(Specially written for FIRE AND WATER.) (Concluded.)
ONE very modern type of fire-resisting floor makes use of triangular lintels, which pass from joist to joist and rest on the lower flange, whose under surface they cover. The older type is shown in figs. 14, 15, while the newer is illustrated in fig. 18.
Figs. 16, 17, and 18 show a combination of lintels, all flat, of T section, and corrugated iron permanent centering. Fig. 19 is a floor of solid concrete, with terra cotta casings to flanges —a form of floor which of course, calls for temporary centering. The concrete is absent in fig. 16, but is shown in fig. 18.
In fig. 20 clay shields protect the lower flanges of the joists and support a corrugated permanent centering for the concrete—there bring besides a suspended ceiling of wire lathing and plaster.
In figs. 21. 22, and 28 concrete blocks of adamant or other equally fire-resisting cement, with breeze or other aggregate, form the lintels, which are also somewhat reinforced by the insertion of steel laths. A concrete filling is laid on these lintels, which vary slightly in form, ns will be seen from the accompanying illustrations.
Other floors, as in fig. 24, are made of loose fireclay bricks which inclose the flanges of the joists and form corbels, on which the hollow fireclay lintels rest— these serving as the permanent centering for a slight finish of concrete. Others, again, as in figs. 25, 26, consist of two hollow tubes between each pair of joists, with a concrete filling-in, limited in amour aud forming the key between the tubes, or a systei of cellular tubes between the joists is adopted, who* special feature is the use of gypsum lintels or cellule tubes.
In the case of domestic buildings and those in whic the floors are not intended to carry any great weight or are of small spans, concrete slabs, with expanded metal or other lathing or iron rods may be employed. Some architects and builders make use of wood beams set diagonally in such a way as to act as skewbacks, in which are set concrete slabs or arches of the same material.
Sometimes also a flat floor or (more frequently) one which is arched in section, consists of plain roofing tiles, and in three or four courses laid in cement, and breaking joint with or without a finish of fine concrete on top. This method, however, is out of date, and was chiefly used for corridors and other situations where the span of the floors is inconsiderable.
In England other and cheaper forms of “fire-resisting” floors are often employed. Some are constructed of ordinary wooden joists nailed together—and this practically forming a solid floor; or the space between the floor joists of the common and usual class is blocked in solid with wood at the lower part of the joints, to which is occasionally added a layer of concrete. “Pugging” on fibrous plaster slabs sometimes or laid on metal lathing without rough boarding and nailed to the underside of the wood joists is not uncommon, or the cellular gypsum slabs already alluded to protect the underside of an ordinary woodenjoisted floor,for which purpose also areemployed various combinations of special fli’e-resisting plasters, such as asbestos, fibrous, or silicate cotton plaster, adamant, and other cements, and special lathings, such as the expanded metal already referred to or flat ribbons interlaced in lattice fashion and inserted between their interlacing. One class of metal lathing (“Thimil”) consists of flat sheets of metal cut, and bent up and down to form projecting stripes, w’hereby is left space for keying. In another style woven iron wire is studded with terra cotta at its intersections.
Of^the concretes specially intended to resist fir more thoroughly than the ordinary concrete are gypsum concrete and one in which Kieselgulir (into which silicate enters extensively) is very commonly employed.