There is currently no efficient way to consider the live load reduction factor in STAAD.Pro. It would be fantastic to add a parameter to the design section (e.g., under CSA S16-19 or AISC 360-16) to consider a live load reduction on an element by element basis. This would be manually calculated by the analyst until someone at Bentley can figure out how to determine tributary area for an element based perhaps on the floor load command (easy example for columns, TA = axial load/input floor live load; for girders, TA = [shear 1 + shear 2] / input floor live load).
Thank you for posting this idea. There is however already a posting on this already, SP-I-276 To customize formula or coefficient for Live Load reduction . We have added this to the backlog . Can you add your comments onto that idea so we have them all collated and this thread will be closed as a duplicate idea.