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deviationz SEFI Regulars
Joined: 07 Mar 2009 Posts: 32

Posted: Thu Jun 14, 2012 10:39 am Post subject: IS 456 Punching Shear 


List members,
According to IS 456, the punching shear capacity of concrete in ultimate loads is 0.25(fck)^{0.5}, where fck is the concrete cube strength
According to ACI 318, the punching shear capacity of concrete is = phi * 0.33 (f'c)^{0.5} = 0.2475(f'c) ^{0.5}, where f'c is the cylinder strength
If you use a relationship for fck = 1.25 fc', the Indian codes punching shear capacity is 0.2795 (f'c)^{0.5}
Something is amiss or it appears that the Indian code estimates the punching shear capacity of concrete to be 11% more than that of ACI.
Your thoughts please. 

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Dr. N. Subramanian General Sponsor
Joined: 21 Feb 2008 Posts: 5430 Location: Gaithersburg, MD, U.S.A.

Posted: Thu Jun 14, 2012 5:04 pm Post subject: Re: IS 456 Punching Shear 


Dear Er Deviationz(?!),
What do you mean by "list Members"?
First of all ACI code formula is empirical and can not be considered as accurate. It does not take into account size effect and reinforcement ratio. More comparisons may be found in my April 2005 ICJ paper "EVALUATION AND ENHANCING THE PUNCHING SHEAR RESISTANCE OF HIGHSTRENGTH CONCRETE SLABS". Better predictions can be made by using CEBFIP code formula or the Euro code formula. ACI and IS code formulae are similar.
Coming to your question, we can not simply compare ACI and IS code formula, as ACI code uses strength reduction factors 'phi' factors also and for punching it is 0.75. Hence if you apply that factor the strength to be used as per ACI for square column is 0.75 /3 sq.rt. (f'c) = 0.25 sq.rt. (f'c) = 0.224 sq.rt.(fck). Again as earlier said, it is only an app. eqn. based on Expt data of limited tests and does not include the factors mentioned earlier.
Best wishes
NS
deviationz wrote:  List members,
According to IS 456, the punching shear capacity of concrete in ultimate loads is 0.25(fck)^{0.5}, where fck is the concrete cube strength
According to ACI 318, the punching shear capacity of concrete is = phi * 0.33 (f'c)^{0.5} = 0.2475(f'c) ^{0.5}, where f'c is the cylinder strength
If you use a relationship for fck = 1.25 fc', the Indian codes punching shear capacity is 0.2795 (f'c)^{0.5}
Something is amiss or it appears that the Indian code estimates the punching shear capacity of concrete to be 11% more than that of ACI.
Your thoughts please. 


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es_jayakumar General Sponsor
Joined: 24 Nov 2011 Posts: 1379 Location: Cochin

Posted: Thu Feb 11, 2016 4:08 pm Post subject: 


Dear SEFIans,
Why does not Punching shear have any correlation with the reinforcement % of the RCC member ?
E S Jayakumar 

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Dr. N. Subramanian General Sponsor
Joined: 21 Feb 2008 Posts: 5430 Location: Gaithersburg, MD, U.S.A.

Posted: Thu Feb 11, 2016 9:43 pm Post subject: 


Dear Er Jayakumar,
It is a good question. As informed by me in an earlier email, The ACI code formula (and also the IS code formula, which is based on ACI formulabut the coefficient Betac is the inverse of that used in ACI) is empirical and can not be considered as accurate. It does not take into account size effect and reinforcement ratio.
According to ACI 31814 and IS 4562000, the strength is proportional to the square root of the specified concrete compressive strength; the other parameters affecting the punching strength are the ratio of shorter side to longer side of the supporting column, and the ratio of the dimension of supporting column to the effective depth of slab.
However, Eurocode 2, CEBFIP Model code and BS 8110 include additional parameters such as the flexural reinforcement ratio ρ or the thickness d of the slab (size effect). You may be aware that these codes consider cube root of f_{ck} instead of square root of f_{ck}, and also take the critical section at 1.5d to 2.0d from the face of the column.
Note that punching shear as well as shear reinforcement for resisting the same is still subjected to lot of research. Please read section 11.5.2 to 11.5.3 of my book on RC Design (OUP, 2014) for a summary of this research.
You may also be interested to read the paper by Dr. Ruiz & Prof. Muttoni:http://infoscience.epfl.ch/record/163107/files/Fernandez10b
Since punching shear is a sudden failure, and the flexural reinforcement ratio in slabs is not considerable as compared to beams, the consideration of flexural reinforcement ratio may not yield much difference in the punching shear strength of slabs.
It is always better to provide at least two rods going through the column width in flat slabs, to avoid progressive collapse.
Warm regards,
Subramanian
es_jayakumar wrote:  Dear SEFIans,
Why does not Punching shear have any correlation with the reinforcement % of the RCC member ?
E S Jayakumar 


