Beams in torsion

Beams can develop torsion as a result of the analysis model or due to out of balance down-stand nib loads.

Torsional loads from the analysis model can either be designed for or, in certain conditions, ignored if omitted from the analysis. Thus if you have a structure that requires torsional resistance for stability (cantilever perpendicular from another beam) then you must design for torsion. However in a basic ground beam arrangement you can ignore the torsion if you omit it from the analysis. 

Grillage with torsion. Note moments at ends of beam runs that develop torsion in the perpendicular member, particularly at corners.	Grillage with torsion released in MasterFrame.

To release all the members torsionally in MasterFrame without all the effort of pinning members individually, in the MasterFrame editor go to the 'Analysis > Global Analysis Options > Ignore Torsional Stiffness' menu and tick the box.

Where torsion does exist it is checked in accordance with BS8110 Pt 2 Clause 2.4 or EC2-1-1 Clauses 6.3 and 9.2.3. Only the main rectangular cross-section is considered. 

Any area of main steel and Asv/Sv required to resist torsion is then deducted when designing your normal bending and shear.

It should be noted that clause 2.4.5 states that (v + vt)< vtu. If this check fails then adding more main or shear reinforcement will have no effect.  v, vt & vtu are all based on the un-reinforced section. Increase your Fcu or section size. Make it squarer.