floors
The tiers which divide a building into stages are called storeys or floors. The function of the floor is to carry the weight of the occupants and their possessions. The floor is the lower horizontal surface of an enclosure which shows different levels or planes of rooms, one above the other. The floor may be a prepared surface of the ground or an elevated area. In modern buildings the floor areas rest on the ground and are insulated from moisture by replacing the top soil with coarse gravel or crushed rock. Wood, steel, concrete or a combination of these materials may be used in the construction of the floor. The finished floors are usually hardwood strips (oak or maple) having at 1/4 in. face width, and tongued and grooved at the edges and ends. The strips are nailed through the tongue to the underfloor by nails. The strips are laid at an angle with the underfloor and parallel to the partitions or outer walls. When the flooring strips are laid they must be covered with sand to remove all inequalities at the edges and to provide a smooth clean surface for the finish. The finish consists of filler covered with a built-up surface of well polished wax. The floors of multistoried industrial buildings carry heavy loads (including the floors of commercial buildings and schools carrying light loads) and may be constructed of reinforced concrete slabs supported directly on columns or carried on concrete or steel beams attached to supporting columns. For lighter constructions steel panels or light steel joists supporting a light concrete slab or fill may be used. For the finished floor (the upper or wearing surface) wood, cork, linoleum tile and masonry (that is marble, brick, slate, flagstone) have practical and aesthetic qualities. a) Classification of Floors Floors for usual residential purposes are mostly made of timber and may be divided into:1) Single-joisted floors.
2) Double-joisted floors..
3) Triple-joisted floors. Loads on floors consist of:
1) The dead load or weight of the floor itself.
2) The superimposed load.
1) Single-joisted Floors are the floors where the total weight upon a floor is carried by a single system of joists: the joists are usually fixed 12 inches to 15 inches from centre to centre of joists. For single floors, the weight of the dead load is about 20 lbs. per square foot. Joists for floors must not only be strong enough to support the loads for which they are designed, but they must be stiff enough to avoid the cracking of the plaster ceilings attached to them, and also to eliminate vibration as far as possible.
2) Double-joisted Floors. Where the smallest span exceed 15 feet, it is better to employ double floors. They consist of girders usually placed across the shortest span, and joists crossing them at right angles and fixed in the direction of the longest span. The main girders may be of wood, steel joists, or Ferro-concrete. Steel joists and girders are more economical, especially for the large span and resistance of fire..
3) Triple-joisted Floors. For spaces on 25 feet and more in timbers, the main girders require lateral support. Intermediate beams are introduced into the main girders and they support the bridging joists. Where floors of this type are employed, the main girders must always be of steel. b) Ventilation of Floors All timbers of floors should be well ventilated; first the timbers near the ground, because damp gases from earth can make them rotten. To provide the necessary ventilation, air flues are constructed communicating between the space under the floor boards and the outer air. In any position where floors are partially or entirely covered with paper, carpet, linoleum or other impervious covering to prevent destruction by dry rot, the necessary ventilation may obtained by the introducing of iron or terra-cotta bricks at intervals in the outer walls between the ceiling and the floor boards level. As a rule those conditions of ventilation and light which are favorable for people are also useful for the preservation of timber.
