A direct hit by a tornado is one of those "Acts of God" that you can't
engineer against, like having a plane fly into your tower. We had a local
occurence where a plane hit a guy wire on 700' tower. Sheared the wing off
the single engine Cessna but the tower stayed up. Now if it had been a
direct hit on the tower, it would have been a different story. Anyway, in a
tornado, a bigger threat is the neighbor's garage roof blowing off in the
gust front away from the tornado and taking out your tower.
I don't use the UBC, very much prefer and recommend Electronic Industries
Association standard 222 rev E (EIA-222-E). They basically don't recognize
anything other than Exposure C and have an extra factor based on height of
the structure. They also do a better job of specifiying how to calculate
the effective area of everything that is hanging in the breeze. They use it
on everything up to 2000' so it gets a little hairy.
There is an even more strigent international standard that is used in
Europe.
de n0vyv steve
______________________________ Reply Separator _________________________________
Subject: Re: Re[2]: Big, heavy mast
Author: Gary Nieborsky <k7fr@ncw.net> at ccmgw1
To: <towertalk@contesting.com>
Date: 6/20/96 3:52 PM
At 01:40 PM 6/20/96 cst, you wrote:
>>>>50 lbs. per sq. ft. wind gust
>
>My calcs show this as at the top of a 110 ft tower in a 110 MPH wind
>district WOW! You must either live in Alaska, off the coast of NC, on in
>Miami!
>
>Here in the upper midwest I figure 25 lbs. per sq. ft. wind gust for an 80
>foot tower in an 80 MPH wind district.
>
>Guess I didn't know how lucky I was!
>
>de n0yvy steve
>
>
Steve,
What's the gust factor for a tornado?
I based my tower on 90mph with an Exposure C gust factor. Sometimes in the
spring I kinda think maybe D would have been better......
Ain't the UBC fun?
73 Gary K7FR
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