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RE: wind loads make me crazy

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Lots of times, doors and windows are assumed to be designed "per code" and therefore are not assumed to be "openings".  I know that sometimes this assumption is made solely on the fact that the building is designed "per code" and therefore the windows and doors should be designed "per code".   I used to work for a metal building company and I was concerned that this issue may not be addressed fully on each project and therefore, maybe we shouldn't assume the windows and doors are designed per code.  Possibly, the EOR can specify that the doors and windows be designed for the code prescribed wind forces and therefore they are not "openings".  Are door and windows designed for the code prescribed wind forces on each project?  I think not.

Any building which may be required to function in a windstorm (such as a fire station) should be designed assuming the worst case of enclosed or open.  And what about an airplane hanger?  Maybe I'll avoid liability if I just add a note to my drawings that the hanger doors are to be closed when the wind blows.  (I'm just kidding about that, so please don't attack me!)  Just something to think about.

I went to an ASCE 7 wind seminar in KC MO a few years ago and I remember Dale Perry and Kishor Mehta showing pictures of metal building failures that were initiated by wind failing large overhead doors and then the building behaved as a partially enclosed building and the wind blew some roof and wall panels off at the corners of the buildings.  

Also, depending on your location and the building design, the windows may need to be missile impact resistant.  ASCE 7 has info on this subject.

Bruce D. Holcomb, PE
Butler, Rosenbury & Partners
300 S. Jefferson, Suite 505
Springfield, MO 65806-2217
ph (417) 865-6100
fax (417) 865-6102





-----Original Message-----
From: Andrew D. Kester [mailto:andrew(--nospam--at)baeonline.com]
Sent: Thursday, March 20, 2003 7:47 AM
To: seaint(--nospam--at)seaint.org
Subject: wind loads make me crazy




Please, can someone save our sanity.

I have looked at old posts from the list  and some people have came to the
same conclusions as me, but I just want to make sure.

After careful examination of the FBC, ASCE, etc. and their definitions of
building classifications, things still seem a bit cloudy. Pardon
paraphrasing or typos.

Enclosed- nothing below
Open- All walls at least 80% open. This is pretty straightforward.
Partially Enclosed:
Area of openings in wall is greater then all of the other opening areas by
10%
AND
Area of said openings > 4sf or 1%, and the % of openings in the rest of the
building do not exceed 20%.

OK, so someone used the analogy of a bag, open at one end, with holes cut in
the rest of the bag greater then the opening plus 10%. So the wind goes in
the large opening, and can go out the other openings. I can buy that. So if
that is the case, but not all the walls are 80% open , it is enclosed? I
guess this defies logic because it is classified as "Enclosed" whether it
has openings or not. But what ASCE is really saying is you model it as an
ENCLOSED building when there are enough openings to relieve the pressure,
because the actual pressures will proximate those of an enclosed building. I
guess the whole thing is an ENCLOSED building, or a building with lots of
openings (but not OPEN), have very similar wind loading pressures.

Now the problem is we have a rectangular metal building with several large
openings. At each short end the walls are almost completely open, and the
long ends there are a series of openings but not 80%. It does not meet the
definitions of Partially Enclosed either. So despite numerous large
openings, strictly by code , it should be designed using ENCLOSED loads. (
However, if I were designing this, I would do the worse case of ENCLOSED and
PARTIALLY ENCLOSED. But we are the EOR and this is a pre eng MB.)

Some confirmation would do wonders to our mental health, as we thought we
finally had this wind loading thing under control.

Might I add in reading in the ASCE, any building not meeting ASCE or other
Code definitions, may be designed using coefficients from "Technical
Literature", as given in Table 1.4.1 of the "Guide to the use of the wind
load provisions of ASCE 7-98". One book listed in "Wind Effects on buildings
and structures", which I recently bought off the internet. The back is
chocked full of tables and charts I have never seen in other refs. The book
itself is quite complete in wind design and I have only grazed the surface.
I guess all these tables are from "smooth flow" wind tunnel tests the ASCE
did back in the 60s? So use the coefficients with caution. But I find them
to be a good supplement to current ASCE provisions, and the tables alone
were worth the price of the book...


TIA for input!


Andrew D. Kester, EI
Structural Engineer
Bentley Architects & Engineers
665 W. Warren Ave.
Longwood, FL 32750
1-407-331-6116
andrew(--nospam--at)baeonline.com
www.baeonline.com




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