[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.
TABLE III
COST IN CENTS PER SQUARE FOOT OF
REINFORCED-CONCRETE FLOOR SLABS
SUPPORTED ON STEEL BEAMS
CEMENT CELLAR FLOORS
20. In determining the cost of cement cellar floors, the concrete proper and the top coat should be considered separately. The concrete proper is usually reckoned by the cubic yard. About 1 hour more is required to lay a cubic yard of floor than is necessary for plain concrete work. Therefore, in estimating, 25 cents per cubic yard, or the wages of a laborer for 1 hour, must be added to the figures given in [Table II]. A 1-3-6 mixture is generally used. For stone concrete, then, the cost of the concrete proper for a cement cellar floor would be $5.17 per cubic yard, exclusive of the cost of supervision and the builder’s profit.
An analysis of the cost per square yard of top coat 1 inch thick for a cement cellar floor is as follows:
| Cost Cents | ||
| ¼ | hour, plasterer’s time, at 45 cents per hour | 11¼ |
| ¼ | hour, laborer’s time, at 25 cents per hour | 6¼ |
| ¹/₁₅ | barrel of cement, at $2 per barrel | 13⅓ |
| ⅛ | barrel of white sand, at 75 cents per barrel | 9⅜ |
| Approximate cost per square yard | 40 |
To the foregoing should be added the cost of supervision and builder’s profit.