If you refer to the AISC-360-10 design, in section no H1.3, it has been mentioned that, for a doubly symmetric rolled compact member with KLz < KLy subject to combined axial force and bending only about the major axis, it is permissible to consider the two independent limit states, In-plane stability and Out of plane stability separately as in H1.3 in lieu of the combined approach outlined in section H1.1 .

 The equation H1-2 is suggested for the limit state of out of plane buckling and LTB.

 The equation H1-2 is an optional equation which can provide a more economical solution in some cases.

However, as this approach is optional. The designer is given with his choice to opt for using any of these equations when the necessary conditions are satisfied or he may compare both the eqns (H1-1 and H1-2) and select the highest ratio or the lowest ratio.

 

For the very same reason, INT parameter has been added in Staad which gives user 4 separate options by which he can use his engineering discretion to design the doubly symmetric compact  rolled section.

 

INT  0 - Checks both H1.1 and H1.3 and reports the lower ratio as critical

  This parameter allows designer to choose the highest ratio after checking both the equations and this will ensure the most conservative design.

INT  1 - Check both H1.1 and H1.3 and reports the higher ratio as critical

         As the highest of both the ratios is selected, so this parameter ensures  the most optimum design.

INT  2 - Always checks per H1.1 even when H1.3 may be applicable

         This will check H1.1 even when the condition demanded in the chapter H1.3 is also met.

 

INT  3 - Checks H1.3 in lieu of H1.1 when applicable

         This will check H1.3 instead of H1.1 when the condition demanded in the chapter H1.3 is also met.