Drilling, cutting, lots of ways to remove material .... figuring out the "best" for a given situation is the harder part.
If they are threaded steel rods embedded in a concrete floor, then would cutting them off flush to the floor be an acceptable option? If so (depending on rod size) a simple oscillating multi-tool (or even a hacksaw) might be the simplest approach.
If it's something else, then pictures would definitely be helpful for providing other options.