=17.= The cost of =reinforced-concrete buildings= varies with
the market price of cement and the steel bars or metal used for
reinforcing. At present, reinforced-concrete buildings of the
factory type constructed of common, hard, stretcher-brick walls and
reinforced-concrete floors, roof, and columns with foundations may be
built for from $1.35 to $1.65 per square foot of floor area. Usually,
the height of ceilings in factory buildings is about 14 feet from floor
to floor, thus making the cost of this type of building approximately
from 10 to 12 cents per cubic foot. For buildings of a better
commercial type, with face-brick walls and terra-cotta trimmings, the
cost per square foot of floor area will range from $1.65 to $1.90,
making the cost per cubic foot from 12 to 14 cents.
Reinforced-concrete buildings, as a rule, exceed the cost of buildings
of slow-burning construction of the same size by an amount about equal
to the cost of the metallic reinforcement. In other words, a building
of reinforced concrete costs from 10 to 25 per cent. more than the same
building of slow-burning construction.
The price of reinforced concrete per cubic yard varies within wide
limits, depending on the mass of concrete employed and the intricacies
of the forms. In building construction, reinforced concrete, including
the price of the forms, can usually be placed for from $12 to $18 per
cubic yard, the cost of the steel reinforcement being added.
Where the building is of considerable height, the same forms used in
the three lower stories may be used in constructing the balance of
the building. In such a case, the cost of the forms will probably not
exceed $6 for each cubic yard of concrete placed. If the building is
only two or three stories in height, and the work is rushed by using
new centering in each floor, the cost of the forms will range from $7
to $9 per cubic yard of concrete.
The cost of form work for floor construction will range from 10 to 12
cents per square foot. Column forms will cost in the neighborhood of
20 or 25 cents per running foot. The forms used for fine concrete-wall
construction require considerable time and bracing, and generally must
be executed with great care where finished work is required. Such forms
will cost from 8 to 10 cents per square foot of form on both sides
of the wall, but will greatly exceed this price if molded courses or
paneled spandrels are to be formed and lettering is to be cut in the
work.
=18.= In estimating the cost of =reinforced-concrete slabs=, the
cost of the centering, the concrete, and the steel reinforcements
must be considered. The cost of centering for slab work varies from
5 to 7 cents per square foot, the latter figure probably being
more nearly correct for usual conditions. The concrete for plain
reinforced-concrete slab construction on steel beams can be placed for
about $5.60 per cubic yard, or 1¾ cents for a square foot 1 inch in
thickness. At present market values, the steel for reinforcing slabs
can usually be considered as costing about 3 cents a pound, the pound
price increasing as the rods decrease in size.
Table III gives the approximate cost, in cents per square foot, of
constructing different thicknesses of reinforced-concrete slabs on
steel-beam construction with the different sizes of reinforcing bars
usually employed. The prices include cost of centering, concrete, and
steel reinforcement.
=19.= Table III cannot be used for estimating the cost of a
reinforced-concrete floor with reinforced-concrete beams and girders.
In the construction of such a floor, the centering is much more costly
than where steel beams are used for the support of the floor slab. On
an average, the centering for the reinforced-concrete floor systems,
including the studding and shoring, will cost from 20 to 22 cents per
square foot, the sides of the beam and girder forms being included
in the square-foot estimate. This cost is materially reduced where
the centering is used over and over again for the construction of
upper floors, so that where the building is six or eight stories in
height, the average cost of the centering will not exceed 10 or 12
cents per square foot, including shoring, as just mentioned. Owing to
the difficulty encountered in placing the concrete in the beams, the
tamping required with slice bars, etc., and the expense of placing
the reinforcement, the concrete for such construction will cost about
$7.50 or $8 per cubic yard. The steel for the entire construction
will usually average from 3 to 4 cents a pound, depending on whether
plain rods or deformed bars are used, or whether the system is made
up of loose rods or fabricated frames. In estimating the cost of
such a floor system, the centering should be figured by a carefully
itemized estimate, or roughly from the preceding figures. The amount of
concrete in both the slab beams and columns should be estimated, and
the total number of cubic yards required for the entire work should be
determined; then the unit price for providing and placing the concrete
should be carefully considered with reference to local conditions of
labor and cost of material.