Composite floor structure using steel beam with web openings and the construction method

A composite slab structure using a steel beam with a web having web openings and a construction method of a composite slab structure are provided to fulfill various functions of slabs by securing a space for an access floor sufficiently or a space for lower arrangements, thereby installing an underfloor air distribution system. A composite slab structure using a steel beam with a web having web openings includes a slab unit(100) having a deck formed on the top of a lower flange of a steel beam(200) with a web having web openings(240) or installed over the web, and slab concrete(400) laid with upper reinforcing bars(300) arranged in the slab unit continuously via the web openings of the steel beam and placed to connect web openings. A construction method of the composite slab structure comprises the steps of installing column structures at regular intervals, installing a steel beam with a web having web openings between the column structures, installing a slab unit on the top of a lower flange of the steel beam, arranging many upper reinforcing bars on a lattice bar of a deck in the installation direction of a deck using a spacer to overlap with each other via the web opening of the steel beam, and placing slab concrete on the deck to be lower than the bottom of an upper flange to utilize the space between the top of the slab and the upper flange of the steel beam as a space(A) for an access floor to install air conditioning equipment of an underfloor air distribution system.