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RE: What Exposure to use?

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Thank you,
I generally go to the building official to make this decision as he is the
person to determine the basic wind speed for his region. Exposure C is
defined as "terrain that is flat and generally open, extending 1/2 mile or
more from the site in any full quadrant." While this seems most reasonable,
Exposure D is defined as "represents the most severe exposure in areas with
basic wind speeds of 80 mph or greater AND has terrain that is flat and
unobstructed facing large bodies of water over 1 mile or more in width
relative to any quadrant of the building site..."
The wind speed for this region is 80-mph. While Exposure C appears to fit
the bill, I can't help but wonder in a region as exposed to wind gusts and
unobstructed flat lands for more than 1 mile if the definition of land
adjacent to water intended the definition to mean an area unobstructed by
"any kind of obstruction) which is generally the case where water exists
(unless it floats).

I guess I'm reading too much into this, but in nearly 15-years of practice,
I have yet to meet a building official that did not either pass out a sheet
listing the minimum wind design criteria for his region or to be able to
advise it by phone. This was a first for me.

Dennis

> -----Original Message-----
> From: Todd Hill [mailto:thill(--nospam--at)tkarch.com]
> Sent: Tuesday, June 12, 2001 3:09 PM
> To: 'seaint(--nospam--at)seaint.org'
> Subject: RE: What Exposure to use?
>
>
> I would use Exposure C.
> Why would you use D, you are located in the desert, correct?
> I've never had a building official give me the exposure.
> Exposure should be determined from our engineering judgment.
>
> -----Original Message-----
> From: Structuralist [mailto:dennis.wish(--nospam--at)gte.net]
> Sent: Tuesday, June 12, 2001 4:54 PM
> To: SEAINT Listservice
> Subject: What Exposure to use?
>
>
> This is the first time that I have had this one happen. I called
> the city of
> Indio California to obtain the local wind load design criteria. I was told
> that to use an 80-mph wind, but when I asked what exposure to use, the
> Building Official responded with - "Your the engineer, you determine that!
> Use a minimum of at least Exposure C."
> There is quite a difference between Exposure C and D which has me worried.
> The sign is a 25'-0" tall pole with a 60-s.f. (6'-0" high x 10'-0" wide)
> sign. The sign occurs in a windy off the freeway, however, the freeway is
> lined with trees intending to create a wind break. This prevents sand from
> blowing over and building up on the freeway.
> How can an engineer determine the specific wind load conditions for a very
> specific site if the building official will not provide the information?
>
> Any suggestions? The sign is for an Auto Body Repair store located on the
> road running parallel to the freeway. The area is open with industrial
> buildings close by, but the area is open for miles.
>
> Regards,
> Dennis S. Wish, PE
> Structural Engineering Consultant
> mailto:structures(--nospam--at)engineer.com
> (208) 361-5447 E-Fax
>
>
>
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