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RE: wind load on 2 sided structure

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If I am not making mistake, this type of condition has been proposed in
ASCE -05. If you know any committee member, he may help you for the net
pressure coefficent to be used.

Himat

>>> BSBossley(--nospam--at)venturaengineering.com 1/7/2005 9:01:07 AM >>>
Thanks to everyone who responded to my post.  I've already come up
with
my conclusion, which has less to do with the wind loads than with the
fact that the structure has a standing seam roof on it which can't be
assumed to act as a diphragm. But, I was hoping someone knew about
this
for future reference.

The wind loads I used were calculated by assuming the two walls will
act
like signs because I'm pretty sure that you couldn't develop any
internal pressure, so then it's a question of whether to use 1.2(sign)
or 1.3(building) for lateral load. I went with the latter of the two,
but my real question was really more about how you would handle the
roof
wind load increase. And what roof load would be applicable.  I agree
that the partially enclosed model gives you the worst results, and I
checked it against that, though I did not include the internal
pressure.

Brian S. Bossley, PE
Ventura Engineering
7610 Olentangy River Rd.
Columbus, OH 43235
(614) 847-1110 x121


 

________________________________

From: akester [mailto:akester(--nospam--at)cfl.rr.com] 
Sent: Friday, January 07, 2005 1:01 AM
To: seaint(--nospam--at)seaint.org 
Subject: wind load on 2 sided structure


I have always thought you cannot go wrong with a partially enclosed
model. If it is fuzzy and doesn't quite meet the definitions, I
believe
this will always give you the highest values. Now I don't have ASCE in
front of me, but 2000 IBC has a little formula in 1609.2 for partially
enclosed. Open means each wall is 80% open, like someone else said.
 
 I think about it this way. Any amount of wall you put up will block
the
wind, and send it upwards to your ceiling or U/S of the roof, and
around
the wall. One entire solid wall still will direct a lot of wind up and
against the roof. But if you have two adjacent solid walls and that
gets
hit by wind at a 45 degree angle, and the walls go all the way up to
the
roof, there is not much open wall area for the pressure to be
relieved,
it just keeps building up and some escapes around the edges. 3 walls
and
one open end is like holding a paper grocery bag in front of a large
fan, the pressure is going to be high on all the surfaces...  I have
seen plenty of pics and heard plenty of stories of wind blowing out a
garage door then taking the roof out.
 
Now, I am mainly thinking about C + C loads. I suppose if you were
designing things for shear, or uplift at the foundations, you may
tweak
your model a bit. But I like to be conservative with C + C loads, as
well as with structures that don't fit code models well. But why
bother
splitting hairs, a small increase in wind pressure does not seem to
have
a huge impact on the design and cost of most low rise buildings (in my
experience). Not for the peace of mind at least. You still need roof
connections, tie downs, bars at 48" o.c., screw down the deck, etc.
 
HTH,
Andrew Kester, PE
Lake Mary, FL

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