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Can we use Precast Floor Slabs?
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alpa_sheth
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PostPosted: Thu Nov 29, 2012 10:09 am    Post subject: Shear wall behaviour in Tall Buildings during earthquakes Reply with quote

Dear Dr Subramanian,

I have started a new thread but am responding to your  mail in the precast thread re. shear wall behaviour.

Thanks for the references. I think they  are  perhaps  dated, esp with regard to shear wall behaviour. Our understanding of shear wall behaviour has undergone a sea change in past 5-10 years. The spurt of earthquakes  has given us a lot of new insight into their performance- especially  the 2010 Chile earthquake and the 2011 Japan and NZ earthquakes

Of particular concern has been the compression buckling of walls seen in these earthquakes, much of it due to lack of boundary element confinement (large spacing of hoop steel)

pl see the foll paper:
http://www.jaee.gr.jp/event/seminar2012/eqsympo/pdf/papers/176.pdf

best regards,

Alpa Sheth


[quote="Dr. N. Subramanian"]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]
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SanjeevKrSharma
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PostPosted: Thu Nov 29, 2012 4:24 pm    Post subject: Reply with quote

Dear All
I agree with the comment of Mr Swaminathan and as a practice only the reinforced structural topping typically varying from 60mm to 100mm is considered to transfer the diaphragm forces in seismic areas.  
Though some guide lines for design of diaphragms exist in PCI handbook, Precast Concrete Institute (US) has initiated a research project DSDM (Diaphragm Seismic Design Methodology) where a full scale shake table was done and some reports are published on the observations. A list of these can be found at url below
http://nees.org/resources/4420/download/List_of_DSDM_Publications.doc
In Europe in low seismic areas, however there is a practice not to do any structural topping over hollowcore slabs, but instead make shear keys at the edges of hollowcore, reinforce them and grout them with a specially designed low shrinkage mix.
As a remark on comparing hollowcore with the formwork in one of the earlier threads, I would like to add that hollowcore slab does not act as formwork alone but is very effective in transferring gravity loads and along with structural topping it acts as a composite slab. It is pretensioned hollowslab typically made with M40 to M60 greater grade of concrete with special mix having low water cement ratio. Middleast and Europe has seen large scale application of these slabs in multistory buildings, villas, shopping malls, large span carparks etc. We also see many references of their use in Australia and Newzeland.
Mr Murthy gave a very valid observation on HCS behavior in vertical accelerations as there might be stress reversal and disintegration in case they are not well connected into to the topping that can bind or hold them together in such cases. It might be possible to use the shear key formed at the edges to integrate HCS with topping in case of vertical accelerations though tests may be required to substantiate.
Finally, I also think that since these are primarily one way behaving slabs with no reinforcement (only strands) in precast part, a very careful detailing is required to mitigate effects of deformation incompatibility that may arise with adjacent beams, shear walls, columns etc. in highrise buildings and in high seismic zones.

Warm Regards
Sanjeev K Sharma
Principal Consultant
Melior Structural Solutions
www.meliorstructural.com
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Dr. N. Subramanian
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PostPosted: Thu Nov 29, 2012 9:08 pm    Post subject: Re: Can we use Precast Floor Slabs? Reply with quote

Dear Prof. Murty,

PCI Journal-Winter 2012 has the following reconnaissance reports of Chile, NZ and Japan EQs

Preview of PCI's New Zealand earthquake reconnaissance team report by Robert B. Fleischman, José I. Restrepo, Joseph R. Maffei, and Kim Seeber
http://www.pci.org/view_file.cfm?file=JL-12-WINTER-9.pdf

Preview of PCI's Japan Earthquake Reconnaissance Team Report By
Richard Sause, Robert Frosch, S. K. Ghosh, Jason Lien, Clay Naito, Larbi Sennour, and Toshi Yamanishi
http://www.pci.org/view_file.cfm?file=JL-12-WINTER-10.pdf

Observations from the February 27, 2010, earthquake in Chile By
S. K. Ghosh and Ned Cleland
http://www.pci.org/view_file.cfm?file=JL-12-WINTER-11.pdf

I have not gone through them- but hope will provide latest info. on behavior of diff. structures in latest EQs

The Link provided by Er Alpa is good and deals with shear wall behaviour in EQs.

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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Dr. N. Subramanian
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PostPosted: Thu Nov 29, 2012 10:44 pm    Post subject: Re: Shear wall behaviour in Tall Buildings during earthquake Reply with quote

Dear Er Alpa,

Thanks for the link of the paper authored by Profs. Wallace and Jack  Moehle, who are the leading researchers in USA and have published a number of papers in this area. This particular paper synthesizes the concepts in shear walls.

