Peter, I can tell you that a bouncing basket ball or forklift will definitely make solid resonating sound, but at the same time you will have a secure feeling. Although if some one were to drop a ton or more of re-bar all at once, that will leave you heading toward the door. Don't ask how I know. This is very different than wood squeaking and saging, hollow sounds you will get routinly with wood floors. With speed floor allow 12" for floor thickness at a minimum.

It was #5500 pounds Eldon and it only fell 2 feet or so. I didn't feel scared

Well Scott, Ok it was a bit higher and a bit heavier than I mentioned. But contrary to what many will say. I tend to be a bit conservative.