Structural Engineering: RE: IBC 2007 Wind calcs.

There is a BIG difference between being "not as easy as the UBC" and being
complex enough that it is tough to use. I think that both Chris' and my
point is that we don't disagree that it is more complex than the UBC, but it
is also not hard to use (in our opinion).

Personally, I don't know how much of the grumbling is due to 1) people not
liking change; 2) people just not being used to it and have to adjust to it;
or 3) people just not understanding it because it is too "complex" for them.
I suspect that a lot of it is #1 and #2 and that once people get past those
two issues (which time will solve), that #3 is really a non-issue.

Regards,

Scott
Adrian, MI

-----Original Message-----
From: Haan, Scott M POA [mailto:Scott.M.Haan@usace.army.mil]
Sent: Thursday, February 14, 2008 7:03 PM
To: seaint@seaint.org
Subject: RE: IBC 2007 Wind calcs.

If you read the guide - I think per ASCE 7-05 6.1.4.1 you are supposed to
use a minimum of 10 psf projected on the vertical surface when you have no
horizontal pressure component on the roof. I rest my case: not as easy as
the UBC.

-----Original Message-----
From: chris.slater@gmail.com [mailto:chris.slater@gmail.com] On Behalf Of
Chris Slater
Sent: Thursday, February 14, 2008 2:46 PM
To: seaint@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@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@umich.edu]
> Sent: Thursday, February 14, 2008 9:58 AM
> To: seaint@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
> Adrian, MI
>
> -----Original Message-----
> From: Matthew [mailto:sandman21@gmail.com]
> Sent: Thursday, February 14, 2008 12:48 PM
> To: seaint@seaint.org
> Subject: Re: IBC 2007 Wind calcs.
>
>
> You can also try using
>
> http://www.documents.dgs.ca.gov/dsa/pubs/IR-16-7_WindLoad_12-18-07.pdf
>
> Matthew
>
>
> On Thu, Feb 14, 2008 at 9:34 AM, Paul Feather
> <PFeather@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
> simplify your life,
> 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@SE-Solutions.net
>

www.SE-Solutions.net <http://www.se-solutions.net/>
>
>
>
> -----Original Message-----
> From: sscholl2@juno.com [mailto:sscholl2@juno.com]
>
> Sent: Thursday, February 14, 2008 9:09 AM
> To: seaint@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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