The cross-section of the sewer is given by Fig. 261, which also shows the arrangement of the reinforcing bars. Johnson corrugated bars, old style, are used for reinforcement. The sections of the various reinforcing bars are: Longitudinal bars, 0.18 sq. in.; invert bars, 0.7 sq. in., and arch bars, 0.7 sq. in. The spacing of the bars and the arrangement of the splices are indicated on the drawings of Fig. 261. All splices have a lap of 36 ins. Some gravel concrete has been used in the invert, but most of the concrete has been crushed limestone and Mississippi River channel sand. The proportions were 1-3-6 in the invert and 1-2-5 in the arch. The arch was computed by Prof. Greene's method. The ultimate strength of concrete in compression was taken as 2,000 lbs. per sq. in. and the working strength at 500 lbs. per sq. in. The elastic limit of the reinforcing bars was taken at 50,000 lbs.
Fig. 261.—Harlem Creek Sewer, St. Louis, Mo.
The trenching was done by wheel scrapers to the amount of waste. Then a cableway was erected spanning the entire length of the section and the remainder of the material taken out. The last 4 or 5 ft. in depth were in limestone and the excavated rock was taken by cableway to dump carts which took it to the crusher and returned with crushed rock to be used for concrete. This rock foundation was taken advantage of to reduce the amount of invert concrete.
In constructing the sewer proper the invert was first concreted to template to the height shown in Fig. 262. The arch forms were then placed as shown in Fig. 262, and the roof arch concreted. Both templates and arch forms were constructed of wood. The arch forms were moved ahead on iron rails and jacked into place. The ribs were 2×10-in. pieces and were spaced 4 ft. on centers; the lagging was 2-in. tongue and grooved stuff and was smeared with crude oil. The reinforcing bars shown in Fig. 261 were bent to proper radius by means of a wagon tire bender and were held in place by templates. The concrete was all mixed by two Chicago Improved Cube mixers operated by electric power.
Fig. 262.—Center for Harlem Creek Sewer.
The cost records of constructing the section of 29-ft. sewer so far built are not susceptible of complete analysis, but the following figures can be given. The prices of materials were as follows:
| Cement, per barrel | $1.80 |
| Sand, per cubic yard | 0.75 |
| Broken stone, per cubic yard | 1.00 |
| Reinforcing bars, per pound | 0.02 |
| Vitrified brick, per 1,000 | 12.00 |
The wages paid different classes of labor were: