Cast-Iron Pipe Culverts

Table 85 (page 575) shows that the average weight of the pipe per foot per square foot of waterway is about 70 pounds; and hence the cost of the trunk of a cast-iron pipe culvert, exclusive of trans portation and labor, is about 70 x 14 = $1.05 per lineal foot per sq. ft. of area. The cost of vitrified culvert pipes is, from Table 84 (page 574), about 30 cents per foot per square foot of waterway. The cost of the head walls required for vitrified and for cast-iron pipe culverts is substantially the same; and hence the above data show approximately the relative cost of the two forms of culvert. According to this showing, cast-iron is considerably more expensive than vitrified clay; but this difference is partly neutralized by the greater ease with which the iron pipe can be put into place either in new work or in replacing a wooden box culvert.

0oxoRETE

PIPE OULVERTS. Concrete pipes both plain and reinforced have been employed for culverts. Plain concrete is most suitable for small sizes, but it has been used for pipes 48 inches inside diameter. There are three reasons why plain concrete is less desirable for culvert pipe than reinforced concrete, viz.: 1. The plain concrete is heavier for the same strength, and hence is more to handle. 2. The plain concrete is more likely to be broken in handling. 3. Plain concrete is unable to stand any con siderable distortion of its cross section without collapse.

Plain Concrete Culvert Pipe.

Plain concrete culvert pipe are on the market. They have either square-butting or beveled telescoping joints. The latter are likely to crack on account of the unequal settlement of adjacent pipes. For a description of the forms and the dimensions of plain concrete culvert pipe, see Journal Western Society of Engineers, Vol. xii, p. 83-88:

Reinforced Concrete Culvert Pipe. Recently reinforced con crete pipe 2, 3, and 4 feet in inside diameter have been used by rail roads in culvert construction. The pipes usually have a bell and spigot joint; and have a hoop reinforcement which is near the interior surface at the top and bottom of the pipe, and near the exterior surface at the sides of the pipe. The 48-inch pipe is 4 inches thick, and the reinforcement consists of hoops spaced 3 inches center to center and longitudinal bars spaced 8 inches, both being finch square corrugated bars. The smaller pipes are reinforced with wife net. The pipes are made in 8-ft. lengths. Such pipe can be rolled from the cars on skids the sams as cast-iron pipe The strength of reinforced concerte pipe will vary with the amount of reinforcement and with the age of the concrete. Some tests made by bedding a 48-inch pipe in sand in a strong box and applying a load as nearly uniform as possible over the horizontal projection of the pipe, gave an average breaking load of 6,960 lb. pei sq. ft., for pipe about 180 days old and containing approximately 1 per cent of reinforcement.* The strength of a 48-inch cast-iron pipe 1.50 inches thick was 13,000 lb. per sq. ft.f This shows that the cast iron pipe is nearly twice as strong as the reinforced concrete. How ever, the strength of the concrete pipe could be materially increased at very little expense by adding a little concrete on the compression side at the top, bottom, and sides of the pipe. Under ordinary conditions, the 48-inch concrete pipe costs only about 60 per cent as much as the cast-iron and the 36-inch about 75 per cent; and for sizes less than 36 inches cast-iron pipe is more economical.