In 1833, in building the Mutual Life Insurance Building in New York, a 9-inch flat-tile arch was used throughout, where each tile had one vertical and one horizontal web, and a special fiat tile Wally confined to the last decade. Its sudden development was largely due to the invention and perfection of concrete steel construction. :Mod ern concrete fireproof floors consist of concrete arches, either flat or curved, containing an imbed ded network of steel. Plates of concrete when subjected to bending loads are deficient in ten sile strength, and the purpose of the imbedded network is to supply this deficiency. Plaster composition floors are also usually constructed with imbedded metal network.
In 18S3 the modern era of tall skeleton build ing construction began in Chicago, and thence spread throughout the United States. The abso lute necessity of making these enormous struc tures fireproof has been one of the strongest influences in developing the present system of fireproof construction. The modern steel skele• ton building consists of a steel framework or skeleton covered with a skin and integument of masonry and fireproofing. All of this integu ment is supported by the steelwork except that sometimes the exterior walls are made self. supporting. Foundation construction for tall buildings is described in the article on TIONS. The steel skeleton consists of a series of steel columns rising from the foundations and surmounted by the roof framework. At each floor the columns are braced together in a horizon tal plane by the girders and braces of the floor framing. Where wind-pressures are to be feared, certain of the columns are braced together in a vertical plane by wind-bracing. The steel skele ton of a tall building is structurally independent of the walls, flooring, partitions. and roofing. As it stands, it is incombustible. but not fireproof, since a sufficiently hot fire will cause the steel to expand, twist, buckle, and be otherwise dis torted to the extent of practical destruction. The purpose of the fireproof integument is to pro tect the steel from heat in case of fire, by covering it or imbedding it in a material which is indestructible by fire and a poor conductor of heat. The fireproofing of a steel skeleton build ing comprises, therefore, the following principal items: Fireproof floor construction; column pro tection; fireproof partitions: roof and ceiling protection; and exterior wall construction. Keen ing in mind that, so far as the matter of fire proofing is concerned, the object of each of these items is to keep fire and heat away from the steelwork and prevent the rapid approach of flames, attention may be turned to the general details of fireproof construction as it is practiced in modern tall buildings. Only general methods can be described here: for details, one of the special treatises mentioned at the end of this article should be consulted.
As stated above, the framework of the floors consists of a system of girders and floor-beams supported by the columns; the girders carry the floor-beams. which are spaced about five feet apart. To fill the spaces between these beams and girders and to protect them from fire, arches of hollow tile, concrete, or other fireproof materials are built. These arches are made in a variety of forms, but in all forms the purpose is first to span the opening between the floor beams with a fireproof material which is strong enough to carry the floor-loads; which will not stiffer structural injury from fire: and which is so designed that when the floor is completed every portion of the steel framework is covered by the fireproof material and thus protected from the direct action of the fire. Next to the floor
framing, the most important part of the steel skeleton requiring protection is the columns. The variety of forms of columnar protection is almost as great as the variety of forms of floor systems. With all forms, however, the object is to inclose the column in a ca. ing of fireproof ma terial which is thick enough to prevent the access of destructive heat to the steel.
Roof protection usually consists in constructing a fireproof ceiling below the roof-framing, which cannot be penetrated by fire, and to make the upper extension of the side-walls and the roof covering similarly proof against the passage of fire; the steelwork is thus inclosed in a box or shell impermeable to fire. Another method less coin monly employed is to incase each member of the roof-framing in fireproof material. Par tition construction varies with the kind and form of material used. Tiles or plaster-block partition fireproofing are nsually laid up with mortal exactly like a brick wall; metal or plaster or concrete partitions consist, of a metal or timber studding carrying metal laths on each side which is covered with plaster. The chief object of making partitions fireproof is to confine the fire to the room in which it originates, or at least to retard its spread from room to room. The floors are supposed to retard its spread from one story to another. Floors and partitions must, however, have doors, stairway openings, elevator shafts, etc., to permit communication from room to room and from floor to floor. This has led to considerable search for sonic practicable means of closing such openings, but so far none has been devised which meets with sufficient favor to have been generally adopted. So far as fire proofing is concerned, the exterior walls have the duty to perform of protecting the exterior col umns and preventing the access to the building of flames from the outside. Exterior walls are usually built of stone, brick, or terra-cotta, or a combination of these materials. They must necessarily have windows and doors, and these are their weak points as regards protection against the penetration of flame from the outside. To remedy this weakness, various forms of fire proof door and shutter construction have been developed.
Besides the structural features which have been described, modern fireproof building con struction comprises, as an essential, equipment for the fighting of fire. Such buildings are near ly always provided with lines of standpipes ris ing from the street to the roof and provided with hose connections and lines of hose on each floor. These standpipes are so arranged that they can be connected either with the pumps belonging to the building or with fire-engines located in the street. The last few years have furnished several examples of fires in fireproof buildings. These fires have, on the whole, established the value of such construction, although they have also shown that many weak points exist in modern methods of fireproofing.
At the present time the building regulations of all large cities recognize fireproof construction of buildings, and prescribe the methods in which it shall be carried out and the material which shall be used. The building code of New York City, adopted in 1S99, contains probably the most comprehensive set of regulations governing fire protection and fireproof construction yet enacted by any American city. As these requirements illustrate modern American fireproof building practice, they are given nearly in full herewith.