TABLE OF CONTENTS The design methods for buried pressure pipe installations are some-what similar to the design methods for gravity pipe installations which were discussed in Chap. 3. There are two major differences:
Design for internal pressure must be included.
Pressure pipes are normally buried with less soil cover so the soil loads are usually less.
Included in this chapter are specific design techniques for various pressure piping products. Methods for determining internal loads, external loads, and combined loads are given along with design bases.
The stresses and resulting strains arise from various loadings. For buried pipes under pressure, these loadings are usually placed in two broad categories: internal pressure and external loads. The internal pressure is made up of the hydrostatic pressure and the surge pressure. The external loads are usually considered to be those caused by external soil pressure and/or surface (live) loads. Loads due to differential settlement, longitudinal bending, and shear loadings are also considered to be external loadings. Temperature-induced stresses may be considered to be caused by either internal or external effects.
Lam 's solution for stresses in a thick-walled circular cylinder is well known. For a circular cylinder loaded with internal pressure only, those stresses are as follows:
| where | P i | = internal pressure |
| a | = inside radius | |
| b | = outside radius | |
| r | = radius to point in question |
The maximum stress is the tangential stress ? t, and it occurs at r = a
