www.www.bussiapp.com

[amarjeetsingh]

dear all,

for design of shear stirrups the is:456-2000 in clause 40.4 page 73 mentions that the characterstic strength of the stirrups or bent up reinforcement shall not be greater than 415 N/sqmm . if we use Fe 500 then also do we have to take Fy as 415???. if yes then what is the reason behind it??

regrds

amarjeet singh

Posted via Email

[Dr. N. Subramanian]

Dear Mr. Amarjeet,

It is a good question.

Yes. For design purposes you have to take fy as 415 N/sqmm only even if you use higher grade steel. SP 24:1983 says the following reasons:
1) in order to limit the crack width, as crack width and grade of steel are inter-related .
2)高档强化期间可能受损bending, as it is tough to bend high grade rebars.

Similar clause exists in ACI 318-08 also. I am giving below the commentary given in ACI
"Limiting the values of fy and fyt used in design of shear reinforcement to 420 MPa provides a control on diagonal crack width.Research has indicated that the performance of higher strength steels as shear reinforcement has been satisfactory. In particular, full-scale beam tests described in Reference 11.21 indicated that the widths of inclined shear cracks at service load levels were less for beams reinforced with smaller diameter welded deformed wire reinforcement cages designed on the basis of a yield strength of 520 MPa than beams reinforced with deformed Grade 420 stirrups.
11.21.Griezic, a;做饭,w . d;米切尔,D。�Tests to Determine Performance of Deformed Welded-Wire Fabric Stirrups,� ACI Structural Journal, V. 91, No. 2, Mar.-Apr. 1994, pp. 211-220."

Interestingly the NZ code(NZS 3101) limits fy to 500 MPa.

Shear strength of concrete beams is the most researched area in RC. The current Indian code provisions are old and I have compared them with the other codes in the following paper:
Subramanian N., Shear strength of high strength concrete beams: Review of Codal Provisions, The Indian Concrete Journal, V.77, No.5, May 2003, pp.1090-1094.

The ACI as well as Indian (based on ACI Code) code provisions do not include longitudinal reinforcement ratio and size effect. As a result of the research done by Prof. Collins and his associates, The Canadian code has adopted a formulation based on the modified compression theory, which is more accurate(though involved in calculation) and incorporates influences of size effect and longitudinal reinforcement. Hope the next version of the Indian Code adopts such an accurate model, as some failures have occured according to Prof. Collins, due to the shortcoming of ACI code( See Lubell,A.S., E. C. Bentz, and M. P. Collins, Safe Shear Design of Large, wide Beams, Concrete International, Jan. 2004)

Some of you in SEFI may also be interested in looking at the recent paper published in ASCE Structural Journal, Jan 09 issue:
Lubell,A.S., E. C. Bentz, and M. P. Collins,Influence of Longitudinal Reinforcement on One-Way Shear in Slabs and Wide Beams

Best wishes
NS

Dr.N.Subramanian,Ph.D.,F.ASCE, M.ACI,

Consulting Structural Engineer
Maryland, USA

See my books at:www.multi-science.co.uk/subramanian-book.htm
www.oup.co.in/search_detail.php?id=144559





--- OnThu, 1/8/09, amarjeet singhwrote:

[Dr. N. Subramanian]

Hi,

In my reply to this question, I wrote that
"The ACI as well as Indian (based on ACI Code) code provisions do not include longitudinal reinforcement ratio and size effect."
Which is not correct. The IS code provisions on shear strength of concrete is based on Research conducted by Prof. B.V. Rangan of Australia, and takes into account flexural reinforcement but not size effect.

NS

[pkmaini]

Yes, It is due to copying phenomenon of BIS. They should know that by limiting YS does not mean prohibiting the use of Fe500. Even Fe 600 bars has bend radius of 2T . Fe 500 can be bent in 1T . there are no cracks in steel during bending upto 2T.

now , on aspect of crackwidth which is said to inversely proportional to YSt is also not logical . crack width can only depend on spacing of reinforcement bars. The ideal case would have to use lower dia bars of higher yst at close spacing .

_puneet


On 1/8/09,amarjeet singhforum@www.bussiapp.com)> wrote:

[amarjeetsingh]

sir,

then no point using higher grade steel in the foundations where normally shear is the governing criterion for providing reinforceemnt.

also what is the corelation between the crackwidth and the grade of steel. can we say that what percentage increase in crack width will be there if we use Fe500 instead steel instaed of Fe415 for the same reinforcement dia and the spacing.


thanks in advance

regrds

amarjeet singh


On Fri, Jan 9, 2009 at 9:51 AM, pkmaini forum@www.bussiapp.com)> wrote:
[quote] Yes, It is due to copying phenomenon of BIS. They should know that by limiting YS does not mean prohibiting the use of Fe500. Even Fe 600 bars has bend radius of 2T . Fe 500 can be bent in 1T . there are no cracks in steel during bending upto 2T.

now , on aspect of crackwidth which is said to inversely proportional to YSt is also not logical . crack width can only depend on spacing of reinforcement bars. The ideal case would have to use lower dia bars of higher yst at close spacing .

_puneet


On 1/8/09, amarjeet singhforum@www.bussiapp.com(forum@www.bussiapp.com))> wrote:--auto removed--

Posted via Email

[bsec]

Dear Dr Subramanian,

Thanks very much indeed for such an elaborate explanation on the subject matter.

Interestingly, the Eurocodes (EC2) do not put any restriction on the grade of steel for calculation of shear reinforcement.

As far as IS:456 is concerned, I think this clause was put in line with the British Code (BS:8110). Fe 500 was not in much use at the time of writing of the code. I think in the coming revisions, this restriction on steel strength for shear may go, in line with Euro code.

As mentioned by Prof. L A Clarke, shear phenomenon in concrete is the most researched subject in civil engineering and still, the least understood amongst all the phenomenon. That is the reason for frequent changes in the design philosophy in shear, world over.

With best wishes

Alok Bhowmick




-----Original Message-----
From:drnsmani [mailto:forum@www.bussiapp.com]
Sent:Thursday, January 08, 2009 11:02 PM
To:general@www.bussiapp.com
Subject:[SEFI] Re: use of fe500 steel in stirupps

Dear Mr. Amarjeet,

It is a good question.

Yes. For design purposes you have to take fy as 415 N/sqmm only even if you use higher grade steel. SP 24:1983 says the following reasons:
1) in order to limit the crack width, as crack width and grade of steel are inter-related .
2)高档强化期间可能受损bending, as it is tough to bend high grade rebars.

Similar clause exists in ACI 318-08 also. I am giving below the commentary given in ACI
"Limiting the values of fy and fyt used in design of shear reinforcement to 420 MPa provides a control on diagonal crack width.Research has indicated that the performance of higher strength steels as shear reinforcement has been satisfactory. In particular, full-scale beam tests described in Reference 11.21 indicated that the widths of inclined shear cracks at service load levels were less for beams reinforced with smaller diameter welded deformed wire reinforcement cages designed on the basis of a yield strength of 520 MPa than beams reinforced with deformed Grade 420 stirrups.
11.21.Griezic, a;做饭,w . d;米切尔,D。“Tests to Determine Performance of Deformed Welded-Wire Fabric Stirrups,” ACI Structural Journal, V. 91, No. 2, Mar.-Apr. 1994, pp. 211-220."

Interestingly the NZ code(NZS 3101) limits fy to 500 MPa.

Shear strength of concrete beams is the most researched area in RC. The current Indian code provisions are old and I have compared them with the other codes in the following paper:
假假假MicrosoftInternetExplor正常0er4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} Subramanian N., Shear strength of high strength concrete beams: Review of Codal Provisions, The Indian Concrete Journal, V.77, No.5, May 2003, pp.1090-1094.

The ACI as well as Indian (based on ACI Code) code provisions do not include longitudinal reinforcement ratio and size effect. As a result of the research done by Prof. Collins and his associates, The Canadian code has adopted a formulation based on the modified compression theory, which is more accurate(though involved in calculation) and incorporates influences of size effect and longitudinal reinforcement. Hope the next version of the Indian Code adopts such an accurate model, as some failures have occured according to Prof. Collins, due to the shortcoming of ACI code( See Lubell,A.S., E. C. Bentz, and M. P. Collins, Safe Shear Design of Large, wide Beams, Concrete International, Jan. 2004)

Some of you in SEFI may also be interested in looking at the recent paper published in ASCE Structural Journal, Jan 09 issue:
Lubell,A.S., E. C. Bentz, and M. P. Collins,Influence of Longitudinal Reinforcement on One-Way Shear in Slabs and Wide Beams

Best wishes
NS

Dr.N.Subramanian,Ph.D.,F.ASCE, M.ACI,

Consulting Structural Engineer
Maryland, USA

See my books at:www.multi-science.co.uk/subramanian-book.htm
www.oup.co.in/search_detail.php?id=144559





--- OnThu, 1/8/09, amarjeet singhwrote:
--auto removed--

Posted via Email

[ibarua]

10th Jan 2009

My experience is that the design of stirrups (their spacing) is finally determined by the provisions of the Codes given in IS:456 & IS:13923. These are to ensure ductility.

Indrajit Barua.

On Thu, 08 Jan 2009 drnsmani wrote :

[mitalsanghvi]

Nowadays the leading steel provider company tata is supplying Fe 500 only with improved ductility. called super ductile steel...
in our region they have stopped supplying Fe 415..


On 1/10/09,ibaruaforum@www.bussiapp.com)> wrote: [quote] 10th Jan 2009

My experience is that the design of stirrups (their spacing) is finally determined by the provisions of the Codes given in IS:456 & IS:13923. These are to ensure ductility.

Indrajit Barua.

On Thu, 08 Jan 2009 drnsmani wrote :
--auto removed--

Posted via Email

[Dr. N. Subramanian]

Dear Mitalsanghvi,

You have to write to BIS about it and ask them for the remedy, because the next edition of IS 456 may be published perhaps after 10 years. They may atleast release an amendment.

I take this opportunity to bring to the notice that even 33 grade cement is not available and grade 43 and 53 only are available. For ordinary buildings with M20 concrete, I feel that 33 Grade cement only has to be used, as the heat of hydration will be less and considering the poor curing in most of the Indian construction sites(except when handled by reputed construction companies).

Best wishes
NS


Dr.N.Subramanian,Ph.D.,F.ASCE, M.ACI,

Consulting Structural Engineer
Maryland, USA

See my books at:www.multi-science.co.uk/subramanian-book.htm
www.oup.co.in/search_detail.php?id=144559





--- OnSat, 1/10/09, mitalsanghviwrote:

[ishacon]

Dr. Subramanian,

Very interesting write up on shear strength of concrete.
Thanks for the information.

The Paper published in ASCE Structural Journal, Jan 09 issue, which you mention:
Lubell,A.S., E. C. Bentz, and M. P. Collins,Influence of Longitudinal Reinforcement
on One-Way Shear in Slabs and Wide Beams ----

Can this paper be accessed as a soft copy ?
If yes, what is the link ?

Thanks,

VP Agarwal

ISHA CONSULTANTS (P) LTD
NEW DELHI

PH : 011- 2630 1158
(M) 93 1345 2180
(M) 98 6826 2759
ishacon@bol.net.in (ishacon@bol.net.in)
ishacon@rediffmail.com (ishacon@rediffmail.com)