Page 178 - Water Engineering Hydraulics, Distribution and Treatment

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Water Hydraulics, Transmission, and Appurtenances
Chapter 5
EXAMPLE 5.51 PRESSURE INTENSITY AND FORCE OF PIPE’S MECHANICAL JOINTS
In jointed cast iron pipes, the longitudinal stresses can be resisted by the mechanical joints. Determine the pressure intensity and total
force resisted by the mechanical joints of a 24 in. (609.6 mm) bell-and-spigot cast iron pipe.
Solution 1 (US Customary System):
p = [3,800∕(d + 6)] − 40
= [3,800∕(24 + 6)] − 40
= 86.66 psig.
2
P = [3,000∕(d + 6) − 31]d
f
= [3,000∕(24 + 6) − 31](24) 2
= 39,744 lb.
Solution 2 (SI System):
p = [670,000∕(d + 152)] − 278
= [670,000∕(609.6 + 152)] − 278
= 601.73 kPa gauge.
P = [525∕(d + 152) − 0.2]d 2
f
= [525∕(609.6 + 152) − 0.2](609.6) 2
= 181,844 N.
Tables of standard dimensions and laying lengths are
found in professional manuals, specifications of the Ameri-
can Water Works Association (AWWA), and publications of
manufacturers and trade associations.
5.7 LOCATION
Supply conduits are located in much the same way as rail-
roads and highways.

5.7.1 Line and Grade
The invert of a grade aqueduct or grade tunnel is placed on the
same slope as the HGL. Cut and fill, as well as cut and cover,
are balanced to maintain a uniform gradient and reduce haul.
Valleys and rivers that would be bridged by railroads and
highways may be bridged also by aqueducts. Such indeed
was the practice of ancient Rome, but modern aqueducts no
longer rise above valley, stream, and hamlet except where a
bridge is needed primarily to carry road or railway traffic.
Pressure conduits have taken their place. Sometimes they
are laid in trenches as sag pipes to traverse valleys and pass
beneath streams; sometimes they strike deep below Earth’s
surface in pressure tunnels for which geologic exploration
fixes both line and grade.
Pressure aqueducts and pipelines move freely up and
down slopes. For economy they should hug the HGL in pro-
file and a straight line in plan (Fig. 5.23). The size and thick-
ness of conduit and difficulty of construction must be kept in Figure 5.23 Concrete water pipe (Source:
http://upload.wikimedia.org/wikipedia/commons/2/2e/Concrete_
balance with length. The shortest route is not necessarily the
water_pipe.jpg).
cheapest.