www.sefindia.org

[deviationz]

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.

[Dr. N. Subramanian]

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 HIGH-STRENGTH CONCRETE SLABS". Better predictions can be made by using CEB-FIP  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

[es_jayakumar]

Dear SEFIans,

Why does not Punching shear have any correlation with the reinforcement % of the RCC member ?

E S Jayakumar

[Dr. N. Subramanian]

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 formula-but 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 318-14 and IS 456-2000,  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, CEB-FIP 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]

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 one-way 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

[Dr. N. Subramanian]

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

[jdbuch]

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 formula-but 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 318-14 and IS 456-2000, 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, CEB-FIP 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:
Seng204-41410092109570.pdf
Seng204-41410092109571.pdf
Seng204-41410092109572.pdf
Prof_Rangan_Shear_Cem&Conc_Composites.pdf



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Posted via Email

[roopasunilkv]

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:

[jdbuch]

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 formula-but 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 318-14 and IS 456-2000, 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, CEB-FIP 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:
Seng204-41410092109570.pdf
Seng204-41410092109571.pdf
Seng204-41410092109572.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

[es_jayakumar]

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