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Cost implications between RC slab and Flat /PT slab
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Sampath
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Joined: 30 Dec 2008
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PostPosted: Wed Dec 31, 2008 5:40 am    Post subject: Cost implications between RC slab and Flat /PT slab Reply with quote

Hi All

It is becoming popular now using Flat slab and PT slab in India and I am curious to know the cost to benfit ratio between RC slab and Flat/PT slab.

I have not done a real time design of both and compared myself, so I appriciate to hear from someone who had already come across with this.

1. Can we use flat slab, especially PT slab in a residential building to reduce cost, preferably using more span length as PT slab can offer more in serviceability conditions.

2. What is the minimum concrete strength that is practical in PT slab

3. What would be the rought cost difference / unit area between using RC slab and PT slab.

Sampath
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Dr. N. Subramanian
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PostPosted: Wed Dec 31, 2008 10:41 pm    Post subject: Cost implications between RC slab and Flat /PT slab Reply with quote

Dear Mr. Sampath,

I have designed only a few flat slab structures, made of RCC. They are for commercial buildings. Of course they are cheaper than beam-slab construction, due to the simplified form work. But I feel that they may not be useful for residential buildings, because the plan will not be uniform. PT slabs may be economical for large projects only, as we may have to pay for the PT contractors, separately.

Best wishes
Subramanian

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





--- On Wed, 12/31/08, Sampath <forum@sefindia.org> wrote:
Quote:
From: Sampath <forum@sefindia.org>
Subject: [ECONF] Cost implications between RC slab and Flat /PT slab
To: econf@sefindia.org
Date: Wednesday, December 31, 2008, 11:10 AM

Hi All

It is becoming popular now using Flat slab and PT slab in India and I am curious to know the cost to benfit ratio between RC slab and Flat/PT slab.

I have not done a real time design of both and compared myself, so I appriciate to hear from someone who had already come across with this.

1. Can we use flat slab, especially PT slab in a residential building to reduce cost, preferably using more span length as PT slab can offer more in serviceability conditions.

2. What is the minimum concrete strength that is practical in PT slab

3. What would be the rought cost difference / unit area between using RC slab and PT slab.

Sampath
     



     


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rbchopda
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Joined: 30 Aug 2008
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PostPosted: Thu Jan 01, 2009 2:07 pm    Post subject: Cost implications between RC slab and Flat /PT slab Reply with quote

Dear Sir,
I do not agree with your statement that flat slab structures are more economical than beam-slab structures.
Main consideration in using flat slab type structure for commercial buildings is because of height limitation from
municipal bye-laws. As there is a heavy reinforcement requirement in flat-type structures compaired to beam-slab structure.

Regards
er.rbchopda@rediffmail.com (er.rbchopda@rediffmail.com)


On Thu, Jan 1, 2009 at 8:26 AM, drnsmani <forum@sefindia.org (forum@sefindia.org)> wrote:
[quote]  Dear Mr. Sampath,

I have designed only a few flat slab structures, made of RCC. They are for commercial buildings. Of course they are cheaper than beam-slab construction, due to the simplified form work. But I feel that they may not be useful for residential buildings, because the plan will not be uniform. PT slabs may be economical for large projects only, as we may have to pay for the PT contractors, separately.

Best wishes
Subramanian

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





--- On Wed, 12/31/08, Sampath wrote:
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PostPosted: Thu Jan 01, 2009 4:04 pm    Post subject: Cost implications between RC slab and Flat /PT slab Reply with quote

Dear Mr. Chopda,

In countries like USA, where labour costs are high, simplification of form work results in low labour costs and minimum construction time. When you consider the total cost you have to take into account many factors including cost of materials, cost of labour, cost of formwork, maintenance cost, etc. The cost of the particular system is also dependent on the selected span. For longer spans (say 25-30 feet) PT flat slabs will be more economical than any other slab system.

