Are you talking about SIB floors?
My Achilles flooring pieces were 2 sheets of aluminum, probably around 1/8" thick, sandwiching a piece of plywood. The edges were extruded shapes, a sort of off-center U on the sides, and a tongue and groove thing on the front and back edges. The molding pieces were glued on, I think (no rivets or screws or welding, that I can recall.)
The stiffener pieces sat in some riveted-on channels at the outside, right under the tubes.
A friend fabbed a floor for a 16' Bombard SIB out of a single piece of sheet aluminum that bolted to the keel pieces. He retained the original wood front pieces. Much stiffer than the original ones, but a pain in the butt to re-assemble.
Hope this helps.