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[sefi_admin]

Dear All:


As promised, here is a note by the code drafting team on the Key Ideas being considered for introduction in the Proposed Revision to IS 456. Pl do participate in the Seminar on March 28 2020 (Rescheduled new date to be announced soon)(details are on SEFI website) and be engaged in the process of code drafting!!
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Revision of
IS 456 Code of Practice for Plain and Reinforced Concrete
IS 1343 Code of Practice for Prestressed Concrete
  
  
The proposed Fifth Revision of the Indian Standard IS456 aims to addresses advances made in the state-of-the-art internationally and in the state-of-the-practice in India in design and construction of structural concrete. In particular, it is expected to addresses the significant developments that have taken place over the last two decades in the fields of concrete technology and the durability of concrete structures. Also, over the last four decades, design engineering has seen major changes. Hence, this revision attempts to bring in an improved understanding of structural behavior, some of which have been raised regularly during structural design, peer review and proof-checking of concrete structures in India. This revision is expected to incorporate a number of important changes.
  
The salient changes in the draft under consideration are:
(1)  The provisions now are required to address three types of concretes, namely Plain, Reinforced and Prestressed Concretes. As a consequence, the title of the unified standard is proposed to be revised as the Indian Standard Code of Practice for Structural Concrete.
(2)  The basis of design will be elaborated. The draft standard now requires concrete structures to be designed for 6 limit states, namely Safety, Serviceability, Durability, Robustness, Integrity, and Restorability. Each limit state is deemed to have been designed for if the structural design is demonstrated to meet the requirements laid down in the standard.
(3)  High strength concretes and reinforcing steels have been considered in the drafting of the provisions in this revision.
(4)  In general, the basic principles of design are proposed to be retained. Axial and flexural capacities are based on strain considerations, and shear and torsion capacities on strength considerations.
(5)  In the Limit State of Safety, the definition of design strength in flexure of a concrete member is proposed to be revised from that corresponding to secondary compression failure of the member to that corresponding to reaching limiting strains.
(6)  The concept of design life is expected to be introduced quantitatively.
(7)  Provisions related to serviceability, durability and fire resistance are expected to be harmonized and rationalized.
(  The drafting is completely new with different and additional chapters. Also, the nomenclature is being changed now to reflect the unfactored, factored and overstrength demands and capacities of concrete members.
(9)  The commentaries of the clauses of the fifth revision are being prepared alongside to give insights into the bases of the new provisions.


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best regards,


SEFI Admin

Posted via Email

[Dr. N. Subramanian]

Dear Er Alpa

First of all I appreciate you for organizing a seminar on the Proposed Revision to IS 456 and IS 1343 by the Revision committee  on March 28 2020.

After going through the proposed revisions, I appreciate the Revision committee for taking pains to do several fundamental revisions. Very happy to note that the committee is considering clubbing RC and  Prestressed concrete like ACI 318. It will be better to bring the clauses of IS 13920 also into the code.

I request the committee to include Sustainability provisions also in the code. What they are meaning by Restorability?


Good to note that High strength concretes and High strength reinforcing steels will also be considered.  Current code has rectangular parabolic block for concrete. Can they make it an equivalent rectangular stress block,similar to that used in ACI 318, which will simplify the calculations? High Strength concrete will anyhow will have triangular stress block. Use of High strength rebars as shear reinforcement could also be considered.

Very glad that they are  including the commentaries of the clauses of the fifth revision which will give insights into the clauses of the new provisions.

The present IS 456 code provisions are based on tests made on concretes having strength less than 40 MPa and hence while including HSC, many provisions will change.


I request them to make the code simple and user friendly and not make it complicated.


I will not be in a position to attend the Seminar on March 28th . But I hope other members will attend and make it a fruitful exercise.

Warm regards
Subramanian

[alpa_sheth]

Dear Dr Subramanian,

Thanks much for your kind words. Your comments are deeply appreciated and will be shared. We shall miss you at the seminar. We hope to be able to  share the proceedings in some form on SEFI at  an early date.

For those of you in India and specially in Mumbai and close to it (Pune, Surat, Nashik, Nagpur, Baroda, Ahmedabad, Hyderabad, Bangalore, Delhi and anywhere in India), this a golden opportunity to participate and make your voice heard in the process of code revision of IS 456. Kindly note that  seats are fast filling up and so secure your registration at the earliest to avoid disappointment.

Best regards,
Alpa

[N. Prabhakar]

Dear Sefians,

From the sneak preview of the proposed revisions of the Code IS 456, it would no doubt be a complicated code as it considers 6 limit-state conditions, leading to more cases of calculations, instead of 2 conditions at present.  Besides, the code is allowing the use of high strength reinforcement bars like fy 550 which are not advisable for ductility requirements in earthquake-resistant structures and when more than 70% of our cities are in Seismic Zone III and above, requiring ductile design.  

By including the subject of Prestressed Concrete in the code, it would make the code voluminous and pricey too.  Except for concrete bridges, Prestressed Concrete is hardly used in India for other forms of construction.  Besides, for bridges IRC code mostly governs the design.  Hence, the inclusion of Prestressed Concrete in IS 456 code is an unnecessary and wasteful effort by BIS.  Let us not do it because ACI or other international codes are doing it.  

The new code should include the provisions of IS 13920 for ductile design and detailing as I said earlier that  more than 70% of our cities are in Seismic Zone III and above, requiring ductile design and detailing.

BIS has to do simultaneous publication of an  Explanatory Handbook like SP : 24 and Design Aids like SP 16, along with the publication of the new revised code. It may take few more months to do them, but it would be a worthy effort. If it is not done, the users of the new code will be left high and dry, leading to wrong usage of the code.

I trust that the code committee will consider the above points in the formation of the new code.

With best wishes,

N. Prabhakar
Chartered Structural Engineer
Vasai (E), Pin 401 208

[N. Prabhakar]

Dear Sefians,

In continuation of my posting in this forum on 5th March, 2020, I wouild like to add the following comment on the proposed revision of IS 456:

The new revised code should include the provisions of the present IS 3370 for liquid-retaining structures, as many underground water tanks and overhead water towers are built in the country.  

These provisions in IS 456 would benefit many structural engineers who are involved in the design of such liquid-retaining structures.

With best wishes,

Yours truly,

N. Prabhakar
Chartered Structural Enginner
Vasai (E), Pin 401 208

[BharadhwajMaitreya]

Dear All,

Please Explain this Clause from IS 16700-2016


5.3 Storey Stiffness and Strength
Parameters influencing stiffness and strength of the
building should be so proportioned, that the following
are maintained:
a) Lateral translational stiffness of any storey shall
not be less than 70 percent of that of the storey
above.



On Tue, Feb 25, 2020 at 7:56 PM sefi_admin <forum@sefindia.org (forum@sefindia.org)> wrote: