One of the differences in the last version of the code ISO+19902-2020 to check the allowable stresses was the implementation of a reduction factor that modifies the yield strength, due to the effect of Axial tension, compression, bending, shear, and torsion. this reduction it's specified in chapter 13.3.4

The effect of torsion on the strength of tubular members subjected to axial tension or compression or bending can be ignored if, using the definitions of

where τt is the torsional shear stress due to forces from factored actions 

If Formula (13.3-9) is not satisfied, calculate a reduced value of representative yield strength, fy,t, using

when the relationship between torsional shear stress and 0.2fv/rRv don't meet, the value for the  yield strength getting with the formulation 13.3-10 shall be into Formulae (13.2-1), (13.2-8) and (13.2-9), and Formulae (13.2-13) to (13.2-15) to determine corresponding reduced representative values of tensile strength ft,t, local buckling strength fyc,t, and bending strength fb,t, respectively. The effect of torsion on shear strength is accounted for by Formula (13.2-20).

Below you can find a quick verification for the internal process for the calculate allowable stresses in sacs using Code ISO - 19902-2020

communities.bentley.com/.../Allowable-Stress-issue_2D00_Verification.xlsx