what do i replace these beams with (floorboards on strip footings)

ok as the picture shows
http://i139.photobucket.com/albums/q...01/bearers.jpg
i have ripped all the floorboards up in the hallway. My intention is to lay yellowtongue constructafloor back down and then a floating floor over the top.
But before i lay the yellowtongue back down, i figure that the floor wont be at this stage ever again in my life time so i should probably do something about the slight bow in these beams.
Is there anything that is recommended to either:
a) take the bow out of the center by using some sort of packing compound in the centre of the beams
b)replace with another appropriate replacement beam in their place.

the span is approx 1700mm but at the 3 beams you can see at the back (just in front of the pink bathroom) spans about 1850mm
the centres are approx 450mm (but if i am replacing them then i can make that what ever i want i guess)
the beams sit on packing aterial each side and also on a strip of wood that runs the length of the concrete footings.
the beams themselves are approx 100x45mm


Read the full thread at RenovateForum.com...