I stand (actually sit) in astonishment; great looking job.
I get 167 cu ft or 10500# (5+ tons-american); adding the steel frame ,base, and some rock/gravel and some safety factor , I think 7.5 tons is a fair design basis for total weight. Some evaluation of the concrete floor is worth while.
Or , with four legs ,maybe a one ft circle or square of 1/4" steel for feet. would give about 2 ton/sqft on the floor. Since the floor is inteded for living space it may have had some quality control. I once had concrete basement floor in Chicago area that actually had a 1" hole in it. I suspect it was poured in the winter and the concrete was poured over some chunks of ice ( there was nothing under the hole for about 6"( the basement was not intended as regular living space). Do they ever pour concrete in the winter where you live?
I would like to know if you own the weld shop or won a lottery.