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Doubt on End Extension of Rebars (12 times dia or d)

 
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vineetha_palankar
SEFI Member
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Joined: 29 Aug 2011
Posts: 3

PostPosted: Sun Jan 22, 2023 7:10 pm    Post subject: Doubt on End Extension of Rebars (12 times dia or d) Reply with quote

Hello All,

I Have a doubt regarding the End extension of rebars. SP34 states that it must be max of 12 times diameter or d as shown in figure below .

I have 2 cases in which I am finding difficulty to incorporate this clause ,

1.If a beam is 650mm deep for a span of 5000mm , and if I am using 12 dia rebars then (12*12= 144, d = 614mm & Ld of 12 dia for M30 = 552mm). The extension of bars beyond the theoretical cut-off point shall be 614mm =d , but I feel Ld is sufficient.

2.Similarly for Raft Foundations where d is say 2000mm, in such cases the extension of rebars can be Ld instead of d, as Ld is max 1472mm for 32 dia rebar but providing d instead of Ld seems unreasonable.

Request all to share your opinion and Guide me If am wrong.



Regards,
Vineetha
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vikram.jeet
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Joined: 26 Jan 2003
Posts: 3660

PostPosted: Mon Jan 23, 2023 4:55 pm    Post subject: Reply with quote

As per IS 456 ,, location at which a rebar is not required,, the reinf shall be extended either 12d Or  deff,,
Hence this must be adhered.

Earlier version of IS 456 ,, before 1978 ,, only 12d extension was there,, but d extension was added in 1978 version,, since theoretical cutoff pt as worked out needs safety envelop. This has to be adhered without any if or but.

Only at simply supported members ,, the extension of + ve moment rebar into support must be Ld/3.
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