www.sefindia.org

[subha_mukherjee]

Sometimes the RCC beam design fail in shear due to torsion acting on the RCC beam. Some consultant advice to minimise the torsion by applying reduction factor. Other consultant advice not to do that, even if that factor is applied detailing of beam has to be done in proper manner. My question is how can i detail such a beam?
                                              Regards,
                                                          Subhajit M

[vikram.jeet]

Torsion effect :-

Carrying Load through associated torsion is costly,, but it is to be seen wether torsion is equilibrium torsion Or Compatibility Torsion.
In case it is Equilibrium Torsion - I. e a cantilever beam emerging out from main beam at some point in span of main beam without any stabilizing span at back of cantilever beam,, THEN TORSION NEEDS TO BE CONSIDERED in main beam.

But if it is Compatibility torsion emerging as result of frame analysis ,, either it is to be catered for in design  OR MX  be released in input model so that effects of released torsion are taken care in   enhanced BMs in output of computer.

Also compatibility torsion exist at junction of Main beam and secondary beam,, Either it be taken in design Or Mx in main beam  be released in Input model ,, causing enhanced BM in Sec beam.

However For purists if structure designs - wanting to design as per natural structure behaviour without any release of Mx in beams for compatibility torsion -- IT IS ADVISED TO MODEL THE STRUCTURE FRAMES ALONG WITH SLABS  , to get actual results.  By virtue of this the torsion on beams will be greatly reduced  - - I think. BARE FRAMES WITHOUT SLABS IN any model will have two effects :-
Higher support moments,, especially at end beams supports
Higher Torsion moments  

Detailing :-
Even if Compatibility torsion is released in main beam,,  little torsion cracking can be taken care by ignoring Tc bd relief in beam while finalising stirrups,  and providing side face reinf bars. A personal opinion subject to rejection.

Also kindly refer IS 456 on Torsion where a note regarding Torsional cracking is given as being controlled by minimum shear reinf.