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Welcome to e-conference on flat slabs
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dcrai
E-Conference Moderator


Joined: 26 Jan 2003
Posts: 9

PostPosted: Sun Dec 21, 2008 8:52 pm    Post subject: Welcome to e-conference on flat slabs Reply with quote

Dear Colleagues,

A hearty welcome to you to the e-conference on flat slabs at SEFI!
Flat slab structures have become a common sight in our neighbourhood.
However, the recent past failures of flat slab structures have underlined
the need for reviewing the current design and construction practices. This
is amply evident from the issues that have been discussed in the SEFI
forum regarding flat slabs in the recent past and the discussers felt a
more focused discussion of issues related to flat slabs. For this very
same reason, we feel that the timing of the E-Conference could have never
been better.

As we know, the use of flat slabs, in India and around the world, has
increased in the recent past. The factors that could be attributed are
increased customer requirements for open office space (long span
structures) as well as speedier construction and the better understanding
of the behaviour of the flat slab under gravity loads. But it is still a
matter of concern, when flat slabs are subjected to seismic actions as
evidenced from their performance in the past earthquakes and in the
laboratory tests. In addition, problems associated with the current
construction practices of flat slabs, especially post-tensioned types,
need to be reviewed in order to prevent failures during construction and
prevent progressive collapse, which is typical in flat slab structures.
This issue becomes even more critical as the current IS codes are silent
about it.

We are sure that you too have certain expertise/experience or queries
regarding behaviour and design of flat slabs which can be shared and
debated during this E-Conference. Some issues which frequently come up for
discussion are: (1) Ways and means by which the punching shear problem can
be avoided, (2) Methods of reinforcement detailing for satisfactory
behaviour under seismic actions, (3) Problems associated with the imposed
lateral drift along with gravity loads on the slab column connection and
the current construction practices in India, and (6) Need  to ensure
robustness/integrity of the system, by way of requiring minimum lateral
load resistance requirement etc.

We are sure that your views and queries would be of great help in
understanding the various issues related to flat slabs. Those in the know
of design and construction practices abroad are requested to share their
knowledge and experience/expertise. We expect that discussions during the
e-Conference will be healthy, non-malicious, respectful and free from
commercialism. Though we believe that no moderation is the best form of
moderation, we will come in to help the discussion whenever necessary.
Welcome to the e-conference once again and looking forward to your
valuable participation,

Durgesh Rai & Manmohan Kalgal, Moderators

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vaibhavgoyal2
SEFI Member
SEFI Member


Joined: 12 Jun 2008
Posts: 7

PostPosted: Mon Dec 22, 2008 3:13 am    Post subject: Welcome to e-conference on flat slabs Reply with quote

hi..

iam structural engineer from delhi working in dubai
its great to hear from you..
i will definately be in touch with you as we have a lot of flat slab construction over here. please do post me something related to design o =f shear walls and make me in loop for any technical discussion.


On Mon, Dec 22, 2008 at 4:07 AM, dcrai <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
  Dear Colleagues,

A hearty welcome to you to the e-conference on flat slabs at SEFI!
Flat slab structures have become a common sight in our neighbourhood.
However, the recent past failures of flat slab structures have underlined
the need for reviewing the current design and construction practices. This
is amply evident from the issues that have been discussed in the SEFI
forum regarding flat slabs in the recent past and the discussers felt a
more focused discussion of issues related to flat slabs. For this very
same reason, we feel that the timing of the E-Conference could have never
been better.

As we know, the use of flat slabs, in India and around the world, has
increased in the recent past. The factors that could be attributed are
increased customer requirements for open office space (long span
structures) as well as speedier construction and the better understanding
of the behaviour of the flat slab under gravity loads. But it is still a
matter of concern, when flat slabs are subjected to seismic actions as
evidenced from their performance in the past earthquakes and in the
laboratory tests. In addition, problems associated with the current
construction practices of flat slabs, especially post-tensioned types,
need to be reviewed in order to prevent failures during construction and
prevent progressive collapse, which is typical in flat slab structures.
This issue becomes even more critical as the current IS codes are silent
about it.

