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# Re: IBC 2007 Wind calcs. - 2007 CBC load combinations

• To: <seaint(--nospam--at)seaint.org>
• Subject: Re: IBC 2007 Wind calcs. - 2007 CBC load combinations
• From: Neil Moore <nma(--nospam--at)omsoft.com>
• Date: Thu, 14 Feb 2008 16:47:13 -0800

One thing we should be looking at is the load combinations:

In Section 1605.3.1, you cannot increase the allowable stresses.  Does this mean that we would have to de-rate the shear wall values we've been using?

In Section 1605.3.2, you can increase the allowable stresses, but you will note that you have to increase the wind by a factor of 1.3, which might mean that we can you the shear wall values as written.

Hope I haven't missed anything?

For those of you who are struggling, our local SAGE structural group has started holding weekly noon-hour meetings (with the El Dorado County building officials) to sort all this transition problems out.  One of ex-presidents brought the pizza last week.

Neil Moore, SE, SECB

At 09:48 AM 2/14/2008, you wrote:
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(--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 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(--nospam--at)SE-Solutions.net
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, 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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