Torsional equivalent area (Bredt)

Hi all, I hope you are doing well.

I want to ask about the calculation of the torsional equivalent area of a reinforced concrete pier with an oval cross section. I have defined the cross in sofiplus cross section editor with a perimeter reinforcement which is fully active to torsion. Could you please provide me with information if the calculation of the Bredt’s area is correct? I have also attached a screenshot from the result viewer.

Thank you for your time


The Bredt area will be generated by joining the activated torsion reinforcements to form a polygon. If the number of reinforcement rods increases, such discrepancies can occur as there is an upper limit to the considered corner points. The best way is to set all reinforcement passive in torsion and define an additional separate reinforcement as the single reinforcement layer available in torsion, then define multiple single rod reinforcements (for example 8 or 10 rods) to cover the oval form of the cross section with a polygon, for example, a hexagon, decagon.

This is okay because, at the end of the day, Ak will only be calculated for the longitudinal shear of the torsion, and only its value is important.