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RE: Eccentrically Braced Frame - Link Beam

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Oshin,

The beam should have basically the full inelastice response in terms of
strength available to it even if it has seen some inelastic behaviour in
the past.  The one possible exception to this would be if the beam had
been exposed to enough inelastic loading that it was completely damaged
such that the inelastic mechanism was no longer able to form correctly
(i.e. the stiffners had been put through so much that the welds connecting
them to the beam had fractured or pieces of the beam itself had
fractured), which does not seem to be the case in you situation.

Now, where you may not have as much "latitude" would be in the area of
lateral displacement.  If the system has gone inelastic, then you will
have some permanent deformation in the system that cannot be "recaptured"
with out major repairs/replacements.  This means that you will likely have
less inelastic displacement available for "use" in the next seismic event.
This also means that you have less available inelastic deformation
available (aka energy dissipation) before you reach ultimate.  So, while
you can still reach the same loading, the member will be closer to
reaching the point at which enough inelastic deformation occurs to finally
reach the ultimate point and the member truly fails (i.e. fractures,
crushes, etc).

The point is that as long as a structural members has not reached ultimate
capacity (i.e. fractured, crushed, truly failed, etc) and is only gone
into the inelastic range, it should be able to still handle the same
inelastic load.  Just think back to you simple stress-strain curves.  Even
in the inelastic range, the response will go back down to zero stress when
unloaded following a line parallel to the elastic line that goes up (with
slope of E), but you will not hit the strain at zero...there will be some
permanent deformation.  You can still reload the member (following that
same parallel elastic line) up to the inelasitc level.

HTH,

Scott
Ypsilanti, MI


On Wed, 11 Sep 2002, Oshin Tosounian wrote:

> Chung-Soo,
>
> Thanks for your reply.
>
> What I have described in my original post is a real building, not an
> experiment, that has sustained real earthquake damage. The question is do we
> need to replace the link beams given the fact that some yielding may have
> occurred? Would you even consider strengthening the link beams given the
> fact that significant post yield capacity still exists? How does minor
> yielding in the link beam affect the future performance of the frame?
>
> Regards,
>
> Oshin Tosounian, S.E.
> Los Angeles
>
> > -----Original Message-----
> > From: Chung-Soo Doo [mailto:CDoo(--nospam--at)sdesf.com]
> > Sent: Wednesday, September 11, 2002 4:00 PM
> > To: seaint(--nospam--at)seaint.org
> > Subject: Re: Eccentrically Braced Frame - Link Beam
> >
> >
> > In your description, what is an earthquake? Does it mean the
> > loading history
> > shown in AISC seismic provision or FEMA?
> >
> > The web stiffeners in the link provide the stiffness against
> > the web local
> > buckling and protect the sudden degradation of capacity after
> > ultimate state.
> >
> > If the earthquake force is small, of course, minor yielding
> > occurs. However,
> > you need to finish your test until it fails or up to the
> > certain strength
> > degradation.
> >
> > Chung-Soo Doo
> >
>
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