More deatails about the ecnomics of slab systems is given in the following paper:
Fintel, M., and Ghosh, S.K., Economics of Long span concrete slab systems for office buildings- A Survey, Concrete International, Feb. 83, pp.21-34

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





--- On Thu, 1/1/09, rbchopda <forum@sefindia.org> wrote:
Quote:
From: rb <forum@sefindia.org>
Subject: [ECONF] Re: Cost implications between RC slab and Flat /PT slab
To: econf@sefindia.org
Date: Thursday, January 1, 2009, 8:15 PM

Dear Sir,
I do not agree with your statement that flat slab structures are more economical than beam-slab structures.
Main consideration in using flat slab type structure for commercial buildings is because of height limitation from
municipal bye-laws. As there is a heavy reinforcement requirement in flat-type structures compaired to beam-slab structure.

Regards
er.rbchopda@rediffmail.com (er.rbchopda@rediffmail.com) (er.rbchopda@rediffmail.com (er.rbchopda@rediffmail.com))


On Thu, Jan 1, 2009 at 8:26 AM, drnsmani forum@sefindia.org)> wrote:
Quote:
Dear Mr. Sampath,

I have designed only a few flat slab structures, made of RCC. They are for commercial buildings. Of course they are cheaper than beam-slab construction, due to the simplified form work. But I feel that they may not be useful for residential buildings, because the plan will not be uniform. PT slabs may be economical for large projects only, as we may have to pay for the PT contractors, separately.

Best wishes
Subramanian

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





--- On Wed, 12/31/08, Sampath wrote:
--auto removed--
     



     




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mkalgal
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Joined: 26 Jan 2003
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PostPosted: Thu Jan 01, 2009 7:03 pm    Post subject: Reply with quote

Dear SEFIANs
As rightly mentioned by Dr. Subramanian, the economics are different in developed contries (where labor is relatively costly) and developing countries (where labour is relatively cheap, but any unconventional method is deemed costly). As long as the technologies are not demystified, the technology providers tend to charge more (like it happened initially with PT Slabs in India).

I am still of the opinion that RC framed buildings tend to be cheaper in India as compared to RC flat slabs for the normal spans of 8m to 11m for commerical/IT buildings. But as said earlier in one of my mails, Flat Slabs are chosen for other reasons like headroom, flexibility in internal planning of partitions(you have no beams to hide you see!), speed of construction etc.

Once a flat slab system is chosen for whatever reasons, we, in my previous company had successfully proved that PT flat slabs are equal in cost to an RC flat slab if not cheaper by upto 10 percent. This is true for spans between 10m and 14m and depends on several aspects like LL to DL ratio, number of spans in each direction, depth of panel drop allowed by the architects, column sizes and so on.

Additionally we have higher grade concrete(leading to improved durability generally) and better control over short and long term deflections.

The general steps in cost comparison(between RC and PT flat slabs) is as follows :
1. Calculate the volume of concrete and steel required for RC flat slab per sqm.
2. Find the cost of concrete/sqm. (generally M20 or M25) and cost of rebar/sqm.
3. Calculate the volume of concrete and steel required for PT flat slab per sqm.
4. Calculate the cost of concrete/sqm. (generally M35 and hence a little costlier --but volume of concrete would be slightly lesser) and cost of rebar/sqm. (which would be substantilly less than that req. for RC flat slab)
5. Add the cost of prestressing (which is given by the PT agency in Rs./sqm).
6. Cost of formwork is same for RC and PT flat slabs.
7. Cost of concrete and steel in peripheral beams would be same in both cases, unless this beam is also prestressed.

As I do not have the actual costs as of now, I am not giving any typical cost comparison.  

regards

Dr. M. R. Kalgal
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prof.arc
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PostPosted: Fri Jan 02, 2009 12:16 am    Post subject: Cost implications between RC slab and Flat /PT slab Reply with quote

please add the warning - residential buildings are poorly supervised and joints may not be engineered properly at site. also they have plenty of brick walls that has to be borne by the slab !
ARC

On Thu, Jan 1, 2009 at 8:26 AM, drnsmani <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
           Dear Mr. Sampath,

I have designed only a few flat slab structures, made of RCC. They are for commercial buildings. Of course they are cheaper than beam-slab construction, due to the simplified form work. But I feel that they may not be useful for residential buildings, because the plan will not be uniform. PT slabs may be economical for large projects only, as we may have to pay for the PT contractors, separately.

