The floor is also reciprocal but in a different way. Still, every joist rests on his fellow.

First there was a bit of prep work to do. I had to fix one of the floor boards that had come away, and also add a central tyre to support the middle of the floor. Technically the central support wasn’t needed as the floor would be supported only from the base plate on the edge tyres, but an extra support never hurt anyone:

I was very fortunate to get a lot of I beams very cheap online. I filled the gaps between them using broken up pallets.

Some joints

Side view

Top view