[TowerTalk] surface area of 45g

[Kurt Andress]

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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