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Proposed REVISION OF IS:456-2000- Inviting Comments
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nandish
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PostPosted: Wed Jan 09, 2013 6:19 pm    Post subject: Re: Proposed REVISION OF IS:456-2000- Inviting Comments Reply with quote

hemal wrote:
Dear Sefi Members,

I hope future revision of IS:456 will include section property modifiers (i.e. for I, A etc) for various structural elements (i.e. column, shear wall, link beam, beam, slab etc of RC & PT) to account for cracking for basic guidelines.

Regards
Hemal Mistry
Surat

On Tue, 8/1/13, Dr. N. Subramanian <forum> wrote:
Quote:

From: Dr. N. Subramanian <forum>
Subject: [SEFI] Proposed REVISION OF IS:456-2000- Inviting Comments
To: general@sefindia.org
Date: Tuesday, 8 January, 2013, 10:00 AM

     Dear All,

I came to know from Mr Sanjay Pant, Director (Civil Engineering)
Bureau of Indian Standards, that they are going to take up the revision of IS 456 soon. Hence our Er Mallick proposed the idea of collecting comments from our SEFIans, which can be passed on to BIS. Hence I am starting this Tread. Please post your comments only in this tread and not in several other places.

Best wishes,
Subramanian
     



     



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nandish
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PostPosted: Wed Jan 09, 2013 6:27 pm    Post subject: Proposed REVISION OF IS:456-2000. Reply with quote

Dear SEFI Members,


As per my opinion it becomes highly important to understand the section property modifiers separately for RC & PT and also not just by using it as any software package inclusions.

As the matter of fact the stiffnesses EI used in an elastic analysis used for strength design should actually represent the stiffnesses of the members immediately before the failure. Hence the alternative values of the moments of inertia given in other international codes were derived for non-pre-stressed members. For pre-stressed members, the moments of inertia may differ depending on the amount, location and type of the reinforcement and the degree of cracking prior to ultimate. The stiffness values for pre-stressed concrete members should include an allowance for the variability of the stiffnesses and it is also recommended in International codes.

Frame analyses normally will be carried out using factored loads, but analyses of deflections, vibrations & serviceability requirements are needed at various service loads i.e. unfactored load levels, to determine the serviceability of the structure.

The moments of inertia of the pre-stress members in the service load analyses should therefore be representative of the degree of cracking at the various service load levels which is highly sensitive. So for Pre-stress Members due care should be taken before suggesting the section property modifiers , because consequently by estimating higher amount of Pre-stressing steel we should not end up on over reinforced Pre-stressed member which eventually may result in upward deflections before the service loads are imposed on it.


Looking for the feedback of my opinion.
-Nandish R. Pethani

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VPandya
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PostPosted: Wed Jan 09, 2013 7:37 pm    Post subject: New revised IS 456-2000 could be comparable to ACI 318-11 Reply with quote

Dear Sefian's,

We need to make sure following topics are covered in new revised IS 456 2000  in as much detail as in Concrete Design based on USA Code ACI 318-11.


1.    Structural Integrity.
2.    Stiffness, concrete properties reduction.
3.    Earthquake Design and Detailing. Chapter-21
4.    Anchor Bolts, ACI 318-11 , Appendix-D



See the second point , " Stiffness reduction for Concrete frame members for analysis and design" . The reduced values based on ACI 318-11 did surprise many of my Indian Engineer  friends. I did worked out the numbers. Here  they are (Following is from my presentation I made some time back, I have a ppt  file but I can not attach here) :  


  Your next question will be What level Of Concrete Cracking for Beams and Columns in a Concrete Frame Analysis to be taken? 50% or 40% of Ig (Gross Moment of Inertia) ?
See my posting on this issue dated 20th March 2012 on the topic "Modeling in SAP-2000-14". My values for both at Service Loads and Factored Loads (Limit State) are based on ACI 318-11 Section 8.7, 8.8.1 and 8.8.2.

I can help you with this problem of "CONCRETE CRACKED SECTION PROPERTIES" to be used in Concrete Frame Analysis in STAAD/PRO or SAP-2000. Recently I myself run in to this problem while reviewing a fellow Engineers Concrete Frame Analysis and Design. This Frame Analysis and Design for an International Project was based on ACI 318-05 . Properties of Concrete Frame analysis were based on Gross Section ( Ig = 1/12X bxd**3) and not on reduced properties of ACI 318-05 section 10.11.1. This was corrected later. A new analysis and design was done.

