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Can we use Precast Floor Slabs?
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cvrm
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Joined: 16 Nov 2012
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Location: Chennai

PostPosted: Tue Nov 27, 2012 6:16 am    Post subject: Can we use Precast Floor Slabs? Reply with quote

Dear Colleagues:

There was a nice comment in the eC, that Tall Buildings should have stiff floor diaphragms and vertical walls. Of course, this expectation is valid even for low rise buildings. Experiments performed on isolated precast floor slabs with screed concrete showed that under statically applied in-plane lateral load, the precast slab system is extremely effective in transferring the loads with insignificant damage. This may have motivated some to propose use of precast floor slabs in Tall Buildings also. But, when the same experiments were repeated with vertical shaking also, the results were on the contrary. Even with small vertical shaking included, the performance deteriorates. Of course, post-earthquake performances indicated that it is difficult to ensure that precast floor slab always remain integral as one unit, especially under strong earthquake shaking.

Hence, if the intention is to have a Tall (and reliable) Building with integral action during strong earthquake shaking within the horizontal elements (e.g., floor slabs) and vertical elements (e.g., columns and structural walls), and between horizontal and vertical elements, it seems best to stay away from unreliable and vulnerable system, like precast floor slab systems.

with warm regards...
C. V. R. Murty
..

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suraj
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PostPosted: Tue Nov 27, 2012 11:49 am    Post subject: Tall Buildings & HCS provisions Reply with quote

Dear Eng
C. V. R. Murty
Tall Buildings & HCS provisions


  1. What I understand about HCS is that these are provided in combinations with RCC topping
  2. Cast  in situ beams & columns are provided as usual
  3. HCS are transported from factory & placed over beams in designed fashion
  4. Cast in panels are borne on full length between location of beams
  5. No screed is placed over panel deck
  6. A well designed thin RCC slab is placed over decking utilising decking as formwork
  7. Reinforcing bars are well arranged to tranform HCS panel dowels & cast in situ slabs into resulting required diaphragm action
  8. Such method is employed on fast track high rise construction

_________________
Thanks & Warm Regards
IntPE(India)Suraj Singh FIE Civil
Engineering & Arbitration

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Dr. N. Subramanian
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PostPosted: Tue Nov 27, 2012 8:22 pm    Post subject: Re: Tall Buildings & HCS provisions Reply with quote

Hi All,

I would like to appreciate Prof. Murty for his comments and info.

In this connection, the Special report published by Fintel in the Jan-Feb 1986 issue of PCI journal, on the performance of Precast and prestressed concrete in Mexico Earthquake will be useful:

http://fib.pci.org/pdf/publications/journal/1986/January-February/JL-86-JANUARY-FEBRUARY-2.pdf

Performance of Precast Concrete in February 22, 2011 Christchurch NZ Earthquake is available in:

https://pci.org/cms/cfcs/cmsIT/baseComponents/fileManagerProxy.cfc?method=GetFile&fileID=05AEE56C-9851-17DD-FE0E64CFDDCB159F

Another Reference at:
http://ir.canterbury.ac.nz/bitstream/10092/4395/1/12624116_ASCE%20congress_Peng%20et%20al_seismic%20performance%20and%20floor%20frame%20system.pdf

Best wishes,
NS

suraj wrote:
Dear Eng
C. V. R. Murty
Tall Buildings & HCS provisions

  1. What I understand about HCS is that these are provided in combinations with RCC topping
  2. Cast  in situ beams & columns are provided as usual
  3. HCS are transported from factory & placed over beams in designed fashion
  4. Cast in panels are borne on full length between location of beams
  5. No screed is placed over panel deck
  6. A well designed thin RCC slab is placed over decking utilising decking as formwork
  7. Reinforcing bars are well arranged to tranform HCS panel dowels & cast in situ slabs into resulting required diaphragm action
  8. Such method is employed on fast track high rise construction
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JayakumarK
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Joined: 16 Nov 2011
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PostPosted: Wed Nov 28, 2012 3:08 am    Post subject: Re: Can we use Precast Floor Slabs? Reply with quote

Hi everybody,

I was part of the design team which has designed a 70 storeys building in Dubai, and we have used precast HCS (hollow core slabs) with RCC topping. While preparing mathematical models (in ETABS / MIDAS), I have considered the total cross sectional area of the concrete (HCS+structural screed) to be effective for the in-plane/axial forces in the floor slab (modeled as one way slab), and only the topping thickness for the bending at the end supports.


