The rules for the reinforcement of concrete pipe recommended in Volume XV, 1919, of the Transactions of the Concrete Institute are as follows:
No reinforcement is approved for pipe between 30 and 60 inches in diameter or in rock or hard soils. For pipe 36 inches in diameter or less the minimum thickness of shell shall be 5 inches. For 60–inch pipe the minimum thickness shall be 7 inches with intermediate sizes in proportion. Reinforcement for circular pipe shall consist of one or two rings of circular wire fabric or rods of the areas shown in Table 39. All sewers near the surface and subject to vibration should be reinforced. For sewers 6 feet or less in diameter the reinforcement should consist of at least ½ of 1 per cent of the area of the concrete. It should be placed near the inside at the crown and near the outside at the haunches. If large horizontal pressures are expected the pipe should be reinforced for these reverse stresses, which involves placing the reinforcement near the outside at the crown and near the inside at the haunches. The minimum thickness of the walls of sewers greater than 6 feet in diameter with flat bottom and arch, with or without side walls, should be 8 inches.
REINFORCEMENT FOR CIRCULAR CONCRETE SEWER PIPE
(See Vol. XV, Proceedings Am. Concrete Institute) ─────────────────┬─────────────────┬─────────────────┬───────────────── Diameter in │Minimum Thickness│ Number of Rings │ Cross Sectional Inches │ of Shell in │ │Area of Each Ring │ Inches │ │ ─────────────────┼─────────────────┼─────────────────┼───────────────── 24 │3 │1 │.058 27 │3 │1 │.068 30 │3½ │1 │.080 33 │4 │1 │.107 36 │4 │1 │.146 39 │4 │1 │.146 42 │4½ │1 │.153 48 │5 │2 │.107 54 │5½ │2 │.123 60 │6 │2 │.146 66 │6½ │2 │.168 72 │7 │2 │.180 84 │8 │2 │.208 96 │9 │2 │.245 ─────────────────┴─────────────────┴─────────────────┴─────────────────
Three methods for the reinforcement of concrete sewers are shown in Fig. 76 B.
=93. Proportioning of Concrete.=—In the proportioning of concrete questions of strength, of permeability, and of workability[54] may need consideration. All of these qualities are affected by the amount of cement, the nature and gradation and relative proportions of the fine and the coarse aggregate, and the amount of mixing water used.