Externally Loaded RP Pipe

The use and acceptance of buried large-diameter glass fiber, plastic reinforced, filament-wound pipe has increased steadily since the 1950s. Such RP was selected for its superior corrosion-resistance characteristics and installation-cost savings. ASTM standards use the term Reinforced Thermoset Resin Pipe (RTRP). Filament-wound pipe with a double helical angle of continuous-glass reinforcement (discussed later) is but one of several types of RTR pipe constructions. 

Let us start by examining a rigid pipe. Because of its rigid, inflexible characteristics, surface load intensifies at the crown of a rigid pipe and is transmitted through the pipe directly to the bed of the trench in which the pipe rests. This is not true with flexible conduit. Because a flexible conduit deflects under covering load of earth, this deflection transfers portions of the load to the surrounding envelope of soil. This is true of both 

Steel and RTR pipe. The result is that the support of the surrounding earth actually increases the strength of the flexible conduit. Therefore, analyzing the type and consolidation of backfill materials must be considered an integral part of the design process. 

Given these differences between rigid and flexible conduit, let us look at the differences between steel and RTR pipe, both of which are, of course, flexible conduits. First, steel pipe is by definition constructed from a material, steel, that for our purposes is a homogeneous isotropic substance. Therefore, steel pipe can be considered to have the same material properties in all directions that is, it is equally strong in both the hoop and longitudinal directions (see Fig. 5-22). 

Broadly speaking, three factors control the physical properties of RTR pipe. These are the amount of continuous-glass filament used to construct the pipe wall, the prescribed 

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