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Beam Strip Raft Foundation

 
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jeeb
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Joined: 23 Dec 2018
Posts: 10

PostPosted: Fri May 15, 2020 4:49 pm    Post subject: Beam Strip Raft Foundation Reply with quote

Hi, could seniors provide some insight on the beam-strip raft foundation as shown. It consists of ground bearing beams (supporting columns point loads and walls) and ground bearing slab which are designed separately. The ground bearing slab is only reinforced with a top mesh reinforcement. I would like to ask:
1.     How to design the beams?
2.     Should bottom reinforcement be provided in the ground bearing slab?



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es_jayakumar
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Joined: 24 Nov 2011
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Location: Cochin

PostPosted: Sun May 17, 2020 6:19 am    Post subject: Reply with quote

I hope this is a slab-beam type raft foundation. Why is it founded at ground level ? If the centre of gravity of the loads and that of the raft coincides, the upward soil pressure will be uniform. In that case, the slab and beams can be designed similar to a framed structure, using provisions of IS-456. It is a practice to provide steel at top and bottom in raft slabs. You can refer "Design of Reinforced Concerete Foundations" by PC Varghese, for guidance. Books by Swami Saran & Nainan P Kurian also cover this topic in detail.

E S Jayakumar
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jeeb
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PostPosted: Sun May 17, 2020 2:01 pm    Post subject: Reply with quote

Dear Jayakumar,  Thank you for your reply. In fact I've this situation as show. I need to avoid footings encroaching the existing building and drain. So I thought of proving this solution while searching existing literature for potential solutions. What would you suggest as foundation solution for this problem?


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es_jayakumar
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PostPosted: Sun May 17, 2020 2:19 pm    Post subject: Reply with quote

Slab-beam type raft looks fine for your case. As the raft will experience hogging moment at beam supports, top reinforcement alone will not suffice for raft slab.

E S Jayakumar
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jeeb
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PostPosted: Mon May 18, 2020 2:48 pm    Post subject: Reply with quote

Dear Jayakumar, thank you very much.
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