Plate buckling effects due to direct stresses at the ultimate limit state

SOFiSTiK
1

As per Eurocode 1993-1-5 $4: Plate buckling effects due to direct stresses at the ultimate limit state,
In calculating longitudinal stresses, account should be taken of the combined effect of

  1. shear lag and
  2. plate buckling.

I know I can use non-effective width to account for the shear lag effect, but what about plate buckling?

2

AQB does it itself
look in examples for class 4 sections