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Floating Column
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chidub
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PostPosted: Thu Aug 09, 2018 5:30 pm    Post subject: Floating Column Reply with quote

Thank you

On Thu 9 Aug, 2018, 10:23 PM sangeeta_wij, <forum@sefindia.org (forum@sefindia.org)> wrote:

Quote:
           First of all, a floating column is really not a column and secondly, never ever use it in a seismic zone III IV or V structure as even the gravity columns have to be checked for deflection compatibility as   Stated in the relevant clause of 1893. However, my sincere suggestion is to delete the terms like hidden beams and floating columns from your vocabulary as far as seismic design is concerned.

Regards
Sangeeta Wij
On Thu, 9 Aug 2018 at 9:14 PM, sharathkcu forum@sefindia.org (forum@sefindia.org))> wrote:

Quote:
           Dear Kumaresan,

According to IS 1893:2016 part 1 table 6, if floating column is part of primary lateral load resisting system, it is prohibited to use. Otherwise if it's only to resist gravity loads, you can design it as a conventional column using IS 456:2000.


On Thu, Aug 9, 2018, 12:51 PM r.kumaresancivil@gmail.co (r.kumaresancivil@gmail.co) (r.kumaresancivil@gmail.co (r.kumaresancivil@gmail.co)) (r.kumaresancivil@gmail.co (r.kumaresancivil@gmail.co) (r.kumaresancivil@gmail.co (r.kumaresancivil@gmail.co))) forum@sefindia.org (forum@sefindia.org) (forum@sefindia.org (forum@sefindia.org)))> wrote:

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mohd_arastu
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PostPosted: Thu Aug 09, 2018 5:30 pm    Post subject: Floating Column Reply with quote

Dear Kumaresan


Read the clause 5.5 of IS 13920:2016


Buildings with floating columns and set back columns perform poorly, when any such irregularities are adopted, detailed nonlinear analyses shall be performed to demonstrate that there is no threat to lss of life and property.

On Thu, Aug 9, 2018, 9:13 PM sharathkcu <forum@sefindia.org (forum@sefindia.org)> wrote:

[quote]            Dear Kumaresan,

According to IS 1893:2016 part 1 table 6, if floating column is part of primary lateral load resisting system, it is prohibited to use. Otherwise if it's only to resist gravity loads, you can design it as a conventional column using IS 456:2000.


On Thu, Aug 9, 2018, 12:51 PM r.kumaresancivil@gmail.co (r.kumaresancivil@gmail.co) (r.kumaresancivil@gmail.co (r.kumaresancivil@gmail.co)) forum@sefindia.org (forum@sefindia.org))> wrote:

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vgrelan
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PostPosted: Thu Aug 09, 2018 7:30 pm    Post subject: Floating Column Reply with quote

Hi,Why to discourage someone from designing some adventurous designs? You may suggest that even if you design a floating column, the deflection check may make the structure uneconomical. 


On Thu 9 Aug, 2018, 10:22 PM sangeeta_wij, <forum@sefindia.org (forum@sefindia.org)> wrote:

Quote:
           First of all, a floating column is really not a column and secondly, never ever use it in a seismic zone III IV or V structure as even the gravity columns have to be checked for deflection compatibility as   Stated in the relevant clause of 1893. However, my sincere suggestion is to delete the terms like hidden beams and floating columns from your vocabulary as far as seismic design is concerned.

Regards
Sangeeta Wij
On Thu, 9 Aug 2018 at 9:14 PM, sharathkcu forum@sefindia.org (forum@sefindia.org))> wrote:

Quote:
           Dear Kumaresan,

According to IS 1893:2016 part 1 table 6, if floating column is part of primary lateral load resisting system, it is prohibited to use. Otherwise if it's only to resist gravity loads, you can design it as a conventional column using IS 456:2000.