Point is there still exist some confusion for many engineers on International Projects as to how to meet requirements of ACI 318 code for Concrete Frame Analysis. What is the intent of ACI 318-11 Section 8.7, 8.8.1 and 8.8.2.?
Here is my understanding of Concrete Cracked Section Properties based on ACI 318-11 Section 8.8.1 and 8.8.2 (a).
Cracked Section properties from Section 10.10.4.1:
Modulus of Elasticity Ec = Ec section 8.5.1 (No reduction)
Moment of Inertia of Columns (Iyy and Izz) = 0.7Ig (Ig = Gross Ig = 1/12xbd**3)
No reduction in Ixx (Torsion) and Ax, AY , AZ

Moment of Inertia of Beams (Iyy and Izz) = 0.35Ig (Ig = Gross Ig = 1/12xbd**3)
No reduction in Ixx (Torsion) and Ax, AY , AZ

There are two seperate analysis you will be doing of your 3D Concrete Frame:



1) At Service Load Combinations:-For Frame Drift, Member Deflections and Foundation Pressures (Soil Bearing Stress): Based on section 8.8.1:
a) For Columns Use Iyy and Izz = 1.4X0.7Ig = 0.98Ig = Ig (at Service Load  combinations you can use Ig (uncracked) for Columns.
b) For Beams (Flexure) Use Iyy and Izz = 1.4X0.35Ig = 0.49Ig (say 0.5Ig or 50% of  gross Moment of Inertia for beams. Think of this even at Service Loads analysis  ACI Code wants you use only 50%Ig for Beams in Frame Analysis. This will  change your frame Drift, Member Deflections and may impact your Frame Member  Sizes to get to the allowable Drift, Member Deflections Values. STAAD/PRO Tech.
Reference Manual Section 3.3 has the same values of Concrete Cracked Section  Properties for Beams (50% Ig) for many years.

2) At Factored Load Combinations:-- For Member Design Forces and Reinforcement Design.
a) For Columns use Iyy and Izz = 0.7Ig
No reduction in Ixx (Torsion) and Ax, AY , AZ
b) For Beams (Flexure) use Iyy and Izz = 0.35Ig
No reduction in Ixx (Torsion) and Ax, AY , AZ
If you want Code also allows you to use Iyy and Izz = 0.5Ig for both Columns  and Beams based on section 8.8.2(b).

Point is using Gross Moment of Inertia Ig for Concrete Frame Analysis at Factored Load Combinations is simply wrong. Some of us engineers still have not cought up with this change and use Gross Moment Of Inertias (Ig) for beams at Service Load and Factored Loads. Based on ACI 318 Code we can not and should not do that.


Regards.


Vasudeo Pandya P.E. ; S.E.
Structural Engineer
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Manoharbs_eq
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PostPosted: Thu Jan 10, 2013 4:05 am    Post subject: Reply with quote

Dear Dr.NS sir,

Flat plate is provided In IS code but is not elaborate as in BS. We need to update the code to be little more detailed insight should be included.

Dear sir here in South India now apartments are constructed with Mivan type shuttering with complete walls and slabs integrated as box Rc  structure's, we don't have any specific considerations available yet in IS codes as such provided in ACI.


Rgds
Manohar
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PostPosted: Thu Jan 10, 2013 4:14 am    Post subject: Reply with quote

Column length factor provided in Appendix E of IS 456 shall be revised, Because in Flat slab and flat plate the length factor would be more than 3 very often, there a statement shall be included that P-Delta shall be performed for these type of structures.

P-delta parameters are not included in IS 456 we need to include these parameters and procedure for analysis.



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Manohar
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va
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PostPosted: Thu Jan 10, 2013 5:13 am    Post subject: Proposed REVISION OF IS:456-2000- Inviting Comments Reply with quote

Dear SEFIans,
<![if !supportLists]>1) <![endif]>We should have some minimum width of column like 300mm ( like American code) to improve detailing at beam column junction.( Considering general building beam width is 200 or 230mm) . Column width should be more than beam width for proper detailing.
<![if !supportLists]>2) <![endif]>Maximum column reinforcement 4% is not practical to execute at site. Recommended reinforcement should be about 2.5% to avoid congestion.
<![if !supportLists]>3) <![endif]>A chapter on “Constructability” can be added considering construction aspects of RCC elements. Like special confining reinforcement in columns and beam column junctions, heavy congestion of reinforcement at junctions of beam / column, problems in design of connecting member for coupled shear walls, deep beam construction in layers and stages, several aspects addressing difficulty faced at site by the execution team. Good engineering practices in design and execution.

Hemant Vadalkar
Consulting Engineer Mumbai.
  
From: Dr. N. Subramanian [mailto:forum@sefindia.org]
Sent: Tuesday, January 08, 2013 9:30 PM
To: general@sefindia.org
Subject: [SEFI] Proposed REVISION OF IS:456-2000- Inviting Comments



Dear All,

I came to know from Mr Sanjay Pant, Director (Civil Engineering)
Bureau of Indian Standards, that they are going to take up the revision of IS 456 soon. Hence our Er Mallick proposed the idea of collecting comments from our SEFIans, which can be passed on to BIS. Hence I am starting this Tread. Please post your comments only in this tread and not in several other places.

