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RE: What Exposure to use?

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Dennis,

I have the same questions.  I was in southeastern Arizona and could look out 
across the valley for 40 miles or more with nothing obstructing my vision 
or the wind.  It was the same as standing on the sand dunes of the barrier 
islands on the south shore of Long Island, N. Y. and looking out over the 
Atlantic Ocean.  I have stood on a bluff on the north side of Tucson that was 
100 feet or more above the valley floor and pondered this wasn't any 
different than the top of a 10-story building.

Basically, I consider the site and use what I feel represents the 
conditions.  If I thought that Exposure D was most appropriate, I would use 
it.

I would not try to cut it too tight with pole signs.  Traffic signs 
(admittedly not the most wind resistant in the world) have a tremendous 
amount 
of rotational flutter in even the lightest of breezes.  That the flutter is 
not ordinarily visible in pole signs does not mean that the same forces are 
not there.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Dennis Wish wrote:

. > This is where I started to read more into the code than was written. For 
. > my own edification, why is there a likelihood of greater wind exposure 
. > over a body of water for say a mile than in the middle of a desert for 
. > the same distance. I suppose this is what I did not understand. In most 
. > case we use Exposure C in areas where there are homes  - even farm homes 
. > in surrounding areas where I can see that we take into consideration 
. > trees, houses and other structures that can block a gust of wind.

. > However, here in the low desert it is very likely to have one building and
. > nothing taller than a rock for a mile or more. Although I read the code 
. > for what it said, I wondered if the interpretation was such that only a 
. > body of water is considered unobstructed by anything that might act to 
. > reduce or deflect the wind from a structure. If this is true, why would 
. > it not be true in an open area such as might be found in the Dakota's, or 
. > the Panhandle and deserts known as "Dust Bowls".

. > I hope you see my point - it's simply one of learning.

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