On Thu, Aug 9, 2018, 12:51 PM r.kumaresancivil@gmail.co (r.kumaresancivil@gmail.co) (r.kumaresancivil@gmail.co (r.kumaresancivil@gmail.co)) (r.kumaresancivil@gmail.co (r.kumaresancivil@gmail.co) (r.kumaresancivil@gmail.co (r.kumaresancivil@gmail.co))) forum@sefindia.org (forum@sefindia.org) (forum@sefindia.org (forum@sefindia.org)))> wrote:

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sudhindra
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PostPosted: Thu Aug 09, 2018 7:30 pm    Post subject: Floating Column Reply with quote

Dear Kumeran,

The new seismic code says the contribution of lateral force due to seismic force in floating column should not be considered but it insist to introduce outer core RCC wall and also it should be designed for greater than 90 percentage of seismic force of total force.I hope you will understand my reply.
Sent from Yahoo Mail on Android

[quote]  On Thu, 9 Aug 2018 at 21:12, sharathkcu
<forum@sefindia.org> wrote:

           Dear Kumaresan,

According to IS 1893:2016 part 1 table 6, if floating column is part of primary lateral load resisting system, it is prohibited to use. Otherwise if it's only to resist gravity loads, you can design it as a conventional column using IS 456:2000.


On Thu, Aug 9, 2018, 12:51 PM r.kumaresancivil@gmail.co (r.kumaresancivil@gmail.co) (r.kumaresancivil@gmail.co (r.kumaresancivil@gmail.co)) forum@sefindia.org)> wrote:

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Dr. N. Subramanian
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PostPosted: Thu Aug 09, 2018 8:38 pm    Post subject: Re: Floating Column Reply with quote

I wish to appreciate Er. Sangeeta Wij for giving the correct advice.

Columns should spring from the foundation concrete, which is well spread and transfers all the loads and moments to the earth below, through the well designed and detailed foundation system. But the so called "floating columns"(which were basically invented by the architects in order to fulfill their crazy ideas, without considering the structural implications) are springing from narrow, may be deep beams. When there is an earthquake or lateral load, enormous amounts of moments and shear are transferred at the joint of this floating column and supporting beam, which has to be resisted by the beam supporting it. The moments will cause heavy torsion on the beam. Hence in several past earthquakes the frames with floating columns have failed. The torsion may be reduced by cross-beam provided at this point of the same depth, but will complicate the joint reinforcement detailing.

The practice of floating columns in the upper storeys is very common in the cities in India. Close-up view shows shear cracks in the cantilever stub beam supporting a floating column in a 4-storey RC frame residential building in Ahmedabad                               (Source: http://www.iitk.ac.in/nicee/EQ_Reports/Bhuj/build_rc1.htm).

In the previous versions of IS 1893(Part 1) there was no mention of floating columns. To be honest, I heard of these terms, floating column and hidden beams only when I practiced with architects. But the committee of the present version (2016) of the code realized the danger of floating columns and hence mentioned it specifically in pp.16,Table 6, item (vi), and prohibits its use. The code considers it as a vertical irregularity. It has to be noted that the load path is disturbed when we have floating columns.

Of course in non-seismic zones, the floating column may not pose much danger, but the joint has to be properly designed and detailed.

The beams have flexural strength only when they have adequate depth. Hence the so called " hidden beams" or "concealed beams", which have a depth equal to the slab depth, which may in practical cases will vary from 100 mm to 150 mm, will not have enough flexural strength. Hence they  may be used only when the span is very small, say 6 to 6.5 feet. See also Section 5.11 of my RC Design book, OUP, 2013.

Best wishes
Subramanian

[quote="sangeeta_wij"]First of all, a floating column is really not a column and secondly, never ever use it in a seismic zone III IV or V structure as even the gravity columns have to be checked for deflection compatibility as   Stated in the relevant clause of 1893. However, my sincere suggestion is to delete the terms like hidden beams and floating columns from your vocabulary as far as seismic design is concerned.

Regards
Sangeeta Wij
On Thu, 9 Aug 2018 at 9:14 PM, sharathkcu <forum> wrote:

Quote:
            Dear Kumaresan,

According to IS 1893:2016 part 1 table 6, if floating column is part of primary lateral load resisting system, it is prohibited to use. Otherwise if it's only to resist gravity loads, you can design it as a conventional column using IS 456:2000.


On Thu, Aug 9, 2018, 12:51 PM r.kumaresancivil@gmail.co (r.kumaresancivil@gmail.co) (r.kumaresancivil@gmail.co (r.kumaresancivil@gmail.co)) forum@sefindia.org (forum@sefindia.org))> wrote:

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Dr. N. Subramanian
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PostPosted: Fri Aug 10, 2018 12:27 am    Post subject: Re: Floating Column Reply with quote

[quote="Dr. N. Subramanian"]I wish to appreciate Er. Sangeeta Wij for giving the correct advice.