Regards,
Jayakumar K
email: ejk.iitb@gmail.com


cvrm wrote:
Dear Colleagues:

There was a nice comment in the eC, that Tall Buildings should have stiff floor diaphragms and vertical walls. Of course, this expectation is valid even for low rise buildings. Experiments performed on isolated precast floor slabs with screed concrete showed that under statically applied in-plane lateral load, the precast slab system is extremely effective in transferring the loads with insignificant damage. This may have motivated some to propose use of precast floor slabs in Tall Buildings also. But, when the same experiments were repeated with vertical shaking also, the results were on the contrary. Even with small vertical shaking included, the performance deteriorates. Of course, post-earthquake performances indicated that it is difficult to ensure that precast floor slab always remain integral as one unit, especially under strong earthquake shaking.

Hence, if the intention is to have a Tall (and reliable) Building with integral action during strong earthquake shaking within the horizontal elements (e.g., floor slabs) and vertical elements (e.g., columns and structural walls), and between horizontal and vertical elements, it seems best to stay away from unreliable and vulnerable system, like precast floor slab systems.

with warm regards...
C. V. R. Murty
..

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cvrm
E-Conference Moderator


Joined: 16 Nov 2012
Posts: 12
Location: Chennai

PostPosted: Wed Nov 28, 2012 3:32 am    Post subject: Can we use Precast Floor Slabs? Reply with quote

Dear Mr. Suraj Singh

Thank you for bringing clarity to the matter by explaining the system in detail... This is an interesting system and it would be interesting to study the experimental behaviour of such composite slabs.

with warm regards...
C.V.R.Murty
..

________________________________________
Dear Eng
C. V. R. Murty
Tall Buildings & HCS provisions


What I understand about HCS is that these are provided in combinations with RCC topping
Cast in situ beams & columns are provided as usual
HCS are transported from factory & placed over beams in designed fashion
Cast in panels are borne on full length between location of beams
No screed is placed over panel deck
A well designed thin RCC slab is placed over decking utilising decking as formwork
Reinforcing bars are well arranged to tranform HCS panel dowels & cast in situ slabs into resulting required diaphragm action
Such method is employed on fast track high rise construction=

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cvrm
E-Conference Moderator


Joined: 16 Nov 2012
Posts: 12
Location: Chennai

PostPosted: Wed Nov 28, 2012 4:51 am    Post subject: Can we use Precast Floor Slabs? Reply with quote

Dear Dr. Sunramanian:

Thank you for the URLs; they are very useful. The one from NZ EQ gives a clean chit to (all) Precast Systems. Is this a common observation from all other earthquakes also? Or is it that NZs are making better precast structures?

with warm regards...
C.V.R.Murty
..

________________________________________
From: Murty C V R
Sent: Wednesday, November 28, 2012 9:02 AM
To: econf34289@sefindia.org
Subject: Re: Can we use Precast Floor Slabs?

Dear Mr. Suraj Singh

Thank you for bringing clarity to the matter by explaining the system in detail... This is an interesting system and it would be interesting to study the experimental behaviour of such composite slabs.

with warm regards...
C.V.R.Murty
..

________________________________________
Dear Eng
C. V. R. Murty
Tall Buildings & HCS provisions


What I understand about HCS is that these are provided in combinations with RCC topping
Cast in situ beams & columns are provided as usual
HCS are transported from factory & placed over beams in designed fashion
Cast in panels are borne on full length between location of beams
No screed is placed over panel deck
A well designed thin RCC slab is placed over decking utilising decking as formwork
Reinforcing bars are well arranged to tranform HCS panel dowels & cast in situ slabs into resulting required diaphragm action
Such method is employed on fast track high rise construction

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alpa_sheth
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...


Joined: 26 Jan 2003
Posts: 264

PostPosted: Wed Nov 28, 2012 8:28 am    Post subject: Can we use Precast Floor Slabs? Reply with quote

Dear All: 

As the current discussion is referring to New Zealand,  we should remember  that the precast industry has a stranglehold on the construction industry in NZ. Even after the earthquake, it is a foregone conclusion that a lot of precast will be used in the reconstruction because the industry has made all believe that only they would be able to deliver the reconstruction in the appointed time. Ofcourse as the country uses a lot of precast, it has  also seen a lot more research and development in the area.  


