A first-class wood floor is made as follows: Excavate the soil to a depth of 18 ins. and place a thoroughly rammed layer of concrete 8 ins. thick on the bottom. After this layer of concrete has set place 6x6-in. sleepers of pine or spruce 3 ft. apart c. to c. and fill between them and flush with their tops with a second layer of concrete. For a wearing surface lay a flooring of 3-in. plank spiked to the sleepers. Fig. 14 is a section of floor of this construction. This floor construction is heavy and solid and will carry ordinary machinery without special machine foundations.
Fig. 14. Heavy Timber and Concrete Floor.
A much lighter and cheaper wood floor may be constructed by embedding 3-in. plank or half-round sleepers in a layer of 6 ins. or 8 ins. of cinders and spiking to them a flooring of 3-in. plank (Fig. 15). When this construction of floor is used all machines must be provided with special foundations. Wood block pavement on a concrete foundation is a form of shop floor which has been considerably used, but the writer cannot recommend this construction.
Car sheds for electric railways require a special floor construction because of the pits beneath the tracks for the use of the inspectors and cleaners. These pits are from 4 ft. to 5 ft. deep. A common construction is to build brick piers nearty to the height of the floor level which carry timber sills, to which the floor planking is spiked.
Fig. 15. Light Timber and Concrete Floor.
Where wood floors are employed the preservation of the timber from decay is an important consideration. The best authorities on the question recommend the application of a coating of lime 1/2-in. thick around the sills and on the bottoms of the floor planks. This protection should give the floor a life of 50 years. Mixing coal tar with the concrete makes a good preservative, or the concrete may be covered with tar wherever the floor timbers come in contact with it Coating the sills and the underside of the planking with rosin is another excellent means of preventing decay.
There is probably no more substantial a construction for floors above the ground floor than the riveted steel trough construction known as the Lindsay floor. With this construction the floor boards may be laid directly on the metal or they may be spiked to small timber sills embedded flush in a concrete or cinder filling carried by the troughs, as shown by Fig. 16. The "Hand Books" published by most of the rolling mills give the safe load per square foot of trough flooring for various spans.
A cheaper construction of iron floor than the steel trough consists of corrugated iron arches sprung between I-beams and filled above with concrete in which the timber sills are bedded and planked over, as shown by Fig. 17. This floor has no spring. Corrugated iron sheets of No. 18 B. W. G., having a span of 6 ft. and a rise of 10 ins., have in actual tests sustained a load of 1,000 lbs. per square foot. Brick or terra cotta arches filled above with concrete is a floor construction which has been much used, but besides being heavy and expensive, this construction cannot be recommended for floors which are subjected to vibration from heavy running machinery. Fig. 18 is a section of brick arch floor.
A floor construction which has been extensively employed consists of a timber flooring carried by metal beams or girders. Fig. 19 shows one form of this construction, which consists of steel I-beams spaced 3 ft. or 4 ft. apart and capped with timbers to which a flooring of 3-in. or 4-in. plank is spiked. Another form of this construction is shown by Fig. 20, which consists of built up steel girders capped with plank and carrying timber joists to which the plank flooring is spiked. In this construction the girders are spaced from 10 ft. to 15 ft. apart. Another form of I-beam and timber floor construction which is not much used in this country but which is a very efficient construction for heavy loads is shown by Fig. 21. The I-beam joists are spaced the proper distance apart, which should be not more than 3 ft. or 4 ft., so that the depth of the wooden flooring may be kept at the minimum, and on them planks are set close together on edge and firmly spiked together. The top of this planking is then covered with a 1/2-in. coating of fine sand mortar and a wearing surface of matched boards is laid on top of it.
Figs. 16 to 22. Typical Upper Floor Constructions.
A form of floor construction known as "slow burning construction" is shown by Fig. 22. The principle of this construction, which is entirely of wood, is to concentrate the timber into the fewest number of large pieces so that a minimum surface will be exposed to the attack of flames. The construction consists simply of widely spaced heavy timber joists covered with a flooring of heavy planks.