Page 295 - Buried Pipe Design

266 Chapter Five

Standards for prestressed concrete pressure pipe:
■ AWWA C301
■ AWWA C304

Design procedure
There are two basic steps in designing reinforced concrete pressure pipe.
1. Design the wall to resist the internal hydrostatic pressure acting
alone.
2. Determine the effect of external loads.
a. For AWWA C300– and AWWA C302–type pipes, use rigid pipe
concepts and a combined load analysis. In this analysis the wall
stresses, due to the internal pressure, are considered to be act-
ing simultaneously with the stresses produced by external
loads.
b. AWWA C303–type pipe is designed for external loads to control
both stresses and deflections. A combined loading analysis is not
required.

Design procedure for rigid pipe (AWWA
C300 and C302 types)
The rigid pipe design procedure involves the following steps:
1. Calculate the total circumferential steel area required to resist
internal pressure only, using the hoop tension equation for working
pressure and working pressure plus surge pressure.
2. For the selected wall thickness of AWWA C302–type pipe, calcu-
late the circumferential tensile stress in the concrete of the pipe wall
resulting from working pressure plus surge pressure. The concrete
strength or the wall thickness must be increased if the tensile stress
exceeds the allowable.
3. Calculate the pipe weight and water weight.
4. Calculate the external earth load on the pipe.
5. Calculate the external live load, if any, on the pipe. External dead
loads and live loads must be computed in accordance with recognized
and accepted theories, such as those presented in Chap. 2 of this book.
6. Calculate moments and thrusts for each load on the pipe, includ-
ing internal pressure. Values at the invert and at the side are required.
For normal loading conditions, the crown values do not control the
design.
The coefficients for moments and thrusts must be from recognized
and accepted theories, such as those presented by Paris (1921) and
Olander (1950). The bedding angle used in design must be compatible
with the installation criteria specified by the purchaser.