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Slab Reinforcement Details

 
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ramu_se
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PostPosted: Fri Jul 03, 2020 11:52 pm    Post subject: Slab Reinforcement Details Reply with quote

Hi All,

I have designed a two way slab of 3.73mX4.42m with the condition of two adjacent edges discontinuous and got the following reinforcement details.

Mx(+ve) - T8@300mm c/c

Mx(-ve) - T8@190mm c/c

My(+ve) - T8@300mm c/c

My(-ve) - T8@300mm c/c

How to details this reinforcements?? Since i have got the Mx(-ve ) reinforcement more

Please guide me.

Ramu.
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ramu_se
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PostPosted: Sat Jul 04, 2020 11:49 pm    Post subject: Reply with quote

The Mx(-ve) reinforcement should be provided in top.

Is it fine to provide less reinforcement in bottom and more reinforcement in top.
Please guide me.
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sakumar79
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Joined: 18 Apr 2008
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PostPosted: Sun Jul 05, 2020 4:22 am    Post subject: Reply with quote

Dear Er Ramu,
    In two way slabs, especially when designed using IS code (coefficients table for two way slab), when you have a continuity, the top reinforcement will be more than the bottom reinforcement.

   There are two ways in which slabs are detailed - either using cranked rods or by using separate bars. Both have their advantages and their disadvantages. If you use cranked rods method, you will be providing T8@190 both at bottom and at top. If you use separate bars, you can provide T8@300 at bottom and T8@190 at top. You can also think alternatively to provide T8@300 at bottom and T8@150 at top OR T8@300 at bottom and T10@300 at top so that detailing at site will be easier and checking also will be easier.

   It appears that you are a fresh graduate or a student. You should work first under an experienced consultant before commencing independent practise. These are very basic practical questions that should be covered by interaction with seniors at office. Each office will have their own style of design and detailing.

Hope that helps
S Arunkumar
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es_jayakumar
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Joined: 24 Nov 2011
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Location: Cochin

PostPosted: Sun Jul 05, 2020 7:58 am    Post subject: Reply with quote

SP-34 (Detailing Handbook) has, in Fig.9.5, given the methods of detailing slab reinforcements, that are lucid. Now-a-days, cranking of bars in the slabs is mostly avoided and discontinuous straight bars are provided, instead. This helps us to provide different spacing for top and bottom bars. At a continuous edge, the top steel to be provided shall be the maximum of that required for the slab in question and the adjacent slab. That way, your T8@190mm c/c can be of lesser spacing, if the steel requirement for the negative moment in the adjacent span is more. It is better not to average the negative  BMs on either side of the support and find a common area of steel. Provide steel based on the maximum of the two BMs.

E S Jayakumar
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ramu_se
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PostPosted: Fri Jul 10, 2020 12:34 am    Post subject: Reply with quote

Thank you sir.

Please guide for deflection check in two way slab.

Is it fine to check span to depth ratio which satisfies IS-456 2000 cl.23.2.1
for deflection?

Thanks,
Ramu.
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es_jayakumar
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PostPosted: Fri Jul 10, 2020 1:30 am    Post subject: Reply with quote

Yes, Er.Ramu...
you familiarise yourself with the deflection check theory and examples given in any good text book. You can check the calculation by using the attached simple Spreadsheet prepared by me. Try to acquire more theoretical and practical knowledge in structural engineering.
Best wishes....

E S Jayakumar



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DESIGN OF SLABS FOR FLEXURE AND DEFLECTION.xls
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