We are sure that you too have certain expertise/experience or queries
regarding behaviour and design of flat slabs which can be shared and
debated during this E-Conference. Some issues which frequently come up for
discussion are: (1) Ways and means by which the punching shear problem can
be avoided, (2) Methods of reinforcement detailing for satisfactory
behaviour under seismic actions, (3) Problems associated with the imposed
lateral drift along with gravity loads on the slab column connection and
the current construction practices in India, and (6) Need to ensure
robustness/integrity of the system, by way of requiring minimum lateral
load resistance requirement etc.

We are sure that your views and queries would be of great help in
understanding the various issues related to flat slabs. Those in the know
of design and construction practices abroad are requested to share their
knowledge and experience/expertise. We expect that discussions during the
e-Conference will be healthy, non-malicious, respectful and free from
commercialism. Though we believe that no moderation is the best form of
moderation, we will come in to help the discussion whenever necessary.
Welcome to the e-conference once again and looking forward to your
valuable participation,

Durgesh Rai & Manmohan Kalgal, Moderators








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sdec.in
Silver Sponsor
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Joined: 26 Jan 2003
Posts: 473

PostPosted: Mon Dec 22, 2008 4:32 am    Post subject: Welcome to e-conference on flat slabs Reply with quote

Thanks Dr Rai and Dr Kalgal and welcome to the econference
I have been observing a lot of modern Flat slab construction in NCR region and feel the likely seismic performance of these structures maybe suspect unless the correct design/ detailing issues are understood by the designers.I have always stuck to the principle of giving stiff peripheral beams and a min of 3 bays each for such systems in EQ zones.Pl comment and give explicit tips on correct detailing in zones IV and V.
Regards and best wishes
Sangeeta Wij
Quote:
----- Original Message -----
From: dcrai (forum@sefindia.org)
To: econf@sefindia.org (econf@sefindia.org)
Sent: 22 December, 2008 5:37 AM
Subject: [ECONF] Welcome to e-conference on flat slabs


Dear Colleagues,

A hearty welcome to you to the e-conference on flat slabs at SEFI!
Flat slab structures have become a common sight in our neighbourhood.
However, the recent past failures of flat slab structures have underlined
the need for reviewing the current design and construction practices. This
is amply evident from the issues that have been discussed in the SEFI
forum regarding flat slabs in the recent past and the discussers felt a
more focused discussion of issues related to flat slabs. For this very
same reason, we feel that the timing of the E-Conference could have never
been better.

As we know, the use of flat slabs, in India and around the world, has
increased in the recent past. The factors that could be attributed are
increased customer requirements for open office space (long span
structures) as well as speedier construction and the better understanding
of the behaviour of the flat slab under gravity loads. But it is still a
matter of concern, when flat slabs are subjected to seismic actions as
evidenced from their performance in the past earthquakes and in the
laboratory tests. In addition, problems associated with the current
construction practices of flat slabs, especially post-tensioned types,
need to be reviewed in order to prevent failures during construction and
prevent progressive collapse, which is typical in flat slab structures.
This issue becomes even more critical as the current IS codes are silent
about it.

We are sure that you too have certain expertise/experience or queries
regarding behaviour and design of flat slabs which can be shared and
debated during this E-Conference. Some issues which frequently come up for
discussion are: (1) Ways and means by which the punching shear problem can
be avoided, (2) Methods of reinforcement detailing for satisfactory
behaviour under seismic actions, (3) Problems associated with the imposed
lateral drift along with gravity loads on the slab column connection and
the current construction practices in India, and (6) Need to ensure
robustness/integrity of the system, by way of requiring minimum lateral
load resistance requirement etc.

We are sure that your views and queries would be of great help in
understanding the various issues related to flat slabs. Those in the know
of design and construction practices abroad are requested to share their
knowledge and experience/expertise. We expect that discussions during the
e-Conference will be healthy, non-malicious, respectful and free from
commercialism. Though we believe that no moderation is the best form of
moderation, we will come in to help the discussion whenever necessary.
Welcome to the e-conference once again and looking forward to your
valuable participation,

Durgesh Rai & Manmohan Kalgal, Moderators







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RAHULGEHLOT2009
SEFI Regulars
SEFI Regulars


Joined: 19 Sep 2008
Posts: 28

PostPosted: Mon Dec 22, 2008 5:37 am    Post subject: E-conference on flat slabs Reply with quote

Sir, I have seen many structure having stiff peripheral beams, but some designers provide drop slab and some prefer not to provide drop. Whether drop panel can be avoided in ZONE IV or V? Please advice.
Regards,
Rahul Gehlot
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ykalamkar
...
...


