Ok, now I see what you did (I think). You put a 6x12 (which is larger
than the beam in question) in your beam program and placed an arbitrary
load of 200 plf on it. You then let it come up with steel beams that had
simlar deflections and were not overstressed.

The problems with this approach are as follows:

1) This will give conservative stiffness results (not necessarily bad)

2) This *may* give you a steel beam that is overstressed as your 200 plf
load may be less than the actual service load. You would have been
better off using the correct section ( three 2x12's ) and a load that
was at the limit stress for this section.


Regards,


--
Rob Munach, PE
Excel Engineering
PO Box 1264
Carrboro, NC 27510