Best wishes
Subramanian



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Sampath
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Joined: 30 Dec 2008
Posts: 71

PostPosted: Fri Jan 02, 2009 5:07 am    Post subject: Reply with quote

Dear All

Thanks for your replies.

It is now somewhat clear to me than earlier but it is apparent that the cost is dependant on several factors (for e.g. mimimum weight design of a steel structure may not give optimal disign as cost of connection is also important).

I would like to bring the attention of two more technogies which is not available in india I guess but we need to think about this also.

1. Bubble deck (voids in both direction)
2. Hollow core slab (I think this cannot be thought as flat slab construction as each slab unit has to be supported on two edges).

References:

1. Please google "Bubble deck"
2. http://www.bison.co.uk/products.aspx?ID=1

I have worked for a detailing solution to Bison and given a web link for their hollow core solution.

Attached two pictures.



HollowCore.jpg
 Description:
Hollow core e.g.
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HollowCore.jpg



BubbleDeck.jpg
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Bubble deck e.g.
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BubbleDeck.jpg


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ravee
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PostPosted: Fri Jan 02, 2009 8:51 am    Post subject: Cost implications between RC slab and Flat /PT slab Reply with quote

I do agree upon Dr Subramanian Sir, and Mr Chopda, I would like you to Just work out a simple Frame of 12.0mX12.0m considering a Basic rates available in the market for STEEL, CONCRETE, AND LABOUR. In other words a Comparative analysis B/w Conventional RCC System, Flat Plate, Flat Plate with DP’s  
And next with PT Flat Plate, PT Flat Plate with DP’s the Numbers Prove it

This type of Analysis Presentation is basically done here in Bangalore, and Proved upon

Regards
ravee Kumar

From: drnsmani [mailto:forum@sefindia.org]
Sent: Thursday, January 01, 2009 10:29 PM
To: econf@sefindia.org
Subject: [ECONF] Re: Cost implications between RC slab and Flat /PT slab



Dear Mr. Chopda,

In countries like USA, where labour costs are high, simplification of form work results in low labour costs and minimum construction time. When you consider the total cost you have to take into account many factors including cost of materials, cost of labour, cost of formwork, maintenance cost, etc. The cost of the particular system is also dependent on the selected span. For longer spans (say 25-30 feet) PT flat slabs will be more economical than any other slab system.

More deatails about the ecnomics of slab systems is given in the following paper:
Fintel, M., and Ghosh, S.K., Economics of Long span concrete slab systems for office buildings- A Survey, Concrete International, Feb. 83, pp.21-34

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





--- On Thu, 1/1/09, rbchopda wrote:    
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ravee
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PostPosted: Fri Jan 02, 2009 9:05 am    Post subject: Cost implications between RC slab and Flat /PT slab Reply with quote

Dear Sir
Can I have a copy of the mentioned Paper, I’ve been googling for quite some time to download.


From: drnsmani [mailto:forum@sefindia.org]
Sent: Thursday, January 01, 2009 10:29 PM
To: econf@sefindia.org
Subject: [ECONF] Re: Cost implications between RC slab and Flat /PT slab



Dear Mr. Chopda,

In countries like USA, where labour costs are high, simplification of form work results in low labour costs and minimum construction time. When you consider the total cost you have to take into account many factors including cost of materials, cost of labour, cost of formwork, maintenance cost, etc. The cost of the particular system is also dependent on the selected span. For longer spans (say 25-30 feet) PT flat slabs will be more economical than any other slab system.

More deatails about the ecnomics of slab systems is given in the following paper:
Fintel, M., and Ghosh, S.K., Economics of Long span concrete slab systems for office buildings- A Survey, Concrete International, Feb. 83, pp.21-34

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





--- On Thu, 1/1/09, rbchopda wrote:    
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Dr. N. Subramanian
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PostPosted: Mon Jan 05, 2009 3:39 am    Post subject: Re: Cost implications between RC slab and Flat /PT slab Reply with quote

Please send your email ID so that I may send it to you.
Best wishes  Very Happy
NS
[quote="ravee"]Dear Sir
Can I have a copy of the mentioned Paper, Iíve been googling for quite some time to download.
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