Joined: 26 Jan 2003
Posts: 108
Location: Nagpur

PostPosted: Mon Dec 22, 2008 6:50 am    Post subject: Welcome to e-conference on flat slabs Reply with quote

Thanks sir,
I would like to know more about the sunk and cutouts in the flat slab. In one case, there is 3 span flat slab and middle portion is to be sunken by 50 or 150 mm only. Is it possible to sunk the central part at 45 deg. like this  

Is it possible to provide cutouts in column strip?  
Regards
Yogesh Kalamkar

From: dcrai [mailto:forum@sefindia.org]
Sent: Monday, December 22, 2008 5:37 AM
To: econf@sefindia.org
Subject: [ECONF] Welcome to e-conference on flat slabs



Dear Colleagues,

A hearty welcome to you to the e-conference on flat slabs at SEFI!
Flat slab structures have become a common sight in our neighbourhood.
However, the recent past failures of flat slab structures have underlined
the need for reviewing the current design and construction practices. This
is amply evident from the issues that have been discussed in the SEFI
forum regarding flat slabs in the recent past and the discussers felt a
more focused discussion of issues related to flat slabs. For this very
same reason, we feel that the timing of the E-Conference could have never
been better.

As we know, the use of flat slabs, in India and around the world, has
increased in the recent past. The factors that could be attributed are
increased customer requirements for open office space (long span
structures) as well as speedier construction and the better understanding
of the behaviour of the flat slab under gravity loads. But it is still a
matter of concern, when flat slabs are subjected to seismic actions as
evidenced from their performance in the past earthquakes and in the
laboratory tests. In addition, problems associated with the current
construction practices of flat slabs, especially post-tensioned types,
need to be reviewed in order to prevent failures during construction and
prevent progressive collapse, which is typical in flat slab structures.
This issue becomes even more critical as the current IS codes are silent
about it.

We are sure that you too have certain expertise/experience or queries
regarding behaviour and design of flat slabs which can be shared and
debated during this E-Conference. Some issues which frequently come up for
discussion are: (1) Ways and means by which the punching shear problem can
be avoided, (2) Methods of reinforcement detailing for satisfactory
behaviour under seismic actions, (3) Problems associated with the imposed
lateral drift along with gravity loads on the slab column connection and
the current construction practices in India, and (6) Need to ensure
robustness/integrity of the system, by way of requiring minimum lateral
load resistance requirement etc.

We are sure that your views and queries would be of great help in
understanding the various issues related to flat slabs. Those in the know
of design and construction practices abroad are requested to share their
knowledge and experience/expertise. We expect that discussions during the
e-Conference will be healthy, non-malicious, respectful and free from
commercialism. Though we believe that no moderation is the best form of
moderation, we will come in to help the discussion whenever necessary.
Welcome to the e-conference once again and looking forward to your
valuable participation,

Durgesh Rai & Manmohan Kalgal, Moderators

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PostPosted: Mon Dec 22, 2008 8:41 am    Post subject: Welcome to e-conference on flat slabs Reply with quote

Welcome Sir

How are you?

Its good that we have a very interesting subject… in the conference

My question is that, I’ve observed in most of the Smalltime builders just do one Panel of 12.0m by 10.0m, Site being some 15.0m by 15.0m How good or viable it is???


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P please consider the environment - do you really need to print this email?




From: ykalamkar [mailto:forum@sefindia.org]
Sent: Monday, December 22, 2008 12:31 PM
To: econf@sefindia.org
Subject: [ECONF] Re: Welcome to e-conference on flat slabs



Thanks sir,
I would like to know more about the sunk and cutouts in the flat slab. In one case, there is 3 span flat slab and middle portion is to be sunken by 50 or 150 mm only. Is it possible to sunk the central part at 45 deg. like this

Is it possible to provide cutouts in column strip?
Regards
Yogesh Kalamkar

From: dcrai [mailto:forum@sefindia.org]
Sent: Monday, December 22, 2008 5:37 AM
To: econf@sefindia.org (econf@sefindia.org)
Subject: [ECONF] Welcome to e-conference on flat slabs



Dear Colleagues,

A hearty welcome to you to the e-conference on flat slabs at SEFI!
Flat slab structures have become a common sight in our neighbourhood.
However, the recent past failures of flat slab structures have underlined
the need for reviewing the current design and construction practices. This
is amply evident from the issues that have been discussed in the SEFI
forum regarding flat slabs in the recent past and the discussers felt a
more focused discussion of issues related to flat slabs. For this very
same reason, we feel that the timing of the E-Conference could have never
been better.

