Clarification on allowable stress of Staad output Result?

Hi,

i designing Cold form section as per IS801-1975, Since the section is not available in the section database , i incorporate the section properties in the Section database, and i designed the framing, here, my members are failing due to the 6.3 LTB where  Allowable stress on unbraced bending along major axis is 18.998 Mpa, but hand calculation of the allowable stress should around 136.6 Mpa, I need know that on what basis the BendUnbraced 6.3 LTB Allowble stress is calculated by Staad, Kindly Let me know.