What is this metal rail in my basement and can I hang my 80 lbs punching bag on it? Thank you.
This is a load-bearing I-beam. This beam is holding up your house, so as long as it's well secured, you should be able to add an extra 80 lbs to it. They make mounting brackets specifically for hanging heavy bags onto these: http://amzn.to/2iXojjG
Your beam ends in the middle of the room, being supported by a post. This is weird and atypical. I am afraid only the person who implemented this solution could speak of it's purpose and strength.
Usually, I-beams like this are the toughest part of the house, however in your setup it's mounting looks super-flimsy. I am afraid that the punching bag is the worst possible thing to hang from it (ok, second-worst. A swing would be worse). When you apply full force of your body to the bag horizontally and perpendicularly to the beam, you may knock the beam off the post that's supporting it.
If the other side is also supported by a post, this is pretty much bound to happen sooner or later with horizontal loads. I'd treat this setup as for strictly vertical loading only.
If I saw it in a garage, I'd say it's a form of immobile gantry crane for hoisting a car engine up and down, while the car under it handles the side motion. Or maybe someone installed something very heavy on the floor upstairs and this was implemented to prevent the floor from buckling - which would work only short-term, as the posts would sink, eventually, because the floor isn't very strong in the middle of a room.
It looks like you have two things going on with this
- You have a large opening in your basement. If you look to the left side of your first photo, you can see what looks like framing for a doorway. That framing is picking up the load of the floor joists above it. But your I-beam is probably spanning a much larger opening (maybe 15 to 20 feet). That I-beam is picking up the load of this longer opening. Whomever did this was smart enough to realize they needed something more substantial than lumber to support a gap like that(you'd be amazed at the contractors who would throw a couple of 2x4s in there and call it good, only to have it sag down the road)
- I don't see how the I-beam is secured to... anything. It's sitting on the joists but I don't see anything holding it there except the weight of the floor, and the 1x4 running parallel. Normally I would expect to see bolts holding it somewhere, but I see none. You might want to bring in an engineer and have him look at this to see if it's safe to hold your house up, let alone hang a bag.
If I were you, I'd put a hook on the 2x8 joists for now. They won't go anywhere.
One other safety note: it looks like they used metal sheeting to make an air duct out of your joists. But that first picture shows a wire running between the joist and the metal sheet. That's a potential shock/fire hazard. I'd have that fixed if I were you.