Page:The American Cyclopædia (1879) Volume II.djvu/435

BEAM 415 manufactories, &c., and the system is rapidly coming into general use. For filling in between the beams for tire-proof floors various systems have been adopted. In France, where fire- proof construction with iron beams is exten- sively used, the filling in is generally a concrete of refuse materials and plaster of Paris. Beams of the I form are placed 2| or 3 feet apart ; their ends are built in the walls and secured by anchors ; no beams are placed immediately at the walls parallel with the beams. The beam next each wall is connected to it, and each beam connected with the one next adjoining, by inter-ties of round or square iron of about half a square inch in sectional area, and placed 2$ or 3 feet apart ; the inter-ties pass through holes near the centre line of the beams, and are provided with a head at one end and riveted up at the other after they are put in ; the ends that are built into the walls are bent to form anchors. Smaller rods parallel with the beams, and 7 or 8 inches apart, are suspended from the inter-ties, the ends of the rods being bent up so as to hook over the inter- ties, while the rods themselves are on a level but little above that of the bottom of the beams ; or the inter- ties may be supported upon the lower flanges of the beams and be bent up at the ends so as to hook over the upper flanges, and the smaller rods parallel with the beams be laid upon the inter-ties. A flat centring is placed against the bottoms of the beams, and broken bricks or other refuse materials suitable for concrete are put upon the centring ; and plaster of Paris being poured in, the whole mass soon becomes sufficiently set to allow the centring to be re- moved, and the concrete to be sustained by the iron framework between the beams. In some cases the plaster concrete fills up the whole space between the beams, and flooring tiles are laid directly upon it ; in others the depth of the concrete is less than that of the beams, and wooden strips are laid across the beams per- pendicular to their length, to which ordinary flooring boards are nailed. A finishing coat of plaster put directly on the concrete forms the ceiling below. Hollow potteries placed upon the iron latticework, with the interstices filled with plaster, are frequently used instead of concrete. A very light and superior floor is thus made, and the rigidity of the whole system considerably increased. The use of plaster for the filling in between the beams has not been adopted in England or America, be- cause of the greater cost and inferior quality of the plaster that can be obtained. The sys- tem known as that of Fox and Barrett has been used extensively in England. Light strips of wood with narrow spaces between them are supported on the bottom flanges of the beams, and reach from beam to beam. On these strips is spread a layer of coarse mortar, which is pressed down between them. Concrete, made with cement, is filled in between the beams, and a tile or wooden floor is laid immediately upon it. A rough and a finishing coat of plas- 79 VOL. ii. 27 ter are put directly on the cement to form the ceiling below. Floors have also been made by the use of arched plates of wrought iron or of corrugated sheet iron supported upon the lower flanges of the beams, with a filling of con- crete above the arched plates or corrugated iron on which the floor is laid. The sys- tem of light segmental brick arches spring- ing from the lower flanges of the beams and levelled up with concrete is that most gen- erally employed in this country and in Eng- land. It is more strictly fire-proof than any other, and much more economical than the use of arched plates or corrugated sheet iron, and, except in France, where plaster is cheap, than the French system. The weight of the floors themselves forms a much greater part of the total load to be carried by the beams than in the lighter French system ; but on the other hand, the arches and concrete add materially to the strength and rigidity of the beams, not only by preventing lateral deflection, but by adding to some extent the resistance to com- pression of so much of the arches or concrete as is above the neutral line to that of the upper parts of the beams, whereby they become in fact an integral part of the beams themselves. Long beams should be supported in the middle of their length by wooden scantlings until the cement of the arches or concrete is set, in or- der to get the full advantage of this additional resistance. The arches should have a rise of not less than one inch to the foot of span, and are generally the width of a brick in thickness, unless the span exceeds 6 or 8 feet, when they should be 8 inches at the soffit and 4} inches at the crown. If a wooden flooring is to be used, wooden strips parallel with the beams are laid in the concrete filling above the arches, to which the flooring can be nailed. To form the ceiling below the beams, wooden strips may be secured to the lower flanges of the beams, to which ordinary furring, lathing, and plastering can be nailed ; or the plaster may be put directly upon the arches, so as to show the system of construction, and thus with suit- able mouldings a good architectural effect can be obtained. Any inequality in the thrust of the arches on the beams is counteracted by the tie rods perpendicular to the length of the beams connecting them together. The load to be sustained by the floors of dwellings, offices, and buildings, other than manufactories and buildings for the storage of heavy goods, is or- dinarily assumed at 150 Ibs. per square foot. The weight of the beams, arches, concrete, &c., forming the floor, will ordinarily be about 75 Ibs. per square foot, leaving 75 Ibs. per square foot for the variable load. This is as great a load as can be brought upon a floor by a crowd of people. For wrought-iron floor beams the actual or safe working load should not produce a greater strain than 12,000 Ibs. per square inch of section at the part of the beam which is subjected to the greatest strain by the action of the load. In the following part of this