Page 181 - Water Engineering Hydraulics, Distribution and Treatment

EXAMPLE 5.53 FREEZING INDEX AND FROST DEPTH REQUIREMENT IN NORTH AMERICA
In the absence of daily readings, the value of freezing index F may be approximated by Eqs. (5.42a) and (5.42b), using the US
customary units and the SI units, respectively. Determine the freezing index of a northern state in the United States assuming the
following coldest monthly temperatures recorded:
◦
◦
m
m
23
−5
−3.33
January
26
February
24
−4.44
−0.55
31
March
Solution 1 (US Customary System): December T ( F) T ( C) 5.8 Materials of Construction 159
ΣT = 23 + 26 + 24 + 31 = 104.
m
F = (32n −ΣT ) × 30.2
m
= (32 × 4 − 104) × 30.2
= 724.8.
d = 1.65F 0.468
= 1.65(724.8) 0.468
= 35.98 in.> 12 in. Select 36 in. of fill material.
Solution 2 (SI System):
ΣT =−5 − 3.33 − 4.44 − 0.55 =−13.32.
m
F = [0 −ΣT ] × 30.2
m
= [0 − (−13.32)] × 30.2
= 402.26.
d = 55.18F 0.468
= 55.18 (402.26) 0.468
= 913.46 mm > 305 mm. Select 1 m of fill material.
5.8 MATERIALS OF CONSTRUCTION Loss of capacity with age or, more strictly, with ser-
vice depends on the properties of the water carried and the
Selection of pipeline materials is based on carrying capacity,
characteristics of the pipe. Modern methods for controlling
strength, life or durability, ease of transportation, handling,
aggressive water promise that the corrosion of metallic pipes
and laying, safety, availability, cost in place, and cost of
and the disintegration of cement linings and of reinforced
maintenance. Various types of iron, steel, reinforced con-
concrete pipe will be held in check very largely, if not fully.
crete, and fiberglass are most used for water transmission
Cement and bituminous-enamel linings and reinforced
pipes, but plastic pipes are now being made in the smaller
concrete and fiberglass pipes do not, as a rule, deteriorate
sizes. Other materials may come into use in the future.
significantly with service.
5.8.1 Carrying Capacity 5.8.2 Strength
The initial value of the Hazen–Williams coefficient C hovers Steel pipes can resist high internal pressures, but large lines
around 140 for all types of well-laid pipelines but tends to be cannot withstand heavy external loads or partial vacuums
somewhat higher for reinforced concrete and fiberglass lines unless special measures are taken to resist these forces. Duc-
and to drop to a normal value of about 130 for unlined cast tile iron and fiberglass pipes are good for moderately high
iron pipe. Cast iron and steel pipes lined with cement or with water pressures and appreciable external loads, provided that
bituminous enamel possess coefficients of 130 and over on they are properly bedded. Prestressed reinforced concrete
the basis of their nominal diameter; improved smoothness pipe is satisfactory for high water pressures. All types of
offsets the reduction in cross-section. concrete pipe can be designed to support high external loads.