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Re: Reinforcement detailing in coupling beam

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Eric,
I checked some of your ideas. Moving columns outside
of opening cannot be done. Because I have to push them
far enough from wall face to provide develop length
for diagonal rebars. Am I right?
So it seems that changing the design to cantilever
walls would be more practical. Also having the new
wall few inches offset from the columns line might be
another solution.
Thanks,
Frank



--- "T. Eric Gillham PE" <teric(--nospam--at)gk2guam.com> wrote:
> 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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=====
Fariborz Tehrani,                      Phone: (310)801-4237
Civil Engineer                           Fax: (530)481-9532
BSCE, MSCE, PE                    Voice Mail: (877)743-6206
email: fmtehrani(--nospam--at)msn.com
web: www.fmtehrani.com

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