In order to avoid the lateral thrust of arches upon the walls, various systems have been proposed in which hollow bricks or tubes are suspended by means of T or L irons between I joists, and the spaces between and above them filled in with concrete.
1 Used at Grosvenor Hotel.
Systems with Hollow Bricks or Tubes. HOMAN AND RODGERS' SYSTEM (Figs. 243, 244) consists of purpose-made hard burnt bricks with moulded projections, protecting the iron joists upon which they rest, and filled in with concrete.
Fig. 243. CROSS SECTION.
Fig. 244. Longitudinal Section.
Fig. 244 is a longitudinal section, and Fig. 243 a cross section, of the floor.
Fig. 245. Fawcett's System.
Faweett's system (Figs. 245 to 247) consists of Fireclay or red clay tubes, or, as they are called by the inventor, "lintels," of the section shown at L, Fig. 247, which rest upon the lower flanges of wrought iron rolled I joists 2 feet apart. The lintels are placed obliquely between the joists - their own diagonals being at right angles to the joists. The spaces between and above them are then filled in with concrete - their lower sides are grooved as a key for plastering.
Fig. 246. Fawcett's System.
Longitudinal section G, H, showing the tubular lintel encasing the joist, and the admission of cold air into the end of the tubular lintel.
Fig. 247. Fawcett's System.
Transverse section C, D, showing the ah passage under the joists and the admission of cold air into the side of the lintel.
The weight of the floor is taken by the joists and concrete, the lintels acting merely as a permanent centering and casing to the ironwork, which is well protected.
This system has been used for a warehouse in Southwark.
One form of this system is given in Fig. 238, which shows the construction recommended by Mr. Hornblower for a floor to carry as much as two tons per superficial yard over a bearing of 18 feet. A A are large hollow fireclay tubes ; B B are smaller tubes of the same material, containing iron I girders as shown, and filled with fine Portland cement concrete, gauged 4 to 1 ; concrete is also packed in between and over the tubes ; P P is the plaster ceiling below, the key for which is afforded by indentations or grooves formed on the lower side of the tubes.
Fig. 248. Hornblower's System. Girders filled in with Concrete.
In these systems there is no thrust upon the walls, and they are efficient if the ironwork is well covered by non-conducting material.
Fox and Barrett's Floors consist of wrought-iron girders placed about 20 inches apart, at right angles to which, and resting on their bottom flanges, are laid rough fillets or strips of wood 1 inch or 1¼ inch square, and about ½ inch apart. Concrete is then filled in between the joists - being supported by the fillets - which form a key to the plastering of the ceiling below.
Fig. 249. Cross section.
Fig. 250. Fox and Barrett's System. Longitudinal section.
In order to avoid all inflammable material, small earthenware drain pipes have been used instead of wooden fillets.
Fig. 249 shows a transverse section, and Fig. 250 a longitudinal section, of such a floor.
G G are the wrought-iron girders, ff the fillets, P the plaster of the ceiling below.
The surface of the floor in the example shown is covered with boards laid upon the joists,jj, which are embedded half their depth in the concrete, and cut to a dovetail section to keep them firm.
Sometimes the concrete is filled in only up to the upper surface of the girders, and floor joists or paving laid upon it.
The concrete used for fireproof flooring of this kind should be of a quick-setting lime or cement, for until it has set its full weight comes upon the girders, but when it is solid it forms a series of flat arches between the girders and strengthens the floor.
If the concrete is thick, it should be applied in two layers to hasten its drying.
Care must be taken that the floor has a good abutment on each side, or is well tied together.
When the lower flanges of the girders are so wide that they would interrupt the key of the plaster and prevent its adherence, light ceiling joists are sometimes secured to the under side of the fillets at right angles to them. These are lathed and plastered in the usual way.
a, With I Girders. The first of these (Fig. 251) consists of wrought-iron or steel I joists, spaced from 18 inches to 3 feet apart, and trussed by pairs of rods about 18 inches apart, as shown in Fig. 251, which clip on to the lower flanges of the girders. Concrete made of coke breeze, mineral sand, and Portland cement - known as "pumice concrete" - is filled in and around the girders and rods. Among the advantages claimed for this floor are the composition of the concrete, which makes it 25 per cent lighter than ordinary concrete, also that if parts of the concrete are damaged the remainder is kept in position by the truss rods.
Fig. 251. Lindsay's System with I Girders. Cross section for boarded floor with embedded sleepers.
This system has been used for the Branch Bank of England, Royal Infirmary (Liverpool).
b, With Trough Girders (Fig. 2 5 2). In this system wrought-iron or steel girders of trough section riveted together are filled in with "pumice" concrete. "When there is no substantial ceiling the lower surface of the ironwork is open to the action of fire, but this may be avoided by fixing pumice concrete blocks or slabs below instead of an ordinary plaster ceiling.
Fig. 252. Lindsay's System with Trough Girders. Section of floor with concrete blocks under.
This system has been used at the National Liberal Club, Prudential Assurance Company (Brook Street), Messrs. Maples, Dublin Museum, and by several Railway Companies.1
In this, ¼ or 3/8-inch rods, about 18 inches apart, are strained through holes in the webs of the joists, and fixed to the walls. A network is thus formed, and concrete is filled in around and below the joists so as to protect them. This system is also used for roofs.
Slabs of Pumice Concrete laid upon the lower flanges of joists, and formed with a projecting piece below to protect those flanges, make a fireproof floor which is quickly carried out.
For Lindsays Arch System, see p. 139.
Pierson's System, formerly Gardner, Anderson, and Co.'s., is practically the same as Lindsay's I girder system with the truss rods omitted.
Moreland's System is practically the same as Lindsay's trough system, but that the section of the troughs is rectangular instead of splayed.
Dawnay's System consists either of ½-inch square iron bars 12 inches apart, or of small 3-inch joists 16 inches apart, resting on the lower flanges of 5-inch binding joists in 7-inch bays; concrete of broken brick and Portland cement is filled in between and around the joists. This construction is suitable for spans up to 30 feet, the binding joists being strengthened according to the increase of span.
This system has been used at the Charing Cross Hotel, Colonial Institute, Exeter Hall, several Board Schools, and other buildings in London.
Allen's.System consists of Portland cement concrete strengthened by iron bars. Bars about 3 inches by 1 inch are placed on edge across the building, 2 feet apart, and built into the walls on either side; across these are placed ½-inch iron rods, also 2 feet apart, thus forming a network with meshes 2 feet square. A temporary scaffold is formed underneath the network, and the concrete - composed of 1 Portland cement to 4 of clinkers, slag, etc. - is thrown in to a depth of 4 inches; when it is set the scaffolding is removed.