It's a large, thick I-Beam that runs along the roof in my garage. That's my garage door opener motor by the way...
It runs the entire length of my house all along the basement ceiling...pretty much exactly center in my house.
If it matters, the house was built in 1949 and is a 2 story plus basement.
The bag, I would have to guess is at least 80 pounds...obviously due to the awkwardness of it, it's hard to tell, it could very well be 100 pounds. The only reason I'm reluctant to call it 100 for sure is because it doesn't seem as tall as some of the ones I see in pics, which I believe are "full-size" or 100-pounders.