So, is it an existing beam? Has there been a pillar in the middle, or has it always been undersized?
It would probably take quite a lot for you to make such a reinforcement good, but if you can do the work yourself, it might be worth a try. Otherwise, you can replace the glued laminated beam with a steel beam that can bear with a lower profile.
In any case. For your steel to be of any use, it should be placed on the underside. That is, the surface that becomes convex under load. Maybe that's what you meant, but it's just as well to clarify. The steel also needs to be tensioned to be of any use. A piece of coarse threaded rod welded at one end might work. The best attachment is to place a shoe that embraces the end of the beam and is bolted/screwed on top and underneath.