As we know, the use of flat slabs, in India and around the world, has
increased in the recent past. The factors that could be attributed are
increased customer requirements for open office space (long span
structures) as well as speedier construction and the better understanding
of the behaviour of the flat slab under gravity loads. But it is still a
matter of concern, when flat slabs are subjected to seismic actions as
evidenced from their performance in the past earthquakes and in the
laboratory tests. In addition, problems associated with the current
construction practices of flat slabs, especially post-tensioned types,
need to be reviewed in order to prevent failures during construction and
prevent progressive collapse, which is typical in flat slab structures.
This issue becomes even more critical as the current IS codes are silent
about it.

We are sure that you too have certain expertise/experience or queries
regarding behaviour and design of flat slabs which can be shared and
debated during this E-Conference. Some issues which frequently come up for
discussion are: (1) Ways and means by which the punching shear problem can
be avoided, (2) Methods of reinforcement detailing for satisfactory
behaviour under seismic actions, (3) Problems associated with the imposed
lateral drift along with gravity loads on the slab column connection and
the current construction practices in India, and (6) Need to ensure
robustness/integrity of the system, by way of requiring minimum lateral
load resistance requirement etc.

We are sure that your views and queries would be of great help in
understanding the various issues related to flat slabs. Those in the know
of design and construction practices abroad are requested to share their
knowledge and experience/expertise. We expect that discussions during the
e-Conference will be healthy, non-malicious, respectful and free from
commercialism. Though we believe that no moderation is the best form of
moderation, we will come in to help the discussion whenever necessary.
Welcome to the e-conference once again and looking forward to your
valuable participation,

Durgesh Rai & Manmohan Kalgal, Moderators  





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gorhemant
SEFI Member
SEFI Member


Joined: 27 Jun 2008
Posts: 11

PostPosted: Mon Dec 22, 2008 9:33 am    Post subject: Welcome to e-conference on flat slabs Reply with quote

Subject : Post - Tension Flat Introduction

Reinforced Concrete and Post -Tension Flat slab system are very common floor system in Middle East region. The most of the part of Middle East region falls under seismic zone 2A as per UBC97.
The Post-Tensioned Slabs are designed as per guidelines given in Technical Report 43 from Concrete Society. This is specilised document on Post-Tension element design in Buildings. Othe Standards commenly used are BS 8110 and ACI318.

The BS8110 classifies Post-Tension Elements in three class, based on tensile stress in concrete during service.
One Can find similar classification in ACI, But with different name, they Classify Class U (uncracked), Class C ( cracked) and Class T (Transition Between C and U).
ACI restricts tensile stresses in slab to 0.5xSQRT (fc') ( where fc' is cylinder strength).
Most of the PT flat slab software support FEM analysis along with Post-Tension Cable Layout. The stresses are checked for design strips / design sections ( integration of results along section, similar to assigning Pier Labels / Spandrels labels in ETABS) are generated in orthogonal directions to check service stresses at transfer and service. The design sections are checked for Ultimate Flexural strength and of course Punching shear check around columns.
In TR43 allows Partial Prestrsessing, It means the Un-tensioned reinforcement is added to PT cables to restrict crack width limits.
Few of widly used PT flat slab analysis and design tools are

CEDRU 5
ADAPT Floor Pro / ADAPT PT
RAM Concept
and recently CSI added Post-Tension Objects in SAFE Version 12

thanks and regards,


Hemant Gor
M.Tech (Structure) (IITB)
Post-Tension Design Specialist
gorhemant@gmail.com (gorhemant@gmail.com)
On Mon, Dec 22, 2008 at 4:07 AM, dcrai <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
  Dear Colleagues,

A hearty welcome to you to the e-conference on flat slabs at SEFI!
Flat slab structures have become a common sight in our neighbourhood.
However, the recent past failures of flat slab structures have underlined
the need for reviewing the current design and construction practices. This
is amply evident from the issues that have been discussed in the SEFI
forum regarding flat slabs in the recent past and the discussers felt a
more focused discussion of issues related to flat slabs. For this very
same reason, we feel that the timing of the E-Conference could have never
been better.

