Can you reduce its dimensions increasing lateral deformation of the building?
by doing that you also distribute horizontal forces a litle more to the remaining collumns...
I like STRAP very much... Unfortunatly I can't say I know STAAD... I know some others - SAP2000, Robot Millenium, etc... STRAP is better than those...
Here in Europe STAAD doesn't sell much
Either you have a lot of mass on restrained d.o.f. or the first modes are torsion ones (torsion modes have no participation factor)...
if none of this I dont know... :(