Behaviour of GRP Pipes under a Variety of Load Conditions

The equations governing the behaviour of circular cylindrical GRP pipes under a variety of loading conditions are derived. The pipes are assumed to be fabricated as a layered anisotropic system with through thickness symmetry. The well known Fourier expansion methods, used extensively in the analysis of isotropic shell problems by one of the authors, are extended to handle the more complex case of the anisotropic pipe.

In an effort to validate the approