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Floating Column
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saahil
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Joined: 12 Aug 2011
Posts: 26

PostPosted: Thu Sep 29, 2011 7:40 am    Post subject: Floating Column Reply with quote

I am designing a G+13 building in etabs. The building has some of the
columns stubbed at 1st floor and the upper 12 floors are supported by
floating columns which are resting on beam at first floor lvl (please
see attached file). Two of the floating columns FC1 & FC2 having
different orientations are resting on the same beam.My problem is how
do I rest these floating columns (FC1 & FC2) on a single beam in etabs

Regards
Mustafa Ahmed

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ajayapc
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PostPosted: Fri Sep 30, 2011 4:11 am    Post subject: Floating Column Reply with quote

Dear SaahilPl don't even attempt to model or recommend floating columns in any buildings considering its vulnerability in eq/lateral loads. You may rethink appropriately and plan columns accordingly.

_Sincerely yours ... __________________________________
Ajay Chourasia




On Thu, 29/9/11, saahil <forum@sefindia.org> wrote:
Quote:

From: saahil <forum@sefindia.org>
Subject: [SEFI] Floating Column
To: general@sefindia.org
Date: Thursday, 29 September, 2011, 2:47 PM

           I am designing a G+13 building in etabs. The building has some of the
columns stubbed at 1st floor and the upper 12 floors are supported by
floating columns which are resting on beam at first floor lvl (please
see attached file). Two of the floating columns FC1 & FC2 having
different orientations are resting on the same beam.My problem is how
do I rest these floating columns (FC1 & FC2) on a single beam in etabs

Regards
Mustafa Ahmed
     



     
Download Attachments:
Floating_col-Model.pdf





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suresh_sharma
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Joined: 23 Mar 2011
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PostPosted: Fri Sep 30, 2011 1:07 pm    Post subject: Reply with quote

AJAY,what you have said about floating columns is theoretically correct but architects have been doing the audacity of providing floating columns.
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sakumar79
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Joined: 18 Apr 2008
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PostPosted: Sat Oct 01, 2011 1:49 am    Post subject: Reply with quote

Dear Sir,
   While I agree that architects use floating columns indiscriminately, one should take into account that the building is G+13 and not just G+1 or G+2. Under the circumstances, I feel floating columns should be strictly avoided. Even when you design only vertical load, if you try to design the first floor beam for the floating column load taking into account the high shear and moments, I think the beam depth would be greater than the stilt floor height.

   Hence I strongly suggest you get the architect to avoid the floating columns

Yours sincerely,
Arun
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vikram.jeet
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Joined: 26 Jan 2003
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PostPosted: Sat Oct 01, 2011 4:17 am    Post subject: Floating Column Reply with quote

Floating columns must be avoided as much as possible.

Transfer beam must be wide enough to accommodate both
the columns with different orientation of long dim

Transfer beam has be adequate and ,in case adjoining space is not
double height, the provision of orthogonal beams at floating column
locations connected to transfer girder will be structurally better.


May please refer earlier detailed postings by eminent  
members since this topic is discussed many times.

best regds

vikramjeet
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sakumar79
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Joined: 18 Apr 2008
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PostPosted: Sat Oct 01, 2011 11:02 am    Post subject: Reply with quote

Dear Sir,
   In continuation of Er. Vikramjeet's post, I would like to add one point. If your transfer girder is made wide to accomodate two floating columns, and if the columns are not aligned to the transfer girder, the point torsion in the transfer girder due to the eccentricity should be considered. This should be avoided since the torsion will be very large...

    Again, I reiterate that for a G+13 building, dont go for floating columns.

Arun
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rg.gupta
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Joined: 26 Jan 2003
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PostPosted: Sat Oct 01, 2011 2:33 pm    Post subject: Floating Column Reply with quote

dear sefians
jai hind
i also aggree with the views of all sefians who have expressed not to
go for such a option as it is very dangerous from the point of
stability and design as in this case
the vertical seismic will be alarmingly high, whereas in other normal
cases this is very negligible but here it is very defirent because of
modal masses are not considing with the supports and hanging on beams
from first floor above.
r g gupta

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lele_raj
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Joined: 26 Jan 2003
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PostPosted: Sun Oct 02, 2011 12:29 am    Post subject: Floating Column Reply with quote

One of the points which was made known to me for not going for floating column: Go for floating column only if you can provide a perfectly hinged joint, i.e. no transfer of moments, like a "ball" type joint. Any slight eccentricity will put huge BM (or torsion, depending on the direction) on the girder, yielding the floating column quite un-economical.

Best regards,

Rajendra (Raj) Lele





From: rg.gupta <forum@sefindia.org>
To: general@sefindia.org
Sent: Sunday, 2 October 2011 5:38 AM
Subject: [SEFI] Re: Floating Column

           dear sefians
jai hind
i also aggree with the views of all sefians who have expressed not to
go for such a option as it is very dangerous from the point of
stability and design as in this case
the vertical seismic will be alarmingly high, whereas in other normal
cases this is very negligible but here it is very defirent because of
modal masses are not considing with the supports and hanging on beams
from first floor above.
r g gupta

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suresh_sharma
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Joined: 23 Mar 2011
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PostPosted: Sun Oct 02, 2011 8:09 am    Post subject: Reply with quote

Dear Sri Gupta,

Why the vertical seismic will be vey high in case of floating columns?
Please elaborate.
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prof.arc
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Joined: 26 Jan 2003
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PostPosted: Sun Oct 02, 2011 11:13 pm    Post subject: Floating Column Reply with quote

the confusion is because of misnomer - floating COLUMN

It is not a column at all - it is just a vertical member but not transferring load directly to the foundation 

May be "Secondary Column" [like nomenclature of Secondary Beam] might be more appropriate.


A true Column on the other hand must start from the Foundation level.



Theoretically, nothing wrong with with such secondary column
But in practice, the joints are poorly analysed, designed and constructed


The most important part of a building are the columns in the lowest floor between foundation and first floor
and those columns are overstressed for horizontal loads - behaving like a stilt.


ARC


On Sun, Oct 2, 2011 at 12:03 PM, lele_raj <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
           One of the points which was made known to me for not going for floating column: Go for floating column only if you can provide a perfectly hinged joint, i.e. no transfer of moments, like a "ball" type joint. Any slight eccentricity will put huge BM (or torsion, depending on the direction) on the girder, yielding the floating column quite un-economical.




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