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# Re: Wind Load Topographic Effects

• To: seaint(--nospam--at)seaint.org
• Subject: Re: Wind Load Topographic Effects
• From: refugio rochin <refugio311(--nospam--at)yahoo.com>
• Date: Tue, 30 Dec 2008 14:43:38 -0800 (PST)

We had a debate in hurricane region in the Caribbean, and had to call in one of the experts who worked on the code to decipher our dispute.  It turned out that the key word for discerning the affect of a region of wind flow is "quadrant" which is indeed a fourth of the area which is open to wind flow !

From: Jeff Smith <jeffsmith7(--nospam--at)comcast.net>
To: seaint(--nospam--at)seaint.org
Sent: Monday, December 29, 2008 12:22:36 PM

I hope my wind questions are not wearing on the list. I am trying to
interpret section 6.5.7 Topographic Effects.

Mean Height exceeds least horiz dimension therefore use Method 2.

Considering a 20' square by 35 foot tall enclosed structure located about
50' downhill from a relatively level area (escarpment)at the top of a hill.
The downhill slope is about 3 to 1 and is generally open grasses for an area
about 200 feet wide and about 800 feet down the hill. Surrounding this open
area are dense tall redwood trees. I do not know the topography at the
bottom of the hill beyond the redwoods, however the slope does continued
down into the forested area, but where it levels off I do not know.

I am confused by items 1 and 2 of section 6.5.7.1

Is the hill considered to be obstructed by the large trees on the sides of
the open area and 800 feet down the hill?
How do I determine H and Ln?
At what point is the hill no longer a hill?

From a first pass I get ranges of Kzt of 2.54 for a 2 diminesional ridge,
1.85 for a 2-D escarpment. But if section 6.5.7.1 does not apply it would be
1.0.

Happy New Year.

Jeff

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