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es_jayakumar General Sponsor
Joined: 24 Nov 2011 Posts: 1379 Location: Cochin

Posted: Fri Feb 12, 2016 12:36 am Post subject: 


Dear NS Sir,
Thanks for your prompt reply. You mention that punching shear failure is a sudden failure. But, the flat RCC member (footing, raft or flat slab) that is prone to punching shear failure would have reinforcement bars in both directions in it, which can obviously offer some degree of resistance against the punching shear failure, as in the case of oneway shear. If we devise some formula that accounts for the punching shear resistance contributed by steel also, we can save on quantity of RCC for such members, specifically for slab type raft foundation and flat slab, the depth of which is governed by the punching shear criterion.
Regards,
E S Jayakumar 

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Dr. N. Subramanian General Sponsor
Joined: 21 Feb 2008 Posts: 5430 Location: Gaithersburg, MD, U.S.A.

Posted: Fri Feb 12, 2016 1:45 am Post subject: 


Dear Er Jayakumar
You may use Eurocode formula, which includes reinforcement, and check whether there will be considerable savings. I think it will not be considerable.
Regards
NS
es_jayakumar wrote:  Dear NS Sir,
Thanks for your prompt reply. You mention that punching shear failure is a sudden failure. But, the flat RCC member (footing, raft or flat slab) that is prone to punching shear failure would have reinforcement bars in both directions in it, which can obviously offer some degree of resistance against the punching shear failure, as in the case of oneway shear. If we devise some formula that accounts for the punching shear resistance contributed by steel also, we can save on quantity of RCC for such members, specifically for slab type raft foundation and flat slab, the depth of which is governed by the punching shear criterion.
Regards,
E S Jayakumar 


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jdbuch SEFI Member
Joined: 24 May 2008 Posts: 16

Posted: Fri Feb 12, 2016 6:00 am Post subject: IS 456 Punching Shear 


Dear Prof Ragon,
I have not received the attachments mentioned in your mail. I shall be grateful if you send these.
Regards
J.D.Buch
From: "Rangan" <forum@sefindia.org>
Sent: Fri, 12 Feb 2016 08:27:33
To: general@sefindia.org
Subject: [SEFI] IS 456 Punching Shear
Dear Dr Subramanian and Er Jayakumar,
You may be interested in the attachments. describing the shear design in slabs from the Australian Standard for Concrete Structures. The first three attachments describe the shear design provisions for slabs given in the Australian Standard for Concrete Structures, and the last attachment is a background paper. These shear provisions are is use in Australia from 1987, based on extensive experimental and analytical research carried out then.
Best regards
Vijaya Rangan
Professor B. Vijaya Rangan, BE PhD FIE Aust FACI Hon FICI Hon Mem Conc Inst Aust
Emeritus Professor of Civil Engineering
Curtin University
Perth, Australia
Email: V.Rangan@curtin.edu.au (V.Rangan@curtin.edu.au)
From: Dr. N. Subramanian <forum@sefindia.org>
Sent: Friday, 12 February 2016 5:43 AM
To: general@sefindia.org
Subject: [SEFI] Re: IS 456 Punching Shear
Dear Er Jayakumar,
It is a good question. As informed by me in an earlier email, The ACI code formula (and also the IS code formula, which is based on ACI formulabut the coefficient Betac is the inverse of that used in ACI) is empirical and can not be considered as accurate. It does not take into account size effect and reinforcement ratio.
According to ACI 31814 and IS 4562000, the strength is proportional to the square root of the specified concrete compressive strength; the other parameters affecting the punching strength are the ratio of shorter side to longer side of the supporting column, and the ratio of the dimension of supporting column to the effective depth of slab.
However, Eurocode 2, CEBFIP Model code and BS 8110 include additional parameters such as the flexural reinforcement ratio ρ or the thickness d of the slab (size effect). You may be aware that these codes consider cube root of f_{ck} instead of square root of f_{ck}, and also take the critical section at 1.5d to 2.0d from the face of the column.
Note that punching shear as well as shear reinforcement for resisting the same is still subjected to lot of research. Please read section 11.5.2 to 11.5.3 of my book on RC Design (OUP, 2014) for a summary of this research.
You may also be interested to read the paper by Dr. Ruiz & Prof. Muttoni:http://infoscience.epfl.ch/record/163107/files/Fernandez10b
Since punching shear is a sudden failure, and the flexural reinforcement ratio in slabs is not considerable as compared to beams, the consideration of flexural reinforcement ratio may not yield much difference the punching shear strength of slabs.
It is always better to provide at least two rods going through the column width in flat slabs, to avoid progressive collapse.
Warm regards,
Subramanian
es_jayakumar wrote: Dear SEFIans,
Why does not Punching shear have any correlation with the reinforcement % of the RCC member ?
E S Jayakumar
Download Attachments:
Seng20441410092109570.pdf
Seng20441410092109571.pdf
Seng20441410092109572.pdf
Prof_Rangan_Shear_Cem&Conc_Composites.pdf
Get your own FREE website, FREE domain & FREE mobile app with Company email.
Know More > >
Posted via Email 

