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FW: Gusset Weld at Brace Connection

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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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