This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
The size and spacing of the floor beams will depend upon the style of floor construction which may be adopted. The original fireproof floor consisted in spacing beams five or six feet apart, and turning a brick arch from flange to flange of the beams, as in Fig. 213. The space above the arch is filled with concrete up to about an inch above the beams, completely enclosing the steel; and screeds running parallel to the beams, bedded in the concrete, give a sufficient nailing for the floor boards. The ceiling underneath may be finished by simply plastering on the underside of the brick arch, or a level ceiling may be hung to the rough floor. As an arch of this shape will exert considerable thrust, this must be taken up by the use of tie rods 5/8-inch or 3/4-inch in diameter, spaced along below the center line of beams at intervals of about six feet. This style of flooring will weigh about seventy pounds to the foot, and has been practically superseded by the lighter constructions employing terra-cotta arches or concrete.
Fig. 213. Brick Floor Arch.