Windows of wire glass in metal frames, sliding or pivoted either horizontally or ver tically, are a part of the complete equipment of a modern reinforced concrete building.
Partitions are of concrete 3 or 4 inches thick, slightly reinforced against shrinkage cracks; but metal lath and plaster terra cotta tile, or plaster lath partitions are more common. Metal lath and plaster partitions 4 inches to 6 inches thick have a framework of steel studding running between floors, upon which is fastened the metal lath, which is then plastered with a mixture of lime and cement mortar in three coats; the first and scratch coat with hair or fibre. The hollow space may be filled with cinder concrete. Metal lath of various com mercial forms with integral projecting ribs need no separate studding. Plaster blocks made chiefly of gypsum, or plaster of paris, with an adinhaturecl fibre are easy to handle and cut, but are not as fireproof as other forms.
Considerable ingenuity is shown in devising forms of light concrete beams, factory made, for floor systems of dwellings.
Floor Loadings.—Concrete will spread heavy loads, on small areas, to adjoining portions not so heavily loaded and thus permits of partial overloads. Such floors are often loaded to as much as twice the design load, and therefore there should be conservative designs to begin with. As a test of workmanship it is common practice to load a simple panel or two adjoining panels with a test load equal to twice the design load plus once the dead load. Floor live loads per square foot to be provided for are (Boston practice) : dwellings and apartment-houses and public hotels, 50 pounds; office floors, and for public rooms of apartment and public hotels, 100 pounds; floors of retail stores and public buildings, except schoolhouses, 125 pounds; schoolhouses, other than floors of assembly rooms, 80 pounds and for floors of assembly rooms t 125 pounds; drill rooms, dance halls and riding schools, 200 pounds; warehouses and mercantile buildings, at least 250 pounds. Concrete floors are designed up to 1,000 pounds per square foot. Ordinarily the increase in loads to allow for impact is small in concrete structures, from 20 to 50 per cent of the live load in bridge floors, and none in arch rings or heavy members.
Reinforced concrete retaining walls ap peared early in the art before 1894. In the L type the vertical stem which holds the trans versely-acting earth pressure is a cantilever. There is also a cantilever transversely act ing horizontal base, projecting back, acting upon which the weight of earth equilibrates the lateral pressure. This type is used up to heights of about 18 feet. Reinforcement runs vertically down the face of the vertical stem next to the earth, and is anchored in the base. Horizontal rods run on the upper side of the base (the heel) and are anchored in the vertical stem. The horizontal base may pro ject in front of the wall to form a cantilever toe with rods in the bottom. Reinforcement in the exterior outward face of the vertical stem provides for shrinkage and expansion. Expansion joints may be provided. In excess of heights of about 18 feet, the counterfort type is used, in which the vertical stem and hori zontal base are connected on the inside by counterfort walls. The vertical and horizontal elements now become slabs carrying earth pressure and weight to the counterforts which are designed as vertical cantilevers, and to which the slabs are well tied. Types of plain and reinforced concrete retaining walls merge into one other.
Abutments for bridges are similarly de signed. Cellular construction in abutments and similar construction in reinforcement concrete is a logical development, by which thin sections, properly reinforced, replace heavy masses.
Reinforced concrete dams have a sloping water tight reinforced concrete deck or slab supported on vertical concrete walls. The water pressure increases, instead of opposes, stability. The sloping deck may continue to rise over a crest and fall to an overfall slab sloping down stream. The two slabs are con nected by vertical walls or buttresses. The deck slab is designed to carry the water pres sure to the vertical walls. The Schuylerville, N. Y., dam is 250 feet long and 25 feet high. Vertical walls, 10 foot centres, 12 inches thick, support a deck tapering from 8 inches to 12 inches thick, while the overfall apron is 8 inches thick. A foot bridge passes under the dam, supported on the vertical walls. Such dams are commonly known as Ambursen dams.