As you have rightly noted, the behaviour of barbell-shaped walls,Low-rise wall, slender walls, perforated walls, and coupled walls are different and have to be designed and detailed properly. Barbell walls have boundary columns  which improve wall stability as the boundary columns have additional longitudinal reinforcement for moment resistance. In addition they help to anchor beams framing into the wall.

Flanged walls like T, L, C, and I configurations and Core walls may provide better safety.

Like columns, the axial force level and slenderness have to be considered carefully in the design, as the vertical bars may buckle in slender walls, as shown in the recent EQs.

Coupled wall in which cantilever walls are connected by coupling beams may be a bit difficult to construct, as the coupling beam with diagonal reinforcement may pose constructability. The Recent issue of Concrete International (Nov. 2012) contains the description of a building in SFO which has post tensioned shear walls (which will make the wall back to the vertical after the seismic event) as well as innovative composite coupling beam.

In the following document  Prof. Wallace provides a designers guide to Displacement-Based Design of RC Structural Walls

http://www.seas.ucla.edu/~wallace/Files%20-%20Teaching%20Page/CE%20243A/ho%20DBD%20wall.pdf

In USA, the 'shear' walls are referred correctly as structural walls as the name shear wall is a misnomer!

Regards,
Subramanian

[quote="alpa_sheth"]Dear Dr Subramanian,

I have started a new thread but am responding to your  mail in the precast thread re. shear wall behaviour.

Thanks for the references. I think they  are  perhaps  dated, esp with regard to shear wall behaviour. Our understanding of shear wall behaviour has undergone a sea change in past 5-10 years. The spurt of earthquakes  has given us a lot of new insight into their performance- especially  the 2010 Chile earthquake and the 2011 Japan and NZ earthquakes

Of particular concern has been the compression buckling of walls seen in these earthquakes, much of it due to lack of boundary element confinement (large spacing of hoop steel)

pl see the foll paper:
http://www.jaee.gr.jp/event/seminar2012/eqsympo/pdf/papers/176.pdf

best regards,

Alpa Sheth


Dr. N. Subramanian wrote:
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]
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prof.arc
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PostPosted: Fri Nov 30, 2012 12:08 am    Post subject: Can we use Precast Floor Slabs? Reply with quote

Dear Co-ordinators [Dr. CVRM & Dr. Alpa Sheth],

I note with interest the flood of emails on this e-conf
The effort of SEFI can be fruitful only if the outcome results in a NEW BIS Code
on TALL BUILDINGS

Based on the e-conference, I hope you could organise a group of
research persons working under you to prepare
a draft code and send it to CED-39 for consideration

best wishes
sincerely
ARC

On 11/27/12, cvrm <forum@sefindia.org> wrote:
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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Dr. N. Subramanian
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PostPosted: Fri Nov 30, 2012 6:01 am    Post subject: Re: Can we use Precast Floor Slabs? Reply with quote

Dear Prof. ARC,

I also feel that SEFI should take action to prepareva code on Tall Buildings.
The committee should consist of researchers as well as practioners, and a few contractors also!

Regards,
NS
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Engineer
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Posts: 10

PostPosted: Fri Nov 30, 2012 8:42 am    Post subject: Tall Building Article Search on Google Reply with quote

Simple Google search for the string “tall building” will give 2.24 Million pages on the web. One can narrow down this search by providing clue to the Google.
Clue means telling Google to search within particular site/domain/country/company/university etc.
The Google Option to find the “tall building” string within domain/website are following
· Searching within American Universities – site:edu
·  Searching within British Universities – site:ac.in
· Searching within IIT Bombay site – site:iitb.ac.in
· Search within Indian Companies – site:in
· Search within SEFI website site:sefindia.org
The string “tall building” can be found inside any of the following file types
· Microsoft Word file ( Clue for Google – filetype:doc )
· Microsoft Excel File ( Clue for Google – filetype:xls )
· Microsoft Power Point Presentation file ( Clue for Google – filetype:ppt )
· Acrobat PDF file ( Clue for Google – filetype:pdf )
· Post Script file ( filetype:ps)Examples of Using Google Smart (Advance) Search:
If one wants to find the string “tall building” within the website of Council on Tall Buildings & Urban Habitat (www.ctbuh.org), Use following information in Search box to be type
"tall building" site:ctbuh.org


Similarly to find the string “Tall building” inside  IIT Bombay website
"tall building" site:iitb.ac.inSearching Particular File format:
One can find only Power Point Presentation file containing the string “Tall Building” through Universities in America, using following input in Search Box
"tall building" site:edu filetype:ppt

Google can help to find only PDF files containing the complete phrase “tall building” inside Universities in UK using following information inside search box
"tall building" site:ac.uk filetype:pdf


Searching the string “Tall Building” within Acrobat PDF files on American University websites
"tall building" site:edu filetype:pdf

Use of Both filetype and site clue will make google search quick and effective


Hemant Gor, GorHemant@GMail.com
https://twitter.com/structurejob

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