changing the angle of roof beams

huangyhg

changing the angle of roof beams
i'm working on designing a barrel roof, and i am using staad pro to do so. when i have my girders vertical i need bigger beams then i do if i rotate my girders to the slope of the roof, i was expecting the opposite to be true, any insight on why this might be
can you elaborate more?
regards,
lutfi
if you mean the principal axis orientation, i would expect the minor axis parallel to roof slope to be more efficient only if wind is the critical load.