getting slight bend out of massive plate

[sv_i]

Originally Posted by PLAYA

i think its got a slight curve cos he buys the sheets in 6m lengths on 2.4 wide, then picks them up with a fork in the middle.

It might also be slightly curved from when your sheet was cut from the stock sheet - if they used a mechanised oxy machine to cut your piece off, then that would put a slight curve in it, or if it was stored in a stack with one end sticking out, that can also bow steel plate.

If it is 250 grade steel then it won't have much flex to it, if it is 350 grade it should have a little bit of flex to it and it may be easier just to bolt/clamp/weld it in position to your RHS supports.

Honestly, I'd leave it as is, just put lots of heavy weight in the middle (with the bend up) for a while, see how it goes, it may actually straighten after a while.