EN 1993-1-1:2005 has provisions to reduce the moment resistance of the cross section when certain conditions for shear capacity are not met as mentioned in Cl:6.2.8. The Dutch National annex also specifies for:

• Class 1 and Class 2 I-section with equal flanges for bending about weak, the design value of the yield moment reduced by shear will be determined using:
  $M_{z,V,\mathrm{Rd}}=\frac{q_y\times W_{\mathrm{Pl},z}\times f_y}{{\gamma }_{\mathrm{M0}}}$
  where

  $q_y$	=	$1.03\sqrt{1-{\left(\frac{V_{y,\mathrm{Ed}}}{V_{\mathrm{pl},y,\mathrm{Rd}}}\right)}^2}$
  $W_{\mathrm{Pl},z}$	=	the plastic section modulus of the member about the Z axis
  $f_y$	=	yield strength
  $V_{y,\mathrm{Ed}}$	=	shear force applied in the Y direction
  $V_{\mathrm{pl},y,\mathrm{Rd}}$	=	shear capacity in the Y direction. STAAD.Pro calculates this per Eqn. 6.18 in EN 1993-1-1 as described in the National Annex using $A_v=2b\times t_f$.
  ${\gamma }_{\mathrm{M0}}$	=	safety factor

• Class 1 and Class 2 square and rectangular hollow sections when bending about strong axis, the design yield moment reduced by shear force may be determined using:
  $M_{Y,V,\mathrm{Rd}}=\frac{M_{\mathrm{pl},Y,\mathrm{Rd}}-[(1-q_z)\frac{1}{2}t\times h^2\times f_y]}{{\gamma }_{\mathrm{M0}}}$
  where

  $q_z$	=	$1.03\sqrt{1-{\left(\frac{V_{z,\mathrm{Ed}}}{V_{\mathrm{pl},z,\mathrm{Rd}}}\right)}^2}$
  $M_{\mathrm{pl},Y,\mathrm{Rd}}$	=	the plastic moment capacity about the Y axis
  t	=	thickness of the member
  h	=	depth of the member
  $V_{z,\mathrm{Ed}}$	=	shear force applied in the Z direction
  $V_{\mathrm{pl},z,\mathrm{Rd}}$	=	shear capacity in the Z direction. STAAD.Pro calculates this per Eqn. 6.18 in EN 1993-1-1 as described in the National Annex using $A_v=\frac{h}{b+h}A$

• For class 1 and 2 square and rectangular hollow section when bending about weak axis, the design yield moment reduced by shear force may be determined using:
  $M_{z,V,\mathrm{Rd}}=\frac{M_{\mathrm{pl},z,\mathrm{Rd}}-[(1-q_y)\frac{1}{2}t\times b^2\times f_y]}{{\gamma }_{\mathrm{M0}}}$
  where

  $M_{\mathrm{pl},Z,\mathrm{Rd}}$	=	the plastic moment capacity about the Z axis
  b	=	width of the member
  $V_{\mathrm{pl},y,\mathrm{Rd}}$	=	shear capacity in the Z direction. STAAD.Pro calculates this per Eqn. 6.18 in EN 1993-1-1 as described in the National Annex using $A_v=\frac{b}{b+h}A$