according to the weather and the nature of the cement, and care must be taken that the freshly laid tiles are not too heavily loaded

888888888888

Fig. 235. Segmental Terra Cotta Arch

with materials until they are hard. If the arches are to be plastered upon for a ceiling, they must be kept clean, or bad stains are likely to appear. All holes or irregularities on the underside must be filled with cement mortar to give a proper surface for plastering. Where a flat ceiling is not required, but strength is the main factor to be observed, segmental, tile arches are often used, Fig. 235, made with a rise of an inch to the foot, up to 20 feet of span. They are employed to a great extent in warehouse construction.

While the nature of floor tiles does not permit a fine joint to be made, they should be laid as closely as possible, especially the key blocks. Joints as great as a half-inch should not be permitted, and the tiles should be set in place by being shoved together as in brick laying. Unless the building is closed in, floor tiles cannot be laid in cold climates when there is danger of freezing and thawing, as the joints are likely to be affected to the extent of causing deflection, if not more serious trouble.

Floor arches are often tested by applying a heavy roller to them after the wood centers have been removed, and by dropping a heavy block of timber upon the arch, a 2-inch bed of sand being previously spread over the tiles to prevent mechanical damage.

Concrete Floors. The use of concrete for floors has become an important factor in the construction of fireproof buildings. Con

crete floors combine the qualities of strength and ease of construction with lightness, and are less expensive than most of the hollow

tile constructions. Concrete so used is generally found in combination with steel or iron in some form or other; it is to the reinforcing material that the concrete owes its tensile strength.

Fig. 237. Section of Expanded Metal Floor

Concrete floors may be considered under two principal classes, one in which the concrete in combination with steel tensile members forms the whole of the floor construction, Fig. 236, and the other in which steel I-beams are set as for brick or tiles, the spaces

Fig. 238. Section of Roebling Floor

being filled in with concrete, either in the form of a plate, Fig. 237, or supported upon an openwork metal base, Fig. 238.

A newer type, which partakes of the characteristics of either or both of these forms, employs hollow forms of corrugated or perforated steel or of some plaster

holding composition so spaced as to divide the floor into a series of beams or panels made by the concrete filling which is poured between and over the hollow forms as centering, the forms shown in Fig. 239 remaining in place in the finished structure. Various patented forms are used in this way so designed as to be adjustable to any length or width, and so arranged that, by spreading, different widths of beams may be obtained. These forms

are called by various trade names such as "Ferro-Domes", "FloreDomes", "Floretyles", etc.

Advantages of Different Types. With many types of flooring available, each possessing merits peculiar to its own construction, the architect is often at a loss to decide upon a special system. Cost, which is an ever-present factor, will decide in many cases, and in others local considerations may require particular methods. In the main, regard should be given to lightness, strength, and fireresisting qualities, as well as to speed of erection and the skill of available workmen.

Of the respective merits of the two general systems of terra cotta and concrete, much has been written, especially with regard to fire-resisting qualities, but the question of the advantage of one over the other cannot be said to have been settled at the present time. For the very high buildings, one of the systems requiring the use of riveted steel floor beams and girders is usually adopted, the beams spaced not only with reference to the load and the requirements of the floor construction, but with a regard to the general strength and stability of the whole building.

Fireproofing. The various parts of a building of steel construction are in themselves of a fire-resisting character, but for the thorough protection of the structure, special devices must be employed.

Columns. Especially is this true in the case of columns, which must sustain great

Fig. 241. Lath and Plas- weight and should, therefore,

ter Column Casing

be adequately protected. Col

umns may be enclosed in concrete or brick, which should be not less than 8 inches thick; or hollow terra cotta tiles may be used, preferably in two layers, each not less than 2 inches thick and breaking joints, Fig. 240. Columns may also be partially protected by the use of metal lathing and plaster in one or two layers with an air space between, Fig. 241.

Floors. Floor beams and girders are protected normally by the floor or ceiling construction, and each maker of floor construction has his own system of fireproofing for girders and columns and

other exposed members, so that, in general, the contractor for the floors will be given a contract for all the other fireproofing in the building.

ROOF AND WALL CONSTRUCTION

Roofs and Ceilings. As the roofs of high buildings are generally made with very little pitch, the same construction may be used here as for the floors, but a special treatment will be required to retain a level ceiling in the upper story. This is usually done by hanging steel T-bars at a level below the roof, upon which a ceiling may be laid either of terra

Fig. 242. Hanging of Terra Cotta Ceiling

cotta blocks to be plastered, Fig. 242, or of metal lathing, Fig. 243. Exterior Walls. The construction of the exterior skeleton of a fireproof building varies according to the covering material. While the adopted type of floors may be carried throughout one or several buildings, by a simple repetition of methods, the construction of the outside frame must be modified to suit the different materials used in different buildings, or often in different portions of the same building.

Fig. 243. Hanging of Wire Lath
Ceiling

The exterior treatment of a building of skeleton construction may be said, in general, to resolve itself into a series of piers, more or less marked in character, which enclose the vertical supports, the space between them being to a great extent occupied by windows, while a horizontal piece of masonry separates the windows of each story and covers the floors.

The masonry enclosing the building is generally supported by the steel frame, and may be of brick or stone, according to design, though concrete and terra cotta in molded or cast forms are also available.

Terra Cotta Covering. The adaptability of terra cotta to the exterior adornment and fireproofing of buildings is so great that its

use has become general in all places where durability and resistance to heat are essential. The ornamental facings cannot always be supported by direct bearing on the steel frame, and so a system of anchors and ties must be devised by which the separate blocks may be held in place.

I

Fig. 244.

For terra cotta finish which has no great projection from the line of support, ties of 4-inch rods may be hooked into the ribs of the terra cotta and secured to the steel frame or the brick filling, Fig. 244; but when a greater projection is required, as for cornices, then small beams or T-irons must be used, well built-in or anchored to the main structure, Fig. 245. Section Showing Method Exterior terra cotta as ordinarily finished is not affected by the atmospheric condi

of Anchoring Terra Cotta

tions which affect stone; but as the surfaces are likely to become warped in the baking, it is necessary to see that no attempt is made to straighten bad pieces by chiseling, as this destroys the surface and exposes the softer interior to the danger of decay.

PARTITIONS

The partitions of fireproof buildings may be built of brick, terra cotta, tiles, or plaster blocks, or of light iron studding with metal

lathing and plaster. Brick partitions,

to resist the passage of fire, must be at least 12 inches thick, and are not, therefore, generally used unless required for floor bearing also. With the column and girder construction which we have had under consideration, a lighter construction than brick is generally desired for partitions.

Partition Blocks. Terra cotta blocks, either of dense or porous terra cotta, make good partitions, Fig. 246;

these are usually made 4 inches thick, and are of the same composition as the floor blocks. They are generally set with the hollows