Abstract: An improved steel and concrete floor system in which a corrugated steel deck is supported on shelves fixed to the sides of parallel spaced joists. Each joist has a top chord forming a shear connector to cause composite action to occur between the joist and a slab poured on the deck, in which the topchord is embedded. The deck acts as a form for pouring the slab, and is a permanent part of the composite floor system. The deck is fixed to the shelves either by spaced self-tapping screws or by spot welds. In the nonconcreted stage the deck and joists form a stable structure on which construction loads are safely supported.