Columns should spring from the foundation concrete, which is well spread and transfers all the loads and moments to the earth below, through the well designed and detailed foundation system. But the so called "floating columns"(which were basically invented by the architects in order to fulfill their crazy ideas, without considering the structural implications) are springing from narrow, may be deep beams. When there is an earthquake or lateral load, enormous amounts of moments and shear are transferred at the joint of this floating column and supporting beam, which has to be resisted by the beam supporting it. The moments will cause heavy torsion on the beam. Hence in several past earthquakes the frames with floating columns have failed. The torsion may be reduced by cross-beam provided at this point of the same depth, but will complicate the joint reinforcement detailing.In addition, note that EQ loads change directions and due to this the shear strength of joint concrete may be lost, leading to failure.

The practice of floating columns in the upper storeys is very common in the cities in India. Close-up view shows shear cracks in the cantilever stub beam supporting a floating column in a 4-storey RC frame residential building in Ahmedabad                               (Source: http://www.iitk.ac.in/nicee/EQ_Reports/Bhuj/build_rc1.htm).

In the previous versions of IS 1893(Part 1) there was no mention of floating columns. To be honest, I heard of these terms, floating column and hidden beams only when I practiced with architects. But the committee of the present version (2016) of the code realized the danger of floating columns and hence mentioned it specifically in pp.16,Table 6, item (vi), and prohibits its use. The code considers it as a vertical irregularity. It has to be noted that the load path is disturbed when we have floating columns.

Of course in non-seismic zones, the floating column may not pose much danger, but the joint has to be properly designed and detailed.

The beams have flexural strength only when they have adequate depth. Hence the so called " hidden beams" or "concealed beams", which have a depth equal to the slab depth, which may in practical cases will vary from 100 mm to 150 mm, will not have enough flexural strength. Hence they  may be used only when the span is very small, say 6 to 6.5 feet. See also Section 5.11 of my RC Design book, OUP, 2013.

Best wishes
Subramanian

sangeeta_wij wrote:
First of all, a floating column is really not a column and secondly, never ever use it in a seismic zone III IV or V structure as even the gravity columns have to be checked for deflection compatibility as   Stated in the relevant clause of 1893. However, my sincere suggestion is to delete the terms like hidden beams and floating columns from your vocabulary as far as seismic design is concerned.

Regards
Sangeeta Wij
On Thu, 9 Aug 2018 at 9:14 PM, sharathkcu <forum> wrote:

Quote:
            Dear Kumaresan,

According to IS 1893:2016 part 1 table 6, if floating column is part of primary lateral load resisting system, it is prohibited to use. Otherwise if it's only to resist gravity loads, you can design it as a conventional column using IS 456:2000.


On Thu, Aug 9, 2018, 12:51 PM r.kumaresancivil@gmail.co (r.kumaresancivil@gmail.co) (r.kumaresancivil@gmail.co (r.kumaresancivil@gmail.co)) forum@sefindia.org (forum@sefindia.org))> wrote:

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SATYAPAUL
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PostPosted: Fri Aug 10, 2018 3:30 am    Post subject: Floating Column Reply with quote

I AM NOT REFERRING TO ANY CODE OF PRACTICE.PROVIDE HINGE EITHER AT TOP OR BOTTOM TO JUST TRANSFER  GRAVITY LOAD ONLY.OTHERS CAN ALSO THINK ABOUT THIS. SATYA PAL On Thu, 09 Aug 2018 22:21:10 +0530 "sangeeta_wij"  wrote >                   First of all, a floating column is really not a column and secondly, never ever use it in a  seismic zone III IV or V structure as even the gravity columns have to be checked for deflection  compatibility as   Stated in the relevant clause of 1893. However, my sincere suggestion is to delete  the terms like hidden beams and floating columns from your vocabulary as far as seismic design is  concerned. >  > Regards > Sangeeta Wij > On Thu, 9 Aug 2018 at 9:14 PM, sharathkcu wrote: >  > [quote]            Dear Kumaresan, >  > According to IS 1893:2016 part 1 table 6, if floating column is part of primary lateral load resisting  system, it is prohibited to use. Otherwise if it's only to resist gravity loads, you can design it as a  conventional column using IS 456:2000. >  >  > On Thu, Aug 9, 2018, 12:51 PM r.kumaresancivil@gmail.co (r.kumaresancivil@gmail.co)  (r.kumaresancivil@gmail.co (r.kumaresancivil@gmail.co)) forum@sefindia.org (forum@sefindia.org))>  wrote: >  >       --auto removed-- >       > >  >  > --

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