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Crack width calculation- ε2 is calculated to be more ε1

 
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kawshik9
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PostPosted: Wed Apr 27, 2022 7:29 am    Post subject: Crack width calculation- ε2 is calculated to be more ε1 Reply with quote

Dear all,

I am designing water conveying underground Box and I have following query regarding crack width calculation.

" Strain due to stiffening effect of concrete between cracks ε2 is calculated to be more ε1, leading to negative value of Avg strain εm. What does it mean? should we consider it to be uncracked or neglect ε2 and calculate crack width with εm = ε1".

Please clarify my doubt. Thanking you

Kawshik
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vikram.jeet
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PostPosted: Thu Apr 28, 2022 11:50 am    Post subject: Reply with quote

Just a thought on this issue :

Pl check that SI units being used for all inputs of formula

Verify the tensile stress in conc at tension face , for M25 , if stress donot exceed , then section is deemed to be uncracked. Permitted stress for uncracked condition is  1.3 Mpa  for direct tension and 1.8  Mpa for bending tension . For combined tendion and bending pl see unity check.
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kawshik9
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PostPosted: Thu Apr 28, 2022 1:09 pm    Post subject: Reply with quote

Dear sir,

I have checked tensile stress in concrete for uncracked section and it is only  0.34 MPa which is less than Permitted stress. Thankyou for suggestion.

I have checked the issue in RC Design by Pillai & Menon text book. There it is mentioned if εm <0, the section is uncracked.


Thankyou once again.



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vikram.jeet
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PostPosted: Fri Apr 29, 2022 4:06 am    Post subject: Reply with quote

As per spirit of  IS 3370 p2 , if tensile  stresses are within permissible limits , crack control is achieved automatically. This is as per WSM .
In case LSM is followed , there is need to check crack width .

A stress of 3.4 kg/cm2 as against 12 kg/cm2 / 18 kg/cm2 is well within and hence rest assured yr section is uncracked as per IS stipulations.
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