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Raft foundation design
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abhishek_prajapati
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Joined: 26 Jul 2011
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PostPosted: Sat May 21, 2022 7:31 am    Post subject: Local Thickening of Raft Reply with quote

Dear Members,

Following are the features of Raft, as per design:-
RAFT DIM - 58M x 33M.
Thickness - 800MM, satisfying displacement & SBC criteria.

Local Thickening required because :-
1. The flexure Reinforcement demand for design Strip is very high approx. 12000mm2/m (Although it's peak).
2. Shear Value for Strip it is showing failure.
The dimension of this local thk Raft would be 22M x 12M.
3. We think, increasing overall depth of raft would be uneconomical.

following are the queries:-

If we need to increase the depth of raft locally,

1. what should be appropriate:-

a. increase thickness above base Raft.(pic attached)
b. increase thickness below base Raft.
2.  Structural & Construction wise, which option is  better?

3. Please provide reinforcement detailing for both the options, it would be of gr8 help.


Kindly guide.



Loacal Thickning of Raft.png
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vikram.jeet
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Joined: 26 Jan 2003
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PostPosted: Sat May 21, 2022 8:32 am    Post subject: Reply with quote

Advantages &  disadvantages of two options :
Thickening at top :
Excavation easy since one level
Extra excavation to accommodate top thickening - if basement exist otherwise no extra
But there will be additional cost of sand filling at top to achieve basement floor level in caSe of basement , otherwise if no basement - no such expenditure.

Bottom thickening :
EXCAVATION to be precise to accomodate thickenings.

Both options are in practice
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vikram.jeet
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PostPosted: Sat May 21, 2022 9:07 am    Post subject: Reply with quote

Just to add
Reinforcement detailing will be easy for top thickening .Since bottom bars require continuity and bottom mesh reinf bars are of larger dia than top bars.

For bottom thickening , bars need to be bent to shape .
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spsvasan
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Joined: 18 Dec 2008
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PostPosted: Sun May 22, 2022 2:58 am    Post subject: Reply with quote

If membrane water proofing is being planned, it will be better to have the bottom surface in one level

S.P.Srinivasan
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