The work was done by the railway company's forces, and Mr. Samuel Rockwell, Assistant Chief Engineer, gives the following figures of cost:
| Total. | Per cu. yd. | |
| Temporary buildings, trestles, etc. | $ 752.33 | $0.15 |
| Machinery, pipe fittings, etc. | 416.34 | 0.08 |
| Sheet piling and boxing | 1,006.12 | 0.21 |
| Excavation and pumping | 1,619.74 | 0.33 |
| Arch centers and boxing | 3,528.92 | 0.73 |
| ———— | —— | |
| Total | $7,323.45 | $1.50 |
| Concrete masonry: | ||
| Cement | 8,860.55 | 1.84 |
| Stone | 1,788.50 | 0.36 |
| Sand | 240.00 | 0.05 |
| Drain tile | 103.03 | 0.02 |
| Labor | 8,091.41 | 1.68 |
| ————— | —— | |
| Total concrete | $19,083.49 | $3.95 |
| Steel reinforcing rods | $ 3,028.39 | $0.63 |
| Engineering, watching, etc. | 508.40 | 0.11 |
| ————— | —— | |
| Grand total (4,833 cu. yds. concrete) | $29,943.73 | $6.19 |
ARCH BRIDGE, PLAINWELL, MICH.—The following figures of cost of a reinforced concrete arch bridge are given by Mr. P. A. Courtright. The bridge crosses the Kalamazoo River at Plainwell, Mich., and is 446 ft. long over all with seven arches of 54 ft. span and 8 ft. rise. The arch rings were reinforced with 4-in., 6-lb. channels bent to a radius of 70 ft. and spaced 1.9 ft. c. to c. The contract price of the bridge was $19,900.
The concrete was made of Portland cement and a natural mixture of sand and gravel in the proportions of 1-8 for the foundations, 1-6 for arches and spandrel walls and 1-4 for the parapet wall. The proportions were determined by measure; the wagon boxes being built to hold a cubic yard of sand and gravel. A sack of cement was taken as 1 cu. ft. For foundations the pit mixture was used without screening; stones over 4 ins. in diameter being thrown out at the pit or on the mixing board. For the arches and spandrel walls the gravel was passed over a 2-in. mesh screen on the wagon box. The aggregate for the parapet walls was screened to 1 in. largest diameter. The concrete was mixed in a McKelvey continuous mixer which turned the material eight times. The mode of procedure was as follows: The gravel was loaded upon wagons in the pit and hauled to a platform at the intake of the mixer. Half of the cement required in the concrete was then spread over the top of the load in the wagon box and the whole was dumped through the bottom of the wagon box onto the platform and spread with shovels. The remainder of the cement was spread over the mixture and the whole was shoveled by one man to a second man who shoveled it into the mixer. Water was added after the mixture had passed about one-third of the way through the mixer. The mixer delivered the concrete directly into wheelbarrows, by which it was delivered to the work. The concrete was spread in layers from 2 to 4 ins. in thickness and thoroughly rammed with iron tampers; two men were employed tamping for each man shoveling. The arches were concreted in three longitudinal sections, each section constituting a day's work. The work was done in 1903 and the concrete cost for mixing and placing:
METHODS AND COST OF CONSTRUCTING A FIVE-SPAN ARCH BRIDGE.—This bridge consisted of five elliptical arch spans of 40, 45, 60, 87 and 44 ft., carried on concrete piers. The arch rings were 12 ins. thick at the crowns and 18 ins. thick 5 ft. from the centers of piers and carried 4-in. spandrel walls; there were 1,000 cu. yds. of concrete in the arches and 600 cu. yds. in the piers. Each arch ring was reinforced by a grillage of longitudinal and transverse rods.
Fig. 159.—End View of Center for Short Elliptical Arch Spans.
Forms and Centers.—Figure 159 is an end view of the center arch. It consists of a series of bents, 6 ft. c. to c., the posts of each bent being 5 ft. c. to c. These posts are made of 2×6-in. Washington fir. Upon the heads of the posts rest 2×6-in. stringers, extending from bent to bent. Resting on these stringers are wooden blocks, or wedges, which support a series of cross-stringers, also of 2×6-in. stuff, spaced 2 ft. c. to c. On top of these cross-stringers rest the sheeting planks, which are 1×6-in. stuff, dressed on the upper side, and bent to the curve of the arch. This sheeting plank was not tongue and grooved, and a man standing under it, after it is nailed in place, could see daylight through the cracks. It looked as if it would leak like a sieve, and let much of the wet concrete mortar flow through the cracks, but, as a matter of fact, scarcely any escapes. Figure 160 shows a front view of a bent, and indicates the manner of sway bracing it with 1×4-in. stuff. Figure 161 shows the outer forms for the parapet wall, or concrete hand railing, and it will be noted that the cross-stringers are allowed to project about 3 ft. so as to furnish a place to fasten the braces which hold the upright studs. The inner forms for the parapet wall are shown in dotted lines. They are not put in place until all the concrete arch is built. Then they are erected and held to the outer forms by wire, and are sway braced to wooden cleats nailed to the top surface of the concrete arch.
