[SEFI] waffle slab & grid slab
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thensenamar mp
Aug 17, 2008, 4:44:41 AM8/17/08
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hi,
what is grid slab & waffle slab.
let me know any book's which have give details for designing of the same.
regards
thensenamar m.p.
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what is grid slab & waffle slab.
let me know any book's which have give details for designing of the same.
regards
thensenamar m.p.
Did you know? You can CHAT without downloading messenger. Go to http://in.webmessenger.yahoo.com/
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dnnagaraj
Aug 17, 2008, 7:16:15 AM8/17/08
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Dear Friend,
It is a system of slabs and beams, where the slab is supported by a network of cris-cross beams, interwoven in a particular patterns. It is indentified many terms / names like, Ribbed slabs,Hollow blocks slabs, Grid slabs, waffle slabs, coffered slabs, haurdy slabs etc.
There are many types of grid slabs based on the pattern of the beams arrengement.
1) Square Grid
2) Rectangular Grid
3) Polygonal Grid
4) Dia-grid etc.
The analysis is done based on the deflection of the central grid and taking into consideration the inter-grid torsion as given in "Theory of Elasticity" by Thimoshenko and Goddier. There are manuals / handbooks brought by CSIR, which adopts
integro-differential method to arrive at the BM, SF and Torsion.
For enhanced info please refer to any standard books on Design of Concrete strcutures.
A few books to name are
1.Advanced Concrete structures by Prof. Krishnaraju,
2.Design of Concrete strcutures by H.J.Shah
3.Theory of Elasticity by Thimoshenko and Goddier.
Regard,
D.N.Nagaraj
--- On Sun, 8/17/08, thensenamar mp wrote:
It is a system of slabs and beams, where the slab is supported by a network of cris-cross beams, interwoven in a particular patterns. It is indentified many terms / names like, Ribbed slabs,Hollow blocks slabs, Grid slabs, waffle slabs, coffered slabs, haurdy slabs etc.
There are many types of grid slabs based on the pattern of the beams arrengement.
1) Square Grid
2) Rectangular Grid
3) Polygonal Grid
4) Dia-grid etc.
The analysis is done based on the deflection of the central grid and taking into consideration the inter-grid torsion as given in "Theory of Elasticity" by Thimoshenko and Goddier. There are manuals / handbooks brought by CSIR, which adopts
integro-differential method to arrive at the BM, SF and Torsion.
For enhanced info please refer to any standard books on Design of Concrete strcutures.
A few books to name are
1.Advanced Concrete structures by Prof. Krishnaraju,
2.Design of Concrete strcutures by H.J.Shah
3.Theory of Elasticity by Thimoshenko and Goddier.
Regard,
D.N.Nagaraj
--- On Sun, 8/17/08, thensenamar mp wrote:
| Quote: |
| From: thensenamar mp Subject: [SEFI] waffle slab & grid slab To: gen...@sefindia.org Date: Sunday, August 17, 2008, 2:14 PM |
http://www.sefindia.org/forum/viewtopic.php?p=8125#8125
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jatfuentes
Aug 17, 2008, 8:05:45 AM8/17/08
to gen...@sefindia.org
Dear thensenamar,
A good book to check is “Reinforced Concrete Design “ by Chu-Kia Wang and Charles Salmon.
Basically is grid of T beams were the flange of the “T” is the slab. This is done in order to save concrete.
Regards,
jatfuentes
A good book to check is “Reinforced Concrete Design “ by Chu-Kia Wang and Charles Salmon.
Basically is grid of T beams were the flange of the “T” is the slab. This is done in order to save concrete.
Regards,
jatfuentes
http://www.sefindia.org/forum/viewtopic.php?p=8126#8126
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drnsmani
Aug 17, 2008, 10:18:49 AM8/17/08
to gen...@sefindia.org
Hi Thensenamar,
You may also look into Design and construction of concrete shell roofs, G. S. Ramaswamy. Revised edition, 1984. 758 pp.
(Late) Prof. GSR was the director of SERC and was responsible for developing SERC and there are several interesting structures at SERC, Chennai housing their Lab., including waffle slab.
Best wishes
Subramanian
--- On Sun, 8/17/08, jatfuentes wrote:
You may also look into Design and construction of concrete shell roofs, G. S. Ramaswamy. Revised edition, 1984. 758 pp.
(Late) Prof. GSR was the director of SERC and was responsible for developing SERC and there are several interesting structures at SERC, Chennai housing their Lab., including waffle slab.
