Quanski:
That used to be a fairly common form of concrete construction for floors and roofs. One way systems were just conc. joists formed with pans, framing into major conc. beams on column lines. Two way systems actually used square or rectangular pans, with joists running in both directions. And, the design process used essentially std. concrete design methods for whatever time period. Who are the major suppliers you contacted? I can’t imagine that there is no info. available for design and layout for construction. I’ll bet you can still rent the pans. And, on those kinds of buildings I’m surprised you can’t find any construction documents, unless they are really old construction. You certainly need a lot more info. to start to attack your problem than provided in your OP, not the least of which might be; conc. strength, reinforcing strength, quantities, lengths, locations, etc., layout dimensions, joist width and depth, slab thickness, on and on. CRSI always had good coverage of this conc. construction method.