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Re: What Exposure to use?

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Dennis,

I've had just the opposite experience.  Very few of the building
officials I've met really understand the exposures, or the wind
speeds.  The guy in my home town told me to use 100 mph,
exposure C winds no matter where it is at!  I happen to know
that neither case is correct.

In your case, if your not next to a body of water, use exposure C.
If your not comfortable with your design, use a higher wind speed.
You could check the local weather records.  Remember that they
are likely reporting a 3-second gust, instead of fastest mile.

Dan Goodrich, P.E.


----- Original Message -----
From: "Structuralist" <dennis.wish(--nospam--at)gte.net>
To: <seaint(--nospam--at)seaint.org>
Sent: Tuesday, June 12, 2001 4:23 PM
Subject: RE: What Exposure to use?


> 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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