Very good advice - and creative. Thanks Paul, I will consider this as
economy for this client is important. I am a neighbor of this client. His
work takes him all over Southern California and he has, in the past, sought
the help of engineers in other areas where the signs are to be located. He
would rather work with one engineer and being in the same town creates an
opportunity for me. However, if my designs are more conservative than he has
used, he will not be as competitive and this can easily affect his decision
to use my services. This is why it is necessary for me to obtain a value
that can be verified with the building official and then use my judgment to
either scale up or use the values provided.
This was also the motivation for the creation of the spreadsheet I just
donated to the Structuralist.Net. It took a bit of work - as an investment
in his future business - to create the spreadsheet to be used on each job.
The cost is amortized over at least a years worth of work to make the
initial high investment payback in a reasonable period of time.
For those who are interested, the Spreadsheet, which calculates up to three
individual signs on one pole can be found on the Structuralist.Net Software
productivity forum as well as a discussion of how to create the logic for
conditional statements to isolate that portion of each sign that lies within
range where wind loads change due to elevation changes. Your free to use it
and improve upon it. The spreadsheet only calculates the moment at the
bottom of the pole for design of the column and footing using another
software. I suppose I'll add this as it is not a difficult calculation and
post the update soon. Hope others find it useful, but please don't solicit
from my client:o)
Dennis S. Wish, PE
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> -----Original Message-----
> From: Paul Feather [mailto:pfeather(--nospam--at)san.rr.com]
> Sent: Tuesday, June 12, 2001 3:46 PM
> To: seaint(--nospam--at)seaint.org
> Subject: Re: What Exposure to use?
> Exposure D is clearly defined with regards to large open bodies of water.
> Large open bodies of sand where not considered by the code writers I am
> sure, and I can see your analogy. If you do not feel that the exposure C
> 80mph forces are appropriate, increase the wind speed. There are areas of
> Ontario along the 10 Freeway corridor that require exposure C 90mph as a
> minimum. I would definitely consider the 10 corridor as a special wind
> You have a lot of control over how you apply the designated wind
> requirements. If you use Exposure C 80mph, you don't have to take the
> stress range up to the maximum, you can limit deflection or stresses to
> within a range you are comfortable with. It is a question of economy and
> engineering judgment.
> Exposure D 80mph is only 25% more than Exposure C 80mph. From 80
> to 90 mph
> is 25%. A self mandated 25% reduction in allowable stresses achieves the
> same thing. Pick a level you are comfortable with.
> Paul Feather
> San Diego, CA
> ----- Original Message -----
> From: "Structuralist" <dennis.wish(--nospam--at)gte.net>
> To: "SEAINT Listservice" <seaint(--nospam--at)seaint.org>
> Sent: Tuesday, June 12, 2001 2:54 PM
> Subject: What Exposure to use?
> > This is the first time that I have had this one happen. I
> called the city
> > 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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