A hard to find tool, but works very well is a handheld diamond cutter with a flush cutting asembly and steel cutting disks.
We have used to cut really thick shafts with this equipment, and the finnish is better than melting and blow away.
the steel cuttind disks look almost exactly the same as a traditional diamond disk, but it uses different cutting segments.

I could have been a retrofit to shore up a sagging house. I have seen that in many houses.

use a plasma cutter if you can get ahold of one not as hot as a torch

do you have to cut it to remove it or just cut it. I would just have a fire watch and cut it with a torch