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Re: AISC Seismic Provisions (WAS Seismic bracing system- Knee-braced Frames)

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Is it still true that the entire AISC "Seismic Provisions" package is only
applicable to buildings, unless invoked by something outside of AISC?

And that AISC is silent in terms of applicability of any/all seismic
provisions applied to steel structure "Components" (IBC 1621) and
"Non-building Structures" (IBC 1622)?

While the current NEHRP Provisions seem to close most or all of the gaps in
applicability for steel structures, I am not aware of anything in the world
of the UBC and IBC that does.  It seems that non-building industrial
facilities, for example, if designed under UBC/IBC, are exempt from the AISC
Seismic Provisions.  For essential and hazardous facilities especially, this
seems like a very vulnerable loophole...

Mark D. Anderson  PE
Anchorage

----- Original Message -----
From: "Keith Fix" <kefix(--nospam--at)yahoo.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Friday, December 06, 2002 10:57 AM
Subject: RE: Seismic bracing system- Knee-braced Frames


> I think you're right, except maybe the answer doesn't lie with AISC, so to
> speak, but with the research community.  Somebody needs to put these
braces to
> the test and see what happens.
>
> The best argement for the knee-brace is the reliability of the connections
> themselves.  The questionability seems to lie in the system.
>
> Either way, without testing, we're stuck.
>
> All that said, where should the ductility be developed?  By ductility in
the
> brace, or by ductile hinge formation in the beam at the brace connection?
>
> -Keith Fix, PE
> -Little Rock, AR
>
> --- Igor Marinovic <IMarinovic(--nospam--at)vp.com> wrote:
> > I think that previous discussion about KBF systems omitted several
important
> > facts:
> >
> > 1) Typical KBF system used by PEMB industry is intended for small loads.
It
> > doesn't work, i.e., it becomes uneconomical, when the eave height
exceeds say
> > 20 ft. (even less than that)
> > 2) Typical KBF system used by PEMB industry does not carry gravity
loads,
> > other than selfweight.
> > 3) Typical KBF system has a brace located not far from the
beam-to-column
> > joint. Consequently, the KBF system behaves similar to moment frames,
where
> > the "triangle" at the top of the column transfers the moment across the
> > joint. The shape of the deflected members and the actual deflections are
> > almost identical to moment frames. However, the integrity of this system
> > relies heavily on three details: beam-to-column connection, brace
connection
> > to the column/beam, and brace strength for axial compression (and
tension)
> > loads. So, these would be the details subject to additional seismic
criteria.
> >
> > 4) If the brace is lowered so it connects in the middle of the column
height
> > the behavior of the system under lateral loads resembles the K-braced
CBF,
> > which, as mentioned by others, may have detrimental effects on the
column
> > (frame) integrity. This is not the Knee-braced system!
> >
> > So, lets recognize that in addition to apples and oranges, there are
pears...
> > The KBF system is a practical system that can be correctly designed and
> > detailed within certain height/load limits.
> > Maybe we need Charlie to suggest another category for the next version
of
> > Seismic Provisions. Maybe to add a subset to OMF category, with special
> > detailing requirements for KBF details mentioned above?
> >
> > Thanks,
> >
> > Igor Marinovic, PE, Memphis, TN
> >
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