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FW: FW: FW: Reinforcement detailing in coupling beam

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Frank:

As far as what will happen to the steel columns and the coupling beams
during the design earthquake, the important thing to look at is the CAPACITY
of each of the competing members.  Given that you will have a 60" deep
coupling beam, vs a WF10, it would appear that the coupling beam will
control and the columns will be yielding.

Think of it this way - the cb will have constant moment (even though shear
action dominates, it will still have to manifest flexure since flexural
deformations will occur) equal to the moment at mechanism formation - since
the beam is so deep, the moment will likely be large, and the steel columns
will cause a little blip at the midspan of the cb but not lare enough to
change anything.

That said, I think that the column is going to give you some heartburn, but
more from a detailing perspective than anything else.  I have found that 24"
wide coupling beams with diagonal struts work pretty well detailing-wise,
18" wide are doable, but anything else just gets too hairy for the actual
field work involved in constructing the beam because of the intersection of
the two struts at midspan.  There needs to be a certain amount of room to
allow the struts to pass each other, and if there is a colum in the way at
midspan I would say you are likely to have some problems.

So, I can see two ways of approaching this situation:

1)  As suggested previously, see if you can make the system work by assuming
NO coupling action between the walls.  If the 2 separate cantilever walls
work OK, then don't even think twice about coupling the walls - just give
youself a nice sturdy foundation element, OR you could go to the foundation
and install a hefty coupling footing (with essentially beam reinforcement)
to get some nice fixity there.

2)  If coupling is essential, then I would probably try and reframe the
floor so that the column at the middle could come out.  I don't know
anything about your floor framing, but it seems logical to conclude that the
offending column is being framed into by way of girders running
perpendicular to the new walls.  How about putting in TWO columns, one on
both sides of the walls just outside of the wall faces?  The presence of a
continuous girder running just below the floor above through the coupling
beam shouldn't present a problem since this will be at the point where the
diagonal struts are at mid-depth of the cb.  Install the two new columns,
cut out the old column, THEN install the walls and coupling beams unimpeded.
OR, even better, if the walls are at the exterior face of the building, then
just install a new column outside the wall face and get rid of the column in
a similar manner.

Let me know if this gets you going in the right direction.

Regards,

T. Eric R. Gillham PE
PO Box 3207 Agana Guam 96932
Ph: (671) 477-9224
Fax: (671) 477-3456
Pgr: 720-8891
eric(--nospam--at)gk2guam.com <mailto:eric(--nospam--at)gk2guam.com>


-----Original Message-----
From: Fariborz Tehrani [mailto:fmtehrani(--nospam--at)yahoo.com]
Sent: Sunday, October 28, 2001 5:07 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: FW: FW: Reinforcement detailing in coupling beam


Eric,
Thanks a lot for these helpful information. Now I'm
getting a better idea myself about the essential facts
in this situation.
I'm dealing with an existing steel structure
strengthen by new concrete shear wall. So I don't want
to touch the old steel system, simply because that the
situation will get more complicated and would involve
steel beams and etc.
However having the column at the middle, would make
the coupling beam span shorter in reality, means that
shear action will dominate for sure. Is this right?
The typical span and depth for coupling beam is 15'
and 5' respectively and steel columns and beams are
WF10.
If this assumption would be right, it seems that I
might be able to have two coupling beam transferring
their shear load to the column at the middle.
On the other hand, I came to this idea from your
comments that it might be better to just make the
steel beam to act like coupling beam and ingnore
diagonal rebars.
Thanks again,
Frank


--- "T. Eric Gillham PE" <teric(--nospam--at)gk2guam.com> wrote:
>
>
> -----Original Message-----
> From: T. Eric Gillham PE [mailto:teric(--nospam--at)gk2guam.com]
> Sent: Saturday, October 27, 2001 11:34 AM
> To: seaoc list
> Subject: FW: FW: Reinforcement detailing in coupling
> beam
>
>
>
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