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[diwakark]

Hi All,Currently, we are referring the guidelines of CSAA23.3:19 (Canadian code for RCC design) for designing a metro station. In Cl.11.3.9, code suggest considering additional longitudinal reinforcement due to presenceof shear force (Eq. 11.14) in beams & slabs. But it also highlights that ifmember is not subjected to significant torsion & significant tensionforces, this requirement can be satisfied by extending the flexural tensionreinforcement by distance dv cot θ. Here, code has not provided the exact definition/value ofsignificant tension & significant torsion?Can anyone please elaborate it further, where we have to provide additionallongitudinal reinforcement due to shear and where only dv cot θ extension issufficient?

[vikram.jeet]

Two types of torsions emerge from structural arrangements,,
1) Compatibility Torsion
A secondary beam supported by main beam/s,,
Here since there is partial fixity at ends,, the edge moments of partial fixity from sec beam get transfered to main beam as torsion *. This is Compatibility torsion, if secondary beam is designed as simply supported,,  this torsion is generally taken care while detailing of main beam. As per IS 456 , minimum shear reinf is suffice to take care of such torsionsl cracking.

2) Equilibrium Torsion  :- But if sec beam ends are taken fully monolithic,, the torsion created in main beam needs to be treated as equilibrium torsion and main beam needs to be designed with torsion reinf. Also a cantilever beam emerging
from Mainbeam will transfer entire cantilever moment to main beam as Equilibrium torsion and there is no option to avoid this torsion.

Additional reinf in form of longitudinsl bars on tension reinf plus longitudinal bars of skin reinf  plus additional stirrups reqd if Equilibrium torsion exist.

Compatibility torsion :- tackled in Detailing
(Just personal view)
Stirrups :- shear reinf worked out without considering Tcbd reilef
Skin reinf :- provide 0.1 percent of x sec area

Some views are personal and can be ignored

[vikram.jeet]

* Torsion on main beam due to fixity moment from sec beam

This can be worked out by distributing end moment from main beam based on flexural stiffness of sec beam and torsional stiffness of main beam parts on either side of sec beam junction.

However in software, readily available

[vikram.jeet]

But if u are working as per Canadian codes,, need to follow country code,

Generally I reiterate :

ANALYSIS IS UNIVERSAL
DESIGN IS NATIONAL
DETAILING IS PERSONAL
&
MODELLING HAS TO BE IDEAL