Fig. 227.—Girder and Slab Forms for 6-Story Building.
Since the lumber was used three times, $30 ÷ 3 = $10 is the charge against each 1,000 ft. B. M. needed to encase the concrete on a floor. There were nearly 34,000 ft. B. M. per floor, hence the cost of lumber ready for erection was $340 per floor. There were as shown below, 200 cu. yds. of concrete per floor, so that the cost was $340 ÷ 200 = $1.70 per cu. yd. of concrete for forms ready for erection. It took a gang of 5 men 7 days to tear down and carry up the forms for one floor; hence 5 × $2 × 7 = $70 per floor, or practically $2 per M. ft. B. M., or $0.35 per cu. yd. of concrete for taking down and carrying forms two stories. It took a gang of 10 carpenters 7 days to erect these forms, which at $3.50 per day was $245 per floor, or $7 per M. ft. B. M., or $1.20 per cu. yd. of concrete.
Concrete.—The amount of concrete per floor was as follows:
| Floor slab 3½ ins. thick, 10,200 sq. ft. | 110 cu. yds. |
| Beams, 10×10 ins. | 40 cu. yds. |
| Beams, 5×10 ins. | 20 cu. yds. |
| Columns, 15×15 ins. (average) | 30 cu. yds. |
| —————— | |
| Total concrete per floor | 200 cu. yds. |
A concrete mixer, a hoist and a gang of 14 men mixed and placed the concrete for a floor in 7 days. At $2 per day for labor this gives 14 × 7 × $2 = $196, or say $1 per cu. yd. for mixing and placing the concrete.
Reinforcement.—In each of the 10×10-in. beams there were 4, 1-in. round rods, 2 straight and 2 bent, and stirrups of ⅛×1-in. straps spaced 5 ins. apart at columns and 15 ins. at the center. In each 5×10-in. beam there was half as much steel as in a 10×10-in. beam. The floor slab reinforcement consisted of ¼-in. rods spaced 5 ins. apart and 2 cross-rods in 7-ft. panel. The column reinforcement consisted of 4 rods averaging 1 in. in diameter. In round numbers the amount of steel required for each floor was, therefore, as follows:
| Lbs. steel rods in 10×10-in. beams | 16,200 |
| Lbs. steel rods in 5×10-in. beams | 4,000 |
| Lbs. stirrups in beams | 3,000 |
| Lbs. steel rods in floor slabs | 3,800 |
| Lbs. steel rods in columns | 1,400 |
| ——— | |
| Total pounds steel per floor | 28,400 |
This is equivalent to 142 lbs. of steel per cubic yard of concrete, or about 1 per cent of the total volume of reinforced concrete was steel. The steel in the beams was about 3 per cent. It required a gang of 5 laborers 7 days at $2.25 per day, to bend and place the steel for each floor or $86 for labor on 28,400 lbs. of steel. This is equivalent to 0.3 ct. per lb., or 45 cts. per cu. yd. of concrete.
Summary of Costs.—Summarizing the figures given we have the following cost per cubic yard of concrete in floors and columns: