FIREPROOF CONSTRUCTION FLOORS Ten years ago the public knew comparatively little of the merits of cement concrete for fire proofing purposes. There was at that time a greatly increased demand for a homogeneous fireproofing material which could be scientific ally and expeditiously made; which would be come uniform throughout the floor, in irregular places as well as in square panels; which would unite with and protect all parts of steel members from rust as well as from heat; which could be designed to carry any desired load; which could be made in any shape to suit conditions; which could be made in the lightest forms to save the weight of supporting steel.
Since the New York City building laws of 1899, every form of fireproof construction made of cement concrete has had to pass very rigid tests prescribed. All the cement concrete fire proofing now installed in New York City has been subjected to the several tests and has had the approval of the Superintendent of Buildings.
The requirement of four hours of heat much higher than ever attained in a building conflag ration, followed by the regulation stream of cold water under high pressure, all on a loaded full sized floor panel, finally loaded to 600 pounds per square foot, was sufficient evidence of the merits of the material, as a fireproofing, to everyone witnessing these tests.
After the fire test, and the approval of the construction, any such flooring, designed to carry more than a safe floor load of 150 pounds per square foot, was subjected to a load test of ten times the safe load required. The testing of this form of construction was persisted in by the Department of Buildings, by architects, and by engineers for several years, and the success of these tests was phenomenal to all concerned.
On account of the lightness of cinders and the peculiar elasticity of the concrete from them, to expand and contract in resisting heat, cinder concrete fireproofing has largely been used for floor-slabs between steel beams.
Cinders make good fireproof concrete and this material may be used for suspended ceilings and as a filler on top of slabs between furring strips. Sometimes cinders contain unconsumed
coal, which is bad when concrete is mixed wet, and is a dangerous element in case of fire. Cin der concrete should be used strictly as fireproof ing and not as a structural material. Used in the latter way, it is costly and dangerous. Some times a 1:2:4 mixture is used with a fiber stress of 200 pounds per square inch (thus classing it with burnt clay), but it is not good practice, so cannot be recommended. The cinders should be carefully selected and freed from ashes, etc. In the majority of cities, cinder concrete cannot be used in spans exceeding 4 to 6 feet. When greater spans are permitted, they are never more than 10 feet, and must be designed after testing a sample slab or beam to destruction, and using data thus obtained with a factor of safety of ten. The ultimate strength of good, well-made cinder concrete is about 900 pounds per square inch in compression at the end of thirty days with a 1 :2 :4 mixture.
Improvements in recent years in the prac tical manipulation of centering, mixing, han dling, and reinforcing cinder concrete have greatly facilitated and cheapened its construc tion for fireproof floors. It is now recognized as one of the speediest and most convenient forms of floor construction. There are at present no fireproof contractors—not even those who formerly used other kinds of concrete exclu sively, who do not construct largely of this material.
Illustrations of solid concrete and cinder con crete filled fireproof floors may be found in many of the figures and systems shown in this volume. Special reference might be made to Figs. 98 and 103, in the preceding volume.
A building to be fireproof must be so con structed that it is not only non-combustible, but also that it will not be seriously damaged by the burning of its contents. That is, a fire-resisting building material should fulfill the following re quirements: 1. It should be non-combustible.