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roopasunilkv SEFI Member
Joined: 02 Jul 2009 Posts: 4

Posted: Fri Feb 12, 2016 9:00 am Post subject: IS 456 Punching Shear 


Punching Shear Strength of Reinforced Concrete Slabs without Transverse Reinforcementhow it is possible for flat slab???????
On 12 February 2016 at 08:26, Rangan <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:  Dear Dr Subramanian and Er Jayakumar,
You may be interested in the attachments. describing the shear design in slabs from the Australian Standard for Concrete Structures. The first three attachments describe the shear design provisions for slabs given in the Australian Standard for Concrete Structures, and the last attachment is a background paper. These shear provisions are is use in Australia from 1987, based on extensive experimental and analytical research carried out then.
Best regards
Vijaya Rangan
Professor B. Vijaya Rangan, BE PhD FIE Aust FACI Hon FICI Hon Mem Conc Inst Aust
Emeritus Professor of Civil Engineering
Curtin University
Perth, Australia
Email: V.Rangan@curtin.edu.au (V.Rangan@curtin.edu.au) (V.Rangan@curtin.edu.au (V.Rangan@curtin.edu.au))
From: Dr. N. Subramanian
Sent: Friday, 12 February 2016 5:43 AM
To: general@sefindia.org (general@sefindia.org)
Subject: [SEFI] Re: IS 456 Punching Shear
Dear Er Jayakumar,
It is a good question. As informed by me in an earlier email, The ACI code formula (and also the IS code formula, which is based on ACI formulabut the coefficient Betac is the inverse of that used in ACI) is empirical and can not be considered as accurate. It does not take into account size effect and reinforcement ratio.
According to ACI 31814 and IS 4562000, the strength is proportional to the square root of the specified concrete compressive strength; the other parameters affecting the punching strength are the ratio of shorter side to longer side of the supporting column, and the ratio of the dimension of supporting column to the effective depth of slab.
However, Eurocode 2, CEBFIP Model code and BS 8110 include additional parameters such as the flexural reinforcement ratio ρ or the thickness d of the slab (size effect). You may be aware that these codes consider cube root of f_{ck} instead of square root of f_{ck}, and also take the critical section at 1.5d to 2.0d from the face of the column.
Note that punching shear as well as shear reinforcement for resisting the same is still subjected to lot of research. Please read section 11.5.2 to 11.5.3 of my book on RC Design (OUP, 2014) for a summary of this research.
You may also be interested to read the paper by Dr. Ruiz & Prof. Muttoni:http://infoscience.epfl.ch/record/163107/files/Fernandez10b
Since punching shear is a sudden failure, and the flexural reinforcement ratio in slabs is not considerable as compared to beams, the consideration of flexural reinforcement ratio may not yield much difference the punching shear strength of slabs.
It is always better to provide at least two rods going through the column width in flat slabs, to avoid progressive collapse.
Warm regards,
Subramanian
es_jayakumar wrote: Dear SEFIans,
Why does not Punching shear have any correlation with the reinforcement % of the RCC member ?
E S Jayakumar
Download Attachments:
Seng20441410092109570.pdf
Seng20441410092109571.pdf
Seng20441410092109572.pdf
Prof_Rangan_Shear_Cem&Conc_Composites.pdf

Posted via Email 

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jdbuch SEFI Member
Joined: 24 May 2008 Posts: 16

