Floor joist support

Hi, Helping a friend remodel their old farm house purchased recently. the second floor has 2 bathrooms with plumbing drains running perpendicular to the joist. So the creative hack cut a U out of 5 joists to accommodate the 4" cast drains! Worse than that it is near the center of the room which spans 16'. Temporarily, we put jack stands under the area, removed the bathroom drains and tubs. We plan on sistering some 2x10's for support.
How long on either side should I run the boards?
Adhesive?
Screws or bolts?
Would plywood strips work better than 2x10's?
Other ideas?


Thanks

 

You can sister the joists, but if I had five cut I would just replace the whold joist end to end. A splice is never as strong as a new one. If that is not possible, I would use the longest ones I could get in, create a "slight" bow and bolt together. A metal plate(16 ga.) between would even be better.