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# RE: IBC 2007 Wind calcs.

• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: IBC 2007 Wind calcs.
• From: "Scott Maxwell" <smaxwell(--nospam--at)umich.edu>
• Date: Thu, 14 Feb 2008 19:22:33 -0500

```Nope.  You are not missing a thing that I can see.  If I do use method 1,
then I tend to do something rather similar.

That is why I don't find Method 1 that complicated.  And I don't even need
to use a program to get the pressures (the "toughest" thing of the whole
process is to have to interpolate off the chart).

Regards,

Scott

-----Original Message-----
From: chris.slater(--nospam--at)gmail.com [mailto:chris.slater(--nospam--at)gmail.com] On Behalf Of
Chris Slater
Sent: Thursday, February 14, 2008 6:46 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: IBC 2007 Wind calcs.

All of this talk is making me worry that we're doing something horribly
wrong...

I put up a sample of the way we're doing our wind calcs here:
http://www.examplecalcs.com/hosted/18329.pdf

I use a program to generate the A, B, C and D loads.   If the B and D
loads are negative, I just use 0.  Then I generate my wind loads by taking
the B pressure from the ridge down to the plate, and the A
pressure from the plate to the middle of the wall height.   In the
example I posted, W1 and W2 are calculated that way.

For gable ends, or lower levels, I just use the A load from the top of the
projected area to the middle of the lower wall, which is how I got W3 and W4
in the example.

For long buildings, I will sometimes use the C and D loads for the section
of the building that is more than 2a from the corners, but in general, I
just use the A and B loads since these tend to be lower than the projected
area winds we used in the old UBC code.

It's not simple, but it's not incredibly complicated either.  Which makes me
worried.  Am I missing something, or does this seem like a reasonable
approach.

Chris

On Thu, Feb 14, 2008 at 2:58 PM, Haan, Scott M POA
<Scott.M.Haan(--nospam--at)usace.army.mil> wrote:
> Scott.
>
>  Compared to the UBC, all the ASCE 7 methods are more complicated.  I
> agree  with people who said use the analytical method for a rigid
> building is the  easiest way because there aren't 10 different zones
> etc... etc... but you  still have to have a spreadsheet to calculate
> the pressures.
>
>  I think if I had to design a flexible building I would send chocolate
> cupcakes with turds in the middle to the ASCE7 wind committee have a
> supercomputer to calculate the gust factor.
>
>  Scott.
>
>
>  -----Original Message-----
>  From: Scott Maxwell [mailto:smaxwell(--nospam--at)umich.edu]
>  Sent: Thursday, February 14, 2008 9:58 AM
>  To: seaint(--nospam--at)seaint.org
>
>
> Subject: RE: IBC 2007 Wind calcs.
>
>  I want to say that this method is more or less based off the
> simplified  method that Washington has produce and has been mentioned
> by others.
>
>  Personally, while I find there to be some complexities that I don't
> feel are  necessarily needed in the current ASCE 7 wind provisions, I
> don't find them  that difficult to use...including Method 1.  I find
> that I can pump out wind  pressures in method 1 in very short order.
> It does take more time to use  those pressures to analyze stuff in
> MWFRS since they now have corner  pressures and such...but you don't
> really gain that much compared to older  more "uniform" pressures
> except for some buildings that might be rather  succeptible to
> torsional effects.  But it does help that I have been using  the ASCE
> 7 methods for a LONG time, while engineers in CA are more used to
> only using the simplified methods that were in the UBC.
>
>  I would be the first to agree that ASCE 7 has gone of the deep end to
> some  degree in "sharpening the pencil" for wind provisions, but I am
> not sure that  I would liken them to a doctoral thesis (unless you are
> talking about the  wind provisions for signs or flexible structures or
> dynamically sensitive  structures and have to start calculating gust
> coefficients).
>
>  Regards,
>
>  Scott
>
>         -----Original Message-----
>         From: Matthew [mailto:sandman21(--nospam--at)gmail.com]
>         Sent: Thursday, February 14, 2008 12:48 PM
>         To: seaint(--nospam--at)seaint.org
>         Subject: Re: IBC 2007 Wind calcs.
>
>
>         You can also try using
>
>         Matthew
>
>
>         On Thu, Feb 14, 2008 at 9:34 AM, Paul Feather
> <PFeather(--nospam--at)se-solutions.net> wrote:
>
>
>                 Stan,
>
>                 First off, the simplified method is anything but
> simple.  We  use the
>                 general method (method 2) for everything and get more
> consistent results
>                 easier.  The simplified method is derived from metal
building
>                 manufacturer methods, and for anything but a metal
> building  results in a
>                 complete book keeping atrocity.
>
>                 You are looking at 25 degrees area B.  The way the
> simplified  method
>                 works this is just one small area that cannot be
> applied in  the same
>                 thinking as the UBC horizontal projected area.  You
> have to  add the area
>                 B to the Area E uplift, basically all areas A through
> H get  applied
>                 simultaneously as one load case.  Then you rotate the
> building reference
>                 corner and apply the whole thing again for all four
> reference  corners.
>
>                 Get away from the simplified methods and you will
>                 while getting something closer to what you are used
> to.  I  don't believe
>                 the ASCE wind provisions could be any more convoluted
> and  difficult to
>                 apply to real world engineering if we tried.  The UBC
> methods  were
>                 derived as a conservative simplification of the ASCE
> provisions years
>                 ago, and we desperately need to achieve something
> similar  again.
>                 Spending three days on a doctoral thesis to develop
> simple  wind
>                 pressures as opposed to working on load path and
> quality  engineering is
>                 counter-productive, and saving 1.4 psf in wind
> pressure only  matters to
>                 mass produced square boxes trying to be paper thin.
>
>                 Paul Feather PE, SE
>                 pfeather(--nospam--at)SE-Solutions.net
>                 www.SE-Solutions.net <http://www.se-solutions.net/>
>
>
>
>                 -----Original Message-----
>                 From: sscholl2(--nospam--at)juno.com [mailto:sscholl2(--nospam--at)juno.com]
>
>                 Sent: Thursday, February 14, 2008 9:09 AM
>                 To: seaint(--nospam--at)seaint.org
>                 Subject: IBC 2007 Wind calcs.
>
>
>                 After 40 yrs. of doing UBC calcs. I am attempting to
> do my  first IBC
>                 calcs. and need help, even after attending a seminar,
> which  seemed to
>                 cover lots of things but not this.
>
>                 For a simple house, using 6.4 Method 1 Simplified
> Procedure,  I cannot
>                 get a reasonable wind pressure of something between 15
> psf  and 25 psf.
>
>                 From 6.4.2.1 <http://6.4.2.1/> , I get p s= 1.0 (1.0)
> 1.0
>
> (2.3) = 2.3 psf which is
>                 unrealistic. This is using Fig. 6-2, exposure B, h=30
> ft.,  Kzt =1
>                 and I=1
>
>                 Can someone point out my omissions/errors?
>
>                 Stan Scholl, P.E.
>                 Laguna Beach, CA
>
_____________________________________________________________
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>
>
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