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Re: Gusset Weld at Brace Connection

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Once again, thanks Charlie,

After all these years, just when (or was that whine) I think I've got
it..........

Anyway, your response was what I was looking for.

By the way, you were confused by one of my questions, which I answered
myself .  The 1.4 factor is applied to the larger of 1.4 x fave or fpeak
whichever is larger.  I finally found a paragraph explaining that in the
connections manual.

Thanks again,
Joseph R. Grill, PE


----- Original Message -----
From: "Carter, Charlie" <carter(--nospam--at)aisc.org>
To: <seaint(--nospam--at)seaint.org>
Sent: Thursday, January 02, 2003 8:45 AM
Subject: FW: Gusset Weld at Brace Connection


> Coincidentally, I was just getting the following response finalized for
you.
> It is based upon the work of my colleague here at AISC Chris Hewitt. The
> answers are below.
>
> Charlie
>
> ******************
> >Was this guys name Richard Whitmore
> >or were they two different people,
> >brothers or cousins?"
>
> Whitmore is R.E Whitmore who, as Emeritus Assistant Professor of Civil
> Engineering at the University of Tennessee, published Knoxville
Engineering
> Experiment Station Bulletin No. 16 in May of 1952 entitled "Experimental
> Investigation of Stresses in Gusset Plates".
>
> Richard is Ralph M. Richard, Emeritus Professor of Optical Sciences at the
> University of Arizona. That title fools me a bit in that I know of him as
a
> civil engineer and perhaps the world's leading expert in finite element
> analysis.
>
>     http://www.optics.arizona.edu/Faculty/Resumes/Richard.htm
>
> >Where did this 1.4 come from?
> >Is it the "Richard Factor" mentioned on
> >Page 7-123 and where did this Richard
> >factor come from?"
>
> The 1.4 factor (commonly referred to as the 'Richard' factor) is based on
> test results of finite element modeling conducted by Ralph Richard from
the
> University of Arizona. The paper was published in the Proceedings from the
> AISC Engineering Conference (now the North American Steel Construction
> Conference) in Nashville (Ref: Richard, Ralph M., (1986), "Analysis of
Large
> Bracing Connection Designs for Heavy Construction," Proceedings AISC
> National Engineering Conference, Nashville, June, pp. 31-1 through 31-24).
>
> Richard reported a peak stress of 1.4 times the average scalar stress on
the
> welded connection of the gusset to the beam or column flange. The factor
is
> applied to ensure that there is sufficient ductility such that the peak
> stress does not cause an unzipping of the weld at the location of the
stress
> concentration and a progressive failure of the welded connection. This is
> important to the theory of the uniform force method and the factor should
be
> applied to ensure ductility under any loading condition, not just in
seismic
> aplications.
>
> There is an AISC Engineering Journal paper in the works by Chris Hewitt
and
> Bill Thornton that will be published in the first or second quarter of
2003
> which will address this topic more thoroughly. It is also anticipated that
> the re-evaluation of the Richard data and recommendations will allow a
> reduction of the value used in design below 1.4. The current 1.4
> recommendation is based upon the peak value whereas the paper advocates
the
> use of a 90% statistical confidence interval, which is more consistent
with
> the formulation of the rest of the design methods and recommendations we
use
> every day.
>
> It should also be noted that a bolted connection or a welded connection to
a
> column or beam web is assumed to be flexible enough to redistribute the
> stresses without need for the 1.4 factor.
>
> >Also, if the ratio would have been greater
> >than 1.4 what would the author have done?"
>
> I'm not sure I understand your point. The experimental data indicated a
peak
> value of 1.4 and that was the basis of the recommendation. If it had been
> different, so would the recommendation, I suspect.
>
>
>
>
>
>
>
>
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