They would have had heavy machines on that floor so I'm not too surprised. The heavy stuff is all set on concrete in more modern machine shops but not as much back then. I've seen old belt drive machine shops that were built on bridge timbers.
The Piquette Avenue plant had assembly on the second floor so you know that they had to be pretty stout buildings. Here is some good photos from the museum in modern day.
https://www.tflcar.com/2018/05/ford-...-avenue-plant/
and another:
https://journal.classiccars.com/2018/09/22/the-building-of-legend-fords-
piquette-avenue-plant/
One more from You-Tube:
https://www.youtube.com/watch?v=qcmGApho3u4