Within a few years several styles of fireproof floor construction, based upon the use of concrete in combination with iron or steel in various shapes, have been introduced in this country, and a few of them have proved strong competitors of the hollow tile floor. The chief aim in the introduction of these systems has been to obtain a floor that shall have the strength and fireproof qualities of the tile floor, and at the same time be lighter and less expensive.
There are two general classes of concrete floor construction. The first class consists of tension member floors, which in themselves furnish the necessary strength for sustaining the floor from wall to wall, or wall to girder, without the use of floor beams; and the other class consists of I-beams 5 or 6 feet apart for sustaining the floor, with rods or bars suspended or resting upon the beams, supporting wire cloth, netting or expanded metal, which carries the concrete or plaster filling. Prominent among the first devices mentioned are the Hyatt ribbed metal ties and Portland cement concrete floors built by P. H. Jackson, San Francisco; the concrete and twisted bar floors built by the Ransome & Smith Company, of Chicago; and the Lee hollow tile and cable rod floors built by the Lee Fireproof Construction Company, of New York.
Prominent among the I-beam and concrete filling devices are the systems of the Metropolitan Fireproofing Company, of Trenton, N. J.; the expanded metal construction companies of St. Louis and New York, the arch construction of the Roebling system and the flat beam construction of the Columbian Fireproofing Company.
While concrete has been used in construction to resist compressive stress for many centuries, it was not until 1876 that an attempt was made to form concrete beams by imbedding iron in the bottom to afford the necessary tensile strength which the concrete lacked. The idea was conceived by Mr. Thaddeus Hyatt, an inventor, who made many experimental beams, with the iron introduced in a great variety of ways, as straight ties, with and without anchors and washers; truss rods in various forms, and flat pieces of iron set vertically and laid flat and anchored at intervals along the entire length. These experimental beams were tested and broken by Mr. David Kirkaldy, of London, and the results proved that the iron could be perfectly united with the concrete and that it could be depended upon for its full tensile strength.
The method Mr. Hyatt finally adopted as the best for securing perfect unison of the iron and concrete was to use the iron as thin vertical blades placed near the bottom of the concrete beam or slab, and extending its entire length and bearing on the supports at both ends; these vertical blades to be anchored at intervals of a few inches by round iron wires threaded through holes punched opposite each other in the blades, thus forming a gridiron, which was completely imbedded in the concrete.
The first person in this country to make a practical application of Mr. Hyatt's discovery was Mr. P. H. Jackson, of San Francisco, Cal., who has used a combination of concrete and Hyatt's ties quite extensively in that city for covering sidewalk vaults and for the support of store lintels; also for self-supporting floors.
Tests of concrete beams made by Mr. Jackson are described in the Architects' and Builders' Pocket Book.