What size joists?
What size pipe?
A piece of angle iron across the top won't do it: you need to reinforce above and below (the top's in compression, the bottom's in tension, and both are completely necessary.
Maybe a set of them, above and below... depends on the size of pipe vs size of joist. Personally, I'd want an engineer to spec that sort of solution. A few hundred bucks, but I sleep better at night.
Other, more straightforward options:
- make the new connection lower, so that the pipe runs under the joists. Depends on what's downstairs.
- reframe that section of the floor, the way you would for a staircase or skylight opening, with a doubled header at each end.
- my favourite: change the design, so as to avoid the problem in the first place.