Best wishes,
Subramanian

Posted via Email
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hemal
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...


Joined: 01 Apr 2008
Posts: 129

PostPosted: Thu Jan 10, 2013 5:14 am    Post subject: Proposed REVISION OF IS:456-2000- Inviting Comments Reply with quote

Dear SEFI members,

It will be very useful to understand purpose of each clause of code if each clause of code is followed by commentary explaining theoretical background, explanation and short example (if necessary) for particular clause. The code may also be used as handbook/manual to some extent. Most of the international codes like ACI, EC etc have such format which is proved to be very usefull.

Actually, All other indian standards related to structural/geotech engg shall have such format for better understanding of user.

Regards
Hemal Mistry
Surat

On Wed, 9/1/13, sunilgurtoo <forum@sefindia.org> wrote:
Quote:

From: sunilgurtoo <forum@sefindia.org>
Subject: [SEFI] Re: Proposed REVISION OF IS:456-2000- Inviting Comments
To: general@sefindia.org
Date: Wednesday, 9 January, 2013, 10:04 AM

           Dear SEFI members,

For the Flat Plat Construction, IS codes should include the use of STUD Rails /Punching Shear Reinforcement which is mostly used as per US codes In us and other parts of the world.
I have seen lot of stuff from internet for the stud rail and punching shear reinforcement technology, but IS codes being the main governing guidelines, it should include the same.
Regards,
Sunil Gurtoo
pune


From: hemal [mailto:forum@sefindia.org]
Sent: 09 January 2013 17:47
To: general@sefindia.org
Subject: [SEFI] Re: Proposed REVISION OF IS:456-2000- Inviting Comments



Dear Sefi Members,

I hope future revision of IS:456 will include section property modifiers (i.e. for I, A etc) for various structural elements (i.e. column, shear wall, link beam, beam, slab etc of RC & PT) to account for cracking for basic guidelines.

Regards
Hemal Mistry
Surat

On Tue, 8/1/13, Dr. N. Subramanian wrote:
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ranjith.12421
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PostPosted: Thu Jan 10, 2013 6:06 am    Post subject: Proposed REVISION OF IS:456-2000- Inviting Comments Reply with quote

Dear SEFIans,


How about Load transfer calculations for RCC Structure(Slab to Beams for (Polygonal, Circular Slabs))


Regards,


RANJITH



On Wed, Jan 9, 2013 at 5:46 PM, hemal <forum@sefindia.org (forum@sefindia.org)> wrote:
[quote]            Dear Sefi Members,

I hope future revision of IS:456 will include section property modifiers (i.e. for I, A etc) for various structural elements (i.e. column, shear wall, link beam, beam, slab etc of RC & PT) to account for cracking for basic guidelines.

Regards
Hemal Mistry
Surat

On Tue, 8/1/13, Dr. N. Subramanian wrote:
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rakeshrp
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PostPosted: Thu Jan 10, 2013 6:20 am    Post subject: Reply with quote

if include clear idea of calculation of shear strength of pile cap as per enhance shear strength then we optimize pile cap depth.

Regards,

Rakesh patel
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SANGEETA WIJ
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Joined: 27 Jun 2012
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PostPosted: Thu Jan 10, 2013 6:50 am    Post subject: Proposed REVISION OF IS:456-2000- Inviting Comments Reply with quote

Dear Mr Mistry
You have raised a very valid point and I also feel the Code should illustrate some examples of a rigid connection, pinned connection, partially fixed connection and so on, at the column-foundation joint as well as a Beam-Column junction. I have checked some designs where the drawings are released with incorrect Joint details which are not corresponding to the assumptions made during analysis. If illustrated, the details will help our engineers to understand them and co-relate with analysis better.

Regards
Sangeeta Wij

From: hemal [mailto:forum@sefindia.org]
Sent: 10 January 2013 11:57
To: general@sefindia.org
Subject: [SEFI] Re: Proposed REVISION OF IS:456-2000- Inviting Comments



Dear SEFI members,

It will be very useful to understand purpose of each clause of code if each clause of code is followed by commentary explaining theoretical background, explanation and short example (if necessary) for particular clause. The code may also be used as handbook/manual to some extent. Most of the international codes like ACI, EC etc have such format which is proved to be very usefull.

Actually, All other indian standards related to structural/geotech engg shall have such format for better understanding of user.

Regards
Hemal Mistry
Surat

On Wed, 9/1/13, sunilgurtoo wrote:
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