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Re: Eccentrically Braced Frame - Link Beam

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Oshin,

Sorry about the misunderstanding. Now, I think I understand better.

You have an EBF which experienced a certain degree of earthquake. For now, I
don't want to say "damaged".
The link beam seems to be experienced a certain degree of yielding cycle. So,
your question is if we need to repair it.

First of all, I am not good at retrofit. But if I have a situation like you, I
may solve the problem like following.

We know the link beam has enough deformation capacity without strength strength
degradation through several test results. However the test was performed within
the certain link beam rotation. That is why codes specify the link beam
rotational limit.

1. Measure the straightness of link beam.
    Check the unevenness of floor is within the acceptable range.
    if it is in the acceptable range
        Calculate the link beam rotation.
        Reduce the link beam rotation limit by the calculated rotation.
        if the rotation is smaller than the modified rotation limit
            Go to next checking
        if not
            Replace it.
    if not
        Replace it.
2. If the inspection in item 1 is passed, the link beam may be considered
"sound", and I would like to say the beam is "experienced beam". I can say the
beam can provide the strength and stiffness in the future earthquake.
3. If the inspection in item 1 is not passed, the beam can be considered
"damaged" and need to be replaced.

This is my rational to check this kind of situation. I wish my rational can help
you in solving the problem.

Chung-Soo




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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