As we know, the use of flat slabs, in India and around the world, has
increased in the recent past. The factors that could be attributed are
increased customer requirements for open office space (long span
structures) as well as speedier construction and the better understanding
of the behaviour of the flat slab under gravity loads. But it is still a
matter of concern, when flat slabs are subjected to seismic actions as
evidenced from their performance in the past earthquakes and in the
laboratory tests. In addition, problems associated with the current
construction practices of flat slabs, especially post-tensioned types,
need to be reviewed in order to prevent failures during construction and
prevent progressive collapse, which is typical in flat slab structures.
This issue becomes even more critical as the current IS codes are silent
about it.

We are sure that you too have certain expertise/experience or queries
regarding behaviour and design of flat slabs which can be shared and
debated during this E-Conference. Some issues which frequently come up for
discussion are: (1) Ways and means by which the punching shear problem can
be avoided, (2) Methods of reinforcement detailing for satisfactory
behaviour under seismic actions, (3) Problems associated with the imposed
lateral drift along with gravity loads on the slab column connection and
the current construction practices in India, and (6) Need to ensure
robustness/integrity of the system, by way of requiring minimum lateral
load resistance requirement etc.

We are sure that your views and queries would be of great help in
understanding the various issues related to flat slabs. Those in the know
of design and construction practices abroad are requested to share their
knowledge and experience/expertise. We expect that discussions during the
e-Conference will be healthy, non-malicious, respectful and free from
commercialism. Though we believe that no moderation is the best form of
moderation, we will come in to help the discussion whenever necessary.
Welcome to the e-conference once again and looking forward to your
valuable participation,

Durgesh Rai & Manmohan Kalgal, Moderators








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ykalamkar
...
...


Joined: 26 Jan 2003
Posts: 108
Location: Nagpur

PostPosted: Mon Dec 22, 2008 11:03 am    Post subject: Welcome to e-conference on flat slabs Reply with quote

I think sketch is not visible in this mail. I am attaching the section showing sunk portion along with slab propotion.
Regards
Yogesh  
From: ykalamkar [mailto:forum@sefindia.org]
Sent: Monday, December 22, 2008 12:31 PM
To: econf@sefindia.org
Subject: [ECONF] Re: Welcome to e-conference on flat slabs



Thanks sir,
I would like to know more about the sunk and cutouts in the flat slab. In one case, there is 3 span flat slab and middle portion is to be sunken by 50 or 150 mm only. Is it possible to sunk the central part at 45 deg. like this

Is it possible to provide cutouts in column strip?
Regards
Yogesh Kalamkar

From: dcrai [mailto:forum@sefindia.org]
Sent: Monday, December 22, 2008 5:37 AM
To: econf@sefindia.org (econf@sefindia.org)
Subject: [ECONF] Welcome to e-conference on flat slabs



Dear Colleagues,

A hearty welcome to you to the e-conference on flat slabs at SEFI!
Flat slab structures have become a common sight in our neighbourhood.
However, the recent past failures of flat slab structures have underlined
the need for reviewing the current design and construction practices. This
is amply evident from the issues that have been discussed in the SEFI
forum regarding flat slabs in the recent past and the discussers felt a
more focused discussion of issues related to flat slabs. For this very
same reason, we feel that the timing of the E-Conference could have never
been better.

As we know, the use of flat slabs, in India and around the world, has
increased in the recent past. The factors that could be attributed are
increased customer requirements for open office space (long span
structures) as well as speedier construction and the better understanding
of the behaviour of the flat slab under gravity loads. But it is still a
matter of concern, when flat slabs are subjected to seismic actions as
evidenced from their performance in the past earthquakes and in the
laboratory tests. In addition, problems associated with the current
construction practices of flat slabs, especially post-tensioned types,
need to be reviewed in order to prevent failures during construction and
prevent progressive collapse, which is typical in flat slab structures.
This issue becomes even more critical as the current IS codes are silent
about it.

