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RE: 2000 IBC v 1997 UBC code question

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Chuck and Jeff:

I also understand that the factors for wood are based on the load duration.
I have been told that this is also the case for other materials.  Then again
I have heard it argued on this list-server that that the 1/3 is only for
cases where multiple loads apply to account for the fact that max dead, live
and wind are unlikely to occur at the same time.  Sort of a simplified
probability analysis.  What ever the history though on the Left Coast we now
take the 1/3 on everything even seismic only load cases.  Do we have to
change our ways?

George Richards, P. E.
 
-----Original Message-----
From: chuckuc [mailto:chuckuc(--nospam--at)pacbell.net]
Sent: Monday, October 29, 2001 1:35 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: 2000 IBC v 1999 UBC code question


Jeff-
My understanding is slightly different regarding wood.  I thought the 1/3
increase for wood had to do with the fact that wood's test capacity is
highly
rate dependent.  The 1/3 increase is used for dynamic loads like seismic.
The Simpson values should come from tests in wood, and would therefore by
allowed the increase--however, I'm not sure that is in fact how they test.
I'd
bet a nickel that the very close nail spacing on some of their straps would
split the grain.  I don't think ICBO does a very good job of monitoring the
test
setups used (and or permits dubious calculation methods to be used to derive
the
loads ratings for some hardware).
Chuck Utzman, P.E.

Jeff Barrett wrote:

> George:
>
> To answer your question...it is my understanding that the 1/3 stress
> increase never had experimental data to back it up.  It simply was "always
> done that way".  Now, the IBC has taken that option out even though the
> individual referenced standards allow it (AISC, ACI, etc...)  Wood is
still
> allowed because it is unlike the other materials because in its design
> criteria the allowable stresses are low and then bumped "up" by factors
such
> as 1.15 and 1.6 depending on the criteria.  This is due to the fact that
> every wood member is different.  Other materials such as steel start with
> higher stresses (because of the better quality control of the material)
and
> are reduced.
>
> To answer your question regarding the Simpson ties...you better ask them,
> but my feeling is most of those connectors are governed by the connection
> (nails, screws, etc...) and the failure is in the connection to the wood.
> Consequently, for wood connections, these Simpson would not need to be
> reduced since the stress increase is allowed for wood.  However, if you
were
> using these connectors in light gauge steel design, they would have to be
> reduced.
>
> Jeff
>
> ----- Original Message -----
> From: "George Richards P.E." <george(--nospam--at)borm.com>
> To: <seaint(--nospam--at)seaint.org>
> Sent: Monday, October 29, 2001 1:51 PM
> Subject: 2000 IBC v 1999 UBC code question
>
> > Fellow Engineers:
> >
> > I am reviewing the impact the IBC will have on how we design out West.
> >
> > Using 1997 UBC Alternate Basic Load Combination 1612.3.2 we are allowed
a
> > 1/3 stress increase for wind or seismic only loading regardless of if
the
> > material is wood, steel, or concrete.
> >
> > Using 2000 Alternate Basic Load Combination 1605.3.2 we are NO LONGER
> > allowed a 1/3 stress increase for wind or seismic only unless
specifically
> > given in the material section.  This means wood only.
> >
> > First question:  Did I read this correctly?
> >
> > Second question, {mostly for those of you in Texas where I know that
every
> > home is Engineered :)} where the IBC has been adopted are you still
using
> > Simpson numbers or since they have also included a 1/3 increase on steel
> are
> > you down grading them?
> >
> > Thanks in advance.
> >
> > George Richards, P. E.
> >
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