.215 50 15.1 20.6 26.9 34.1 42.0 50.9 60.5
1.186 1.201 60 15.8 21.4 28.0 35.4 43.8 53.0 63.0
1.240 1.189 70 16.3 22.2 29.0 36.7 45.3 54.8 65.2
1.288 1.179 80 16.8 22.9 29.8 37.8 46.6 56.4 67.2
1.332 1.170 90 17.2 23.5 30.6 38.8 47.9 57.9 68.9
1.373 1.162 100 17.6 24.0 31.4 39.7 49.0 59.3 70.6
1.411 1.155 110 18.0 24.5 32.0 40.5 50.1 60.6 72.1
1.446 1.149 120 18.4 25.0 32.7 41.3 51.0 61.8 73.5
1.480 1.143 130 18.7 25.5 33.3 42.1 52.0 62.9 74.8
1.511 1.138 140 19.0 25.9 33.8 42.8 52.8 63.9 76.1
1.541 1.133 150 19.3 26.3 34.3 43.5 53.7 64.9 77.3
1.570 1.129 160 19.6 26.7 34.8 44.1 54.4 65.9 78.4
1.597 1.125 170 19.9 27.0 35.3 44.7 55.2 66.8 79.5
1.624 1.121 180 20.1 27.4 35.8 45.3 55.9 67.6 80.5
1.649 1.117 190 20.4 27.7 36.2 45.8 56.6 68.5 81.5
1.673 1.114 200 20.6 28.1 36.6 46.4 57.3 69.3 82.4
Don't forget to apply the 10% guy pretensions, tower section weights,
and antenna weights. If you get the spec it will show you how to
calculate the guy wind loads. That's a bit too complicated for this
medium.
That's a ballpark place to start. Have Fun!
Might want to have a backup battery ready for your calculator :-)
--
73, Kurt
K7NV "That's K7 "Nevada" (ex - NI6W)
YagiStress - The Ultimate Software for Yagi Mechanical Design
Visit http://www.freeyellow.com/members3/yagistress/
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