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circular slab

 
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shivani soman
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Joined: 29 May 2018
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PostPosted: Tue Nov 26, 2019 6:58 am    Post subject: circular slab Reply with quote

hello sefi members,
In designing a circular slab with columns and beams as shown in the attachment can we design the middle rectangular portion of slab as rectangular slab or do we need to consider the overall shape and design it as circular slab.



COLUMN LAYOUT-Model.jpg
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circular slab column layout
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COLUMN LAYOUT-Model.jpg


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es_jayakumar
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Joined: 24 Nov 2011
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Location: Cochin

PostPosted: Tue Nov 26, 2019 8:43 am    Post subject: Reply with quote

You can design the slab panel in question as a rectangular one with the edge conditions of "Interior panel". No need to associate it with the properties of a circular slab.

E S Jayakumar
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shivani soman
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PostPosted: Tue Nov 26, 2019 9:25 am    Post subject: Reply with quote

THANK YOU
es_jayakumar FOR HELPING
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venkatasalamkl
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Joined: 27 Oct 2017
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PostPosted: Tue Nov 26, 2019 12:50 pm    Post subject: Reply with quote

Hi Shivani,

If you are planning to use coefficient method in IS 456 for your (interior panel) slab design, I would recommend you to read the assumptions behind the derivation of that table.

Below is the few assumptions behind the derivation of coefficients given in IS 456

1. Coefficient method is applicable only when support (Support line) is rigid and unyielding.

2. I understand that its very hard to make some element as a highly rigid element. For these cases Canadian literature (Also Can be found in Reinforced concrete design by P.C Varghese) gives some inputs.
a) To use coefficient method your beam depth should be atleast 2.5 times your slab depth. This is ratio is only applicable for square slab.
b) You have some empirical equation to determine the beam width as well which you can get in textbooks.

Please have a look into all these clauses before using the coefficients given in IS 456.

If you are using coefficient method directly without knowing the assumptions behind then I would say that your slab is under designed.

Above all the better way (From my understanding) to design slabs is to go with any finite element software available in the market. Even in software you should very careful while you are modeling and choosing analysis methods,... ( There are good manuals, modeling guides from CSI,..which are available online and you can download it for free of cost).

In addition to the points above I would request you to have a look into the assumptions behind design aids you that you are using for your projects. Understanding those assumptions will give you a  very different perspective of how you see a problem.

Thanks and Regards,
Venkat
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es_jayakumar
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PostPosted: Tue Nov 26, 2019 2:12 pm    Post subject: Reply with quote

I agree with Mr.Venkat. The accurate method would be to model the bottom slab along with the side wall and beams in a software. This will take care of the BM transferred to the edges of bottom slab, from the side walls when the tank is filled with water. We can approximate the tank to octagonal shape also, if required, for the easiness in modeling the bottom slab.

E S Jayakumar
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