We are sure that you too have certain expertise/experience or queries
regarding behaviour and design of flat slabs which can be shared and
debated during this E-Conference. Some issues which frequently come up for
discussion are: (1) Ways and means by which the punching shear problem can
be avoided, (2) Methods of reinforcement detailing for satisfactory
behaviour under seismic actions, (3) Problems associated with the imposed
lateral drift along with gravity loads on the slab column connection and
the current construction practices in India, and (6) Need to ensure
robustness/integrity of the system, by way of requiring minimum lateral
load resistance requirement etc.

We are sure that your views and queries would be of great help in
understanding the various issues related to flat slabs. Those in the know
of design and construction practices abroad are requested to share their
knowledge and experience/expertise. We expect that discussions during the
e-Conference will be healthy, non-malicious, respectful and free from
commercialism. Though we believe that no moderation is the best form of
moderation, we will come in to help the discussion whenever necessary.
Welcome to the e-conference once again and looking forward to your
valuable participation,

Durgesh Rai & Manmohan Kalgal, Moderators  





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prof.arc
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Joined: 26 Jan 2003
Posts: 703

PostPosted: Tue Dec 23, 2008 1:57 am    Post subject: Welcome to e-conference on flat slabs Reply with quote

Dear Prof. Durgesh Rai,
I am quite sure that this econf managed by you would be a success.

Probably, we have sufficient analytical tools to find out distribution of forces on the column - slab junction. But it is a matter of how it can be engineered that the transfer indeed takes place as required by the analysis.

It is most likely from a statistical point of view, all such buildings may not be subjected to earthquake loads and hence if the structure stands after the shuttering is removed it would vindicate the design.

The points that need attention for estimating earthquake forces is the Response Reduction Factor. I feel definitely that it cannot be 5 but far less.

The infill walls round the lift well will play a substantial role - hence details of transfer of forces from the slab to the lift core becomes crucial.

I hope the architects would have a rethink on exterior columns around the periphery of building and permit a grid work of beams connecting the columns. Also, exterior shear walls at the four corners. Then, such constructions would be safe even in Zone V.

I would suggest that SERC-Chennai tests such construction - vary joint details of slabs and columns - on their huge shake table. Find out R value experimentally

Best wishes
Sincerely
ARC


On Mon, Dec 22, 2008 at 5:37 AM, dcrai <forum@sefindia.org (forum@sefindia.org)> wrote:

Quote:
           Dear Colleagues,

A hearty welcome to you to the e-conference on flat slabs at SEFI!
Flat slab structures have become a common sight in our neighbourhood.

Durgesh Rai & Manmohan Kalgal, Moderators



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mkalgal
Silver Sponsor
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Joined: 26 Jan 2003
Posts: 54

PostPosted: Wed Dec 24, 2008 6:09 pm    Post subject: Reply with quote

Dear Sangeeta

I agree fully with you.

In flat slab or flat plate systems, there is significant transfer of  moment, shear and torsion at edge and corner column juntions with the slabs. The exact mechanism/interaction is quite a grey area inspite of lot of research (and PhD degrees!).

In our enthusiasm to provide economical(!) sections, we sometimes give a go-by to several critical issues and most often get away with it. It is only when a failure occurs that the "blame game" starts!

Detailing and construction procedures are two very important areas where all meticulous and accurate calculations with most sophisticated softwares can go haywire.

I once came across a flat slab construction where the total slab thickness was cast in two layers with a clear laitance layer in between. How would this slab behave in two-way shear? It is frightening. I have seen people casting the drop panels(upto the bottom level of slabs)  in the first pass and the top layer along with rest of the slab.

As for the continuation of bottom steel at support(to act as a safety net), I have seen many engineers arguing that it is a waste since it is near the middle of the slab if panel drop thickness is considered(our Fig. 16 of IS 456 doesn't come to our rescue!).

As for PT flat slabs it is another story altogether. Draft revison of IS 1343 was under circulation. I don't know if we could suggest any change in this before it is printed. I am attaching it with the hope that it generates good suggestions (and heated debate)

regards to all

Kalgal



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