Best wishes
Subramanian
--- On Sun, 8/17/08, jatfuentes wrote:
| Quote: |
| From: jatfuentes Subject: [SEFI] Re: waffle slab & grid slab To: gen...@sefindia.org Date: Sunday, August 17, 2008, 5:35 PM |
Dear thensenamar, A good book to check is “Reinforced Concrete Design “ by Chu-Kia Wang and Charles Salmon. Basically is grid of T beams were the flange of the “T” is the slab. This is done in order to save concrete. Regards, jatfuentes De: thensenamar mp [mailto:fo...@sefindia.org] Enviada em: domingo, 17 de agosto de 2008 05:45 Para: gen...@sefindia.org (gen...@sefindia.org) Assunto: [SEFI] waffle slab & grid slab |
http://www.sefindia.org/forum/viewtopic.php?p=8129#8129
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vikram.jeet
Aug 18, 2008, 1:52:31 AM8/18/08
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Waffle Slabs-- in accrdance with 30.1( b) of IS 456
Precast waffle units forming the bottom profile of the waffle
system are kept in position side by side which also serve as permanent
shuttering for the system. Reinforcement is placed in these
precast waffles for ribs formed between two waffles.Topping slab
50-75mm as per design requirements with central mesh of 6 to 8mm dia
can be provided.
Precast waffles are 25 mm thick folded plate with 4mm reiforcement
and lifting hooks at top(hooks also facilitate binding with topping reinf),
these are flat at centre and slant at sides with depth of slant generally
375mm(or different) so as to make overall depth of rib
as 375mm+ topping thickness
Waffles when palced side by side, provide ribs with top width 150-175mm and
bottom width 100-120mm excluding precast thickness
The design of waffles can be done as slab/ Flat slab
(if within limits of Cl 30.5 of IS 456, which generally these satisfy)
i)In case alround beams of depth preferabbly same as waffle depth
run(for aesthetic reasons), then it can be designed as a slab supported on four sides
and coefficients of IS 456 can be used for working out renf in ribs
as per spacing of ribs which is generally 900mc/c in both directions
-- can also be desined as one way if supported with beams on two opposit sides
-- at bottom one bar is possible whereas at top of 2 bars can be provided.
-- stirrup is 2- legged with triangular shape
---there is be a continuous groove at bottom( being joint in two precast waffles)
-- Precast waffle units can be cast at site from plastic moulds
ii) Can also be designed as flat slab system with waffles around columns
solid to have check on two way shear
best regards
vikramjeet
Precast waffle units forming the bottom profile of the waffle
system are kept in position side by side which also serve as permanent
shuttering for the system. Reinforcement is placed in these
precast waffles for ribs formed between two waffles.Topping slab
50-75mm as per design requirements with central mesh of 6 to 8mm dia
can be provided.
Precast waffles are 25 mm thick folded plate with 4mm reiforcement
and lifting hooks at top(hooks also facilitate binding with topping reinf),
these are flat at centre and slant at sides with depth of slant generally
375mm(or different) so as to make overall depth of rib
as 375mm+ topping thickness
Waffles when palced side by side, provide ribs with top width 150-175mm and
bottom width 100-120mm excluding precast thickness
The design of waffles can be done as slab/ Flat slab
(if within limits of Cl 30.5 of IS 456, which generally these satisfy)
i)In case alround beams of depth preferabbly same as waffle depth
run(for aesthetic reasons), then it can be designed as a slab supported on four sides
and coefficients of IS 456 can be used for working out renf in ribs
as per spacing of ribs which is generally 900mc/c in both directions
-- can also be desined as one way if supported with beams on two opposit sides
-- at bottom one bar is possible whereas at top of 2 bars can be provided.
-- stirrup is 2- legged with triangular shape
---there is be a continuous groove at bottom( being joint in two precast waffles)
-- Precast waffle units can be cast at site from plastic moulds
ii) Can also be designed as flat slab system with waffles around columns
solid to have check on two way shear
best regards
vikramjeet
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ibarua
Aug 20, 2008, 3:50:42 AM8/20/08
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20th Aug 2008
Grid & Waffle slab: Krishna Raju's book, 'Advanced Reinforced Concrete Design' contains an explanation and an exapmple of grid slab design. Such slabs are often cast-in-situ, but precast waffles with in-situ joints have been useed, though I would not recommend pre-cast units in seismic sensitive zones. I have used cast-in-situ grid slabs extensively in some of the buildings my firm has designed - one spanned 12*18 m.
