[TowerTalk] Re:specification formulas (was about areas)

Bill Aycock baycock@hiwaay.net
Mon, 24 Aug 1998 08:55:57 -0500


Steve- Thanks very much for taking the trouble to look this up and send it
to us.

However, there is still a problem in these equations- they only make sense
if the velocity factor is in Miles/hour, not feet/second, as given.
the conversion is the ratio 88/60 to convert miles per hour to feet per
second-- this factor squared times the density/2 value, 0.00119, does give
the 0.00256 value you show.  

Is it possible that the units given for velocity have been in error in this
spec for YEARS?  I know the wind speed factor is almost always given in
mph, not ft/sec, in the graphs used to tell what is to be used in local
areas, but this table uses ft/sec- ??

Bill

At 11:08 PM 8/23/98 -0500, you wrote:
>The actual set of formulas used in the EIA standard is:
>
>F = qz * Gh * [ Cf*Ae + SUM(Ca * Aa) ] 
>qz = .00256 * Kz * (V^2) 
>Kz = [z/33]^(2/7) 
>1.0<=Kz<=2.58 
>Gh = 0.65 + [ 0.60 / (( h/33)^(1/7)) ] 
>1.00 <=Gh<=1.25 
>except for tubular towers where Gh = 1.69
>
>Where 
>z is the height in ft of the section of interest
>h is the overall height of the structure
>v is the velocity in ft/sec
>F is the force of the wind on item under investigation 
>qz is the velocity pressure
>Kz is the factor to account for increasing wind velocity with increasing 
>height. 
>Gh is a gust factor that is also based on height and structure composition.
>


Bill Aycock   W4BSG
Jackson County, AL
EM64vr
W4BSG is "vanity" this time, but was 
earned by exam in 1954, the first time.

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