Posted: Sat Feb 13, 2016 3:00 am Post subject: IS 456 Punching Shear 


Thanks.
Regards.
J.D.Buch
From: Vijaya Rangan <V.Rangan@curtin.edu.au>
Sent: Fri, 12 Feb 2016 10:50:12
To: Jitendra Dolarrai Buch <jdbuch@rediffmail.com>, "general@sefindia.org" <general@sefindia.org>
Subject: Re: [SEFI] IS 456 Punching Shear
From: jdbuch@rediffmail.com <jdbuch@rediffmail.com> on behalf of Jitendra Dolarrai Buch <jdbuch@rediffmail.com>
Sent: Friday, 12 February 2016 1:10 PM
To: general@sefindia.org; Vijaya Rangan
Subject: Re: [SEFI] IS 456 Punching Shear
Dear Prof Ragon,
I have not received the attachments mentioned in your mail. I shall be grateful if you send these.
Regards
J.D.Buch
From: "Rangan" <forum@sefindia.org>
Sent: Fri, 12 Feb 2016 08:27:33
To: general@sefindia.org
Subject: [SEFI] IS 456 Punching Shear
Dear Dr Subramanian and Er Jayakumar,
You may be interested in the attachments. describing the shear design in slabs from the Australian Standard for Concrete Structures. The first three attachments describe the shear design provisions for slabs given in the Australian Standard for Concrete Structures, and the last attachment is a background paper. These shear provisions are is use in Australia from 1987, based on extensive experimental and analytical research carried out then.
Best regards
Vijaya Rangan
Professor B. Vijaya Rangan, BE PhD FIE Aust FACI Hon FICI Hon Mem Conc Inst Aust
Emeritus Professor of Civil Engineering
Curtin University
Perth, Australia
Email: V.Rangan@curtin.edu.au (V.Rangan@curtin.edu.au)
From: Dr. N. Subramanian <forum@sefindia.org>
Sent: Friday, 12 February 2016 5:43 AM
To: general@sefindia.org
Subject: [SEFI] Re: IS 456 Punching Shear
Dear Er Jayakumar,
It is a good question. As informed by me in an earlier email, The ACI code formula (and also the IS code formula, which is based on ACI formulabut the coefficient Betac is the inverse of that used in ACI) is empirical and can not be considered as accurate. It does not take into account size effect and reinforcement ratio.
According to ACI 31814 and IS 4562000, the strength is proportional to the square root of the specified concrete compressive strength; the other parameters affecting the punching strength are the ratio of shorter side to longer side of the supporting column, and the ratio of the dimension of supporting column to the effective depth of slab.
However, Eurocode 2, CEBFIP Model code and BS 8110 include additional parameters such as the flexural reinforcement ratio ρ or the thickness d of the slab (size effect). You may be aware that these codes consider cube root of f_{ck} instead of square root of f_{ck}, and also take the critical section at 1.5d to 2.0d from the face of the column.
Note that punching shear as well as shear reinforcement for resisting the same is still subjected to lot of research. Please read section 11.5.2 to 11.5.3 of my book on RC Design (OUP, 2014) for a summary of this research.
You may also be interested to read the paper by Dr. Ruiz & Prof. Muttoni:http://infoscience.epfl.ch/record/163107/files/Fernandez10b
Since punching shear is a sudden failure, and the flexural reinforcement ratio in slabs is not considerable as compared to beams, the consideration of flexural reinforcement ratio may not yield much difference the punching shear strength of slabs.
It is always better to provide at least two rods going through the column width in flat slabs, to avoid progressive collapse.
Warm regards,
Subramanian
es_jayakumar wrote: Dear SEFIans,
Why does not Punching shear have any correlation with the reinforcement % of the RCC member ?
E S Jayakumar
Download Attachments:
Seng20441410092109570.pdf
Seng20441410092109571.pdf
Seng20441410092109572.pdf
Prof_Rangan_Shear_Cem&Conc_Composites.pdf
Get your own FREE website, FREE domain & FREE mobile app with Company email.
Know More >
Get your own FREE website, FREE domain & FREE mobile app with Company email.
Know More > >
Posted via Email 

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es_jayakumar General Sponsor
Joined: 24 Nov 2011 Posts: 1379 Location: Cochin

Posted: Mon Feb 15, 2016 12:46 am Post subject: 


Dear NS Sir,
Can you please intimate the Eurocode formula for punching shear, that takes into account the flexural reinforcement percentage too ?
Regards,
E S Jayakumar 

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