Hello dears, 

I used recently STAAD Pro for analyzing a steel plate, anyway as we know the result of Von mises stress to be compared with Fy of the steel plate,

 Von mises stress = 0.707 sqrt((smax-smin)^2+smax^2+smin^2) the result given is less than Fy of the plate then its ok and passed

but i calculate this value from the principal stresses

manually its okay and safe with the plate 

but from the software result its different in fact 

the value here from the software is over than the limit !!!!!

can Bentley provide a justification ?