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Re: Causes of a "fatal flaw?"

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Chris,

Knowing Ralph Richard personally, and having listened to his explanations on
a number of occasions, it took me a long while to figure out what he was
saying.  Without either endorsing or criticizing his solution, I will see if
I can explain what I believe he is saying.

When the beam is subject to moment at the connection, it is trying to curve
and the *web* produces radial tension and compression stresses on the
flanges, normal to the plane of the flange.  The curvature of a beam due to a
negative moment will cause the web to have high compressive stresses on the
top flange, and high tension flanges on the bottom flange.  The web is trying
to prevent the top flange from crushing the web, and trying to prevent the
bottom flange from straightening out.  This affect of the web puts a high
shear [his prying action] in the *flange-to-column connection* in addition to
the tension/compression force in the plane of the flange.  The resultant
force, which is much higher than the force the weld is designed for, and is,
he theorizes, the cause of the moment frame failures.

The solution, according to Ralph Richard and his partners, is to slot the web
at its junction with the flange so that these compression and tension forces
normal to the plane of the flange cannot develop at the beam to column
connection.  This way, the high shear forces in the flange due to the radial
stresses from the flange cannot develop, and therefore the high resultant
force is not developed.  The web to column connection will still carry the
beam shear.

Hope this helps.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Chris Wright wrote:

>Two studies published at
>http://www.muckraker.org/investigations/steelhome.html attempt to
>explain the fundamental causes of the failure of the "pre-Northridge
>connection.

I've got some real problems with this web site. First, the site explains
nothing and proves nothing. Consider the statement
>  'testing and finite-element analysis led to the discovery of
> the cause of the prying action mentioned in the paper. As
> the beam is flexed, one side of the beam's flange contains a
> large compressive stress component while the other side of
> the same flange contains a large tensile stress component. The
> result is often the separation of the beam flange from the
> column flange in the form of a weld or flange fracture or
> a column flange divot, which was often seen during building
> inspections following the Jan. 1994 Northridge earthquake, said
> Richard.'
It's only a restatement of the obvious, pretending to be some wondrous
discovery. The gap between '...large tensile stress component.' and  'The
result is often the separation...' is arm-waving. Not even Indiana Jones would
make such a leap of faith.

The discussion of brittle fracture is tripe. So is the following:
> The story of engineering drama was recently published in Structural
> Engineering magazine. While this publication's target
> audience is 30,000 licensed professionals, the article's essence
> is easily understood by non-engineers.
If it were so easily understood, the author wouldn't have gotten it so far
wrong.

Second, the phrase
> 'Richard is co-owner and inventor of SSDA's  proprietary SlottedWeb_
> seismic connection design, which competes with the
> now popular reduced beam section (RBS) connection as  proposed
> in FEMA's study.'
shows clearly that the studies are meant to flog an invention, not provide
useful information.

I don't doubt that those connections had serious problems and I suspect I know
what happened, but the web site is technical and professional dreck.

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