Indrajit Barua.
On Sun, 17 Aug 2008 thensenamar mp wrote :
Grid & Waffle slab: Krishna Raju's book, 'Advanced Reinforced Concrete Design' contains an explanation and an exapmple of grid slab design. Such slabs are often cast-in-situ, but precast waffles with in-situ joints have been useed, though I would not recommend pre-cast units in seismic sensitive zones. I have used cast-in-situ grid slabs extensively in some of the buildings my firm has designed - one spanned 12*18 m.
Indrajit Barua.
On Sun, 17 Aug 2008 thensenamar mp wrote :
| Quote: |
http://www.sefindia.org/forum/viewtopic.php?p=8143#8143
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jlakhlani
Aug 20, 2008, 7:31:30 AM8/20/08
to gen...@sefindia.org
Dear Sefians,
As suggested by Mr. Barua, N. Krishnaraju's book explains grid slab in a very lucid manner. Basic principal to be kept in view is, the grid slab behaves in a manner identical to a two-way slab. The ribs are provided to increase moment of inertia of the section.
In a two-way slab, corner steel is required to cater for the torsional moments. Same way, in a grid slab, when the same is modelled as a grid of rib beams and analysed, heavy torsion is found in the beams in corner portions of the grid slab. Care should be taken to consider torsional rigidity of the beams in the analysis. (Many a times in a building space frame, torsional moments are released as they are usually of small magnitude. In a grid slab, torsional moments should not be released)
Details for a 20 m x 20 m grid slab designed by us is available on the link,
http://www.lakhlani.com/sabhagruh.php
Regards.
Jayant Lakhlani
For
Lakhlani Associates
www.lakhlani.com
--- On Wed, 20/8/08, ibarua wrote:
As suggested by Mr. Barua, N. Krishnaraju's book explains grid slab in a very lucid manner. Basic principal to be kept in view is, the grid slab behaves in a manner identical to a two-way slab. The ribs are provided to increase moment of inertia of the section.
In a two-way slab, corner steel is required to cater for the torsional moments. Same way, in a grid slab, when the same is modelled as a grid of rib beams and analysed, heavy torsion is found in the beams in corner portions of the grid slab. Care should be taken to consider torsional rigidity of the beams in the analysis. (Many a times in a building space frame, torsional moments are released as they are usually of small magnitude. In a grid slab, torsional moments should not be released)
Details for a 20 m x 20 m grid slab designed by us is available on the link,
http://www.lakhlani.com/sabhagruh.php
Regards.
Jayant Lakhlani
For
Lakhlani Associates
www.lakhlani.com
--- On Wed, 20/8/08, ibarua wrote:
| Quote: |
| From: ibarua |
|
Subject: [SEFI] Re: waffle slab & grid slab To: gen...@sefindia.org |
| Date: Wednesday, 20 August, 2008, 7:50 AM |
20th Aug 2008 Grid & Waffle slab: Krishna Raju's book, 'Advanced Reinforced Concrete Design' contains an explanation and an exapmple of grid slab design. Such slabs are often cast-in-situ, but precast waffles with in-situ joints have been useed, though I would not recommend pre-cast units in seismic sensitive zones. I have used cast-in-situ grid slabs extensively in some of the buildings my firm has designed - one spanned 12*18 m. Indrajit Barua. |
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pathre_v
Aug 20, 2008, 11:07:27 AM8/20/08
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Grid slabs can be designed like two way slab by factors as per IS 456. I am a structural designer in Gulf and here it is a common practice to design grid slab with 150 mm x 300mm grid beams @ 800 mm crs. for large spans up to 7m x 7m .
regards
Vijay
regards
Vijay
--- On Wed, 20/8/08, ibarua wrote:
[quote]From: ibarua
Date: Wednesday, 20 August, 2008, 1:20 PM
20th Aug 2008
Grid & Waffle slab: Krishna Raju's book, 'Advanced Reinforced Concrete Design' contains an explanation and an exapmple of grid slab design. Such slabs are often cast-in-situ, but precast waffles with in-situ joints have been useed, though I would not recommend pre-cast units in seismic sensitive zones. I have used cast-in-situ grid slabs extensively in some of the buildings my firm has designed - one spanned 12*18 m.
Indrajit Barua.
On Sun, 17 Aug 2008 thensenamar mp wrote :
[b]--auto removed--
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