I quote from an EERI earthquake report on the NZ earthquake : http://www.eeri.org/site/images/eeri_newsletter/2011_pdf/EERI_NewZealand_EQRpt_web.pdf 
** With the exception of the precast stairs, the vast majority of (precast) elements and systems performed as intended. Emulative frames developed beam end plastic hinging to a level of damage commensurate with the seismic excitation; floor systems remained seated and intact, with damage limited in most cases to displacement compatibility cracks along the units, though cracking in the end regions of flange-hung double tees was observed and requires closer attention; and precast cladding panels generally remained attached, with only two exceptions noted. Precast stair elements collapsed in at least three multi-story buildings in the CBD (Figure 13), trapping occupants in the buildings for several
hours after the earthquake**



I would also draw attention to the foll paper during the annual technical conf of NZSEE on "Implementing lessons learnt"  earlier this year.  http://www.nzsee.org.nz/db/2012/Paper128.pdf   There is an imp concluding statement made in the paper "Seismic Performance of Reinforced Concrete Frames with Precast-Prestressed Flooring System" (Toniolo)  based on research done in Europe : 


**The calculations, performed to design the prototype of three storey structure with reference to the capacity of the testing plant in terms of applied forces and displacements, showed that the elastic dynamic modal analysis, based on the standard response spectrum, is not able to predict with sufficient accuracy the actual response of the structure. The map of forces and displacements can be much different. The elastic dynamic modal analysis remains a conventional approach of relatively simple application. Only the non linear dynamic analysis is able to predict with good accuracy the structural response to a given accelerogram. Non linear dynamic analysis could be for the future the approach for the verification of structures under seismic action, as suggested by the last fib Model Code.**



I am not sure how many structural designers are inclined to do this. I had mentioned in one of my mails that the  Chinese Code  does not allow Precast flooring systems for Higher seismic zones (equiv to IV and V) for buildings of any height and in lower seismic zones it disallows the same when h>50m. 


regards,


Alpa 






On Wed, Nov 28, 2012 at 12:51 PM, cvrm <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
           Dear Dr. Sunramanian:

Thank you for the URLs; they are very useful. The one from NZ EQ gives a clean chit to (all) Precast Systems. Is this a common observation from all other earthquakes also? Or is it that NZs are making better precast structures?

with warm regards...
C.V.R.Murty
..

________________________________________

From: Murty C V R
Sent: Wednesday, November 28, 2012 9:02 AM
To: econf34289@sefindia.org (econf34289@sefindia.org)
Subject: Re: Can we use Precast Floor Slabs?

Dear Mr. Suraj Singh

Thank you for bringing clarity to the matter by explaining the system in detail... This is an interesting system and it would be interesting to study the experimental behaviour of such composite slabs.

with warm regards...
C.V.R.Murty
..

________________________________________
Dear Eng
C. V. R. Murty
Tall Buildings & HCS provisions


What I understand about HCS is that these are provided in combinations with RCC topping
Cast in situ beams & columns are provided as usual
HCS are transported from factory & placed over beams in designed fashion
Cast in panels are borne on full length between location of beams
No screed is placed over panel deck
A well designed thin RCC slab is placed over decking utilising decking as formwork
Reinforcing bars are well arranged to tranform HCS panel dowels & cast in situ slabs into resulting required diaphragm action
Such method is employed on fast track high rise construction
     




     



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manieck2010
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Joined: 06 Jul 2010
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PostPosted: Wed Nov 28, 2012 9:44 am    Post subject: Can we use Precast Floor Slabs? Reply with quote

Dear All,


Yes we can use precast prestressed hollow core slab for highrise building with proper topping as per diaphragm design. But we have careful at some points which are described in NZS researches. Some them as follows

1, positive moment failure
2. Negative moment failure
3. Bearing failure
4. Differential deflection with edge element(beams)
We are implementing HCS up to 19 story building. It reduce building weight. For long spans more than 6 to 7 m, we can use solid prestressed slab also in high seismic zone. 


-BR
Manish Khandelwal
Structural Design Engineer
Vahanen(India)
Mobile +91-89 6882 5695
Email-manish.khandelwal@vahanen.com (Email-manish.khandelwal@vahanen.com)
Website-www.vahanen.com

On Tue, Nov 27, 2012 at 5:19 PM, suraj <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
           Dear Eng
C. V. R. Murty
Tall Buildings & HCS provisions


  1. What I understand about HCS is that these are provided in combinations with RCC topping
  2. Cast in situ beams & columns are provided as usual
  3. HCS are transported from factory & placed over beams in designed fashion
  4. Cast in panels are borne on full length between location of beams
  5. No screed is placed over panel deck
  6. A well designed thin RCC slab is placed over decking utilising decking as formwork
  7. Reinforcing bars are well arranged to tranform HCS panel dowels & cast in situ slabs into resulting required diaphragm action
  8. Such method is employed on fast track high rise construction

     


Thanks & Warm Regards
Int P Eng (India)
Suraj Singh(Faridabad NCR)
Contracts Consultant +919810610718
IntPE(I)800042-9
Discipline: Civil Engineering
Valid Up to: 30/09/2015

     



     


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Dr. N. Subramanian
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PostPosted: Wed Nov 28, 2012 10:03 pm    Post subject: Re: Can we use Precast Floor Slabs? Reply with quote

Dear Prof. Murty,

You may find more info. in the following:
[1] Seismic Design of the International Federation for Structural Concrete (fib), “State-of- the-Art Report on The Seismic Design of Precast Concrete Building Structures,” Draft Report of Task Group 7.3 of Commission 7,.
[2] Fintel, M., “Performance of Buildings With Shear Walls in Earthquakes of the Last Thirty Years,” PCI Journal, Vol. 40, No. 3, 1995, pp. 62-80.
Another report which may be of interest you:
An Evaluation of Seismic Design Guidelines
Proposed for Precast Concrete Hybrid Frame Systems[http://srg.cce.iastate.edu/Final%20reports/PCMAC%20Hybrid%20Frame%20Validation%20-%20FINAL%20REPORT.pdf]

You made my name bright by missplling it and including "Sun" in it Smile!

Regards,
NS
cvrm wrote:
Dear Dr. Sunramanian:

Thank you for the URLs; they are very useful. The one from NZ EQ gives a clean chit to (all) Precast Systems. Is this a common observation from all other earthquakes also? Or is it that NZs are making better precast structures?

with warm regards...
C.V.R.Murty
..

________________________________________
From: Murty C V R
Sent: Wednesday, November 28, 2012 9:02 AM
To: econf34289@sefindia.org
Subject: Re: Can we use Precast Floor Slabs?

Dear Mr. Suraj Singh

Thank you for bringing clarity to the matter by explaining the system in detail... This is an interesting system and it would be interesting to study the experimental behaviour of such composite slabs.

with warm regards...
C.V.R.Murty
..

________________________________________
Dear Eng
C. V. R. Murty
Tall Buildings & HCS provisions


What I understand about HCS is that these are provided in combinations with RCC topping
Cast in situ beams & columns are provided as usual
HCS are transported from factory & placed over beams in designed fashion
Cast in panels are borne on full length between location of beams
No screed is placed over panel deck
A well designed thin RCC slab is placed over decking utilising decking as formwork
Reinforcing bars are well arranged to tranform HCS panel dowels & cast in situ slabs into resulting required diaphragm action
Such method is employed on fast track high rise construction

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swamikrishnan
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Joined: 28 Jul 2011
Posts: 18

PostPosted: Thu Nov 29, 2012 12:51 am    Post subject: Re: Can we use Precast Floor Slabs? Reply with quote

I am not sure I am interpreting Er. Jayakumar's statement correctly.  Nevertheless, I would use the contribution of ONLY the topping slab when computing floor diaphragm shear capacity;  I would NOT include the precast plank thickness in this calculation since the planks (which come in small sizes) are not capable of  transferring shear forces (the panels can slip past each other).  This is similar to straight sheathing in wood floors (diagonal sheathing is considered to be a flexible diaphragm, whereas straight sheathing is usually not trusted to provide any diaphragm action).

Chapter 22 of FEMA-547 talks about  diaphragm rehabilitation techniques and warns of the lack of diaphragm action in "poorly connected precast floors" in the very first paragraph (Section 22.1):

http://www.google.com/url?sa=t&rct=j&q=straight%20wood%20sheathing%20diaphragm&source=web&cd=2&ved=0CDUQFjAB&url=http%3A%2F%2Fwww.fema.gov%2Flibrary%2Ffile%3Ftype%3DpublishedFile%26file%3Dfema547part3.pdf%26fileid%3D4b979b10-1a8d-11dc-b1f0-000bdba87d5b&ei=ObC2UJ7FL4KGjAKttYDgBw&usg=AFQjCNHBr8nrqs2GwBaryEFmMOD91x6JaA&cad=rja

Swaminathan Krishnan
California Institute of Technology
http://krishnan.caltech.edu

JayakumarK wrote:
Hi everybody,

I was part of the design team which has designed a 70 storeys building in Dubai, and we have used precast HCS (hollow core slabs) with RCC topping. While preparing mathematical models (in ETABS / MIDAS), I have considered the total cross sectional area of the concrete (HCS+structural screed) to be effective for the in-plane/axial forces in the floor slab (modeled as one way slab), and only the topping thickness for the bending at the end supports.


Regards,
Jayakumar K
email: ejk.iitb@gmail.com


cvrm wrote:
Dear Colleagues:

..

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