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Table 19 on shear strength of RCC

 
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amandeep verma
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PostPosted: Wed Nov 20, 2019 6:31 am    Post subject: Table 19 on shear strength of RCC Reply with quote

Dear Sefians,

Please comment is there no change in shear strength of RCC beam if we use higher grade of steel as main bar?

Table 19 depends only upon % age of tension reinforcement not on grade of steel.

Why should we use higher grades of steel then ?
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Dr. N. Subramanian
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PostPosted: Thu Nov 21, 2019 12:50 am    Post subject: Re: Table 19 on shear strength of RCC Reply with quote

Dear Er Verma
The beam has to be designed for flexure also!

Not only the Indian code but other codes also do not consider fy of steel in shear strength calculation of beams.

Also note that in earthquake resistant design only shear stirrups of grade 415 steel is permitted. ( need to check new version of IS 13920, whether higher grade is permitted now)


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Subramanian

amandeep verma wrote:
Dear Sefians,

Please comment is there no change in shear strength of RCC beam if we use higher grade of steel as main bar?

Table 19 depends only upon % age of tension reinforcement not on grade of steel.

Why should we use higher grades of steel then ?
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es_jayakumar
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PostPosted: Sat Nov 23, 2019 4:53 pm    Post subject: Reply with quote

The values given in Table 9 have been computed using the formula (Rangan B V) given at 39.2.1 of SP.24 (Explanatory Handbook). It is made clear in the clause that the formula is a semi-empirical one.
The book “Reinforced Concrete Design to Eurocodes” By Prab Bhatt at al says:
An accurate analysis for shear strength is not possible. The problem has been solved by testing beams of the type normally used in practice. Shear strength depends on several factors such as the percentage of flexural steel in the member. This affects the shear capacity by restraining the width of the cracks and thus enhancing the shear carried by the aggregate interlock along the cracks. It also naturally increases the shear capacity due to dowel action and increase the depth of the section in compression.
Dr.H.J.Shah, in his book “Reinforced Concrete” Vol-I says :
(i)     When amount of tension steel increases, the depth of neutral axis increases and thus, the depth of un-cracked concrete increases. This increases the capacity of section in shear
(ii)      When amount of tension steel increases, the cracks formed are smaller which improves the aggregate interlock. Also because of larger steel area, the dowel action is improved. This further improves the capacity of section in shear.

From the foregoing, it can be surmised that it is the quantum of the steel, not its grade that has telling influence on the shear capacity of concrete, since the formula used is a semi-empirical one, perhaps proposed based on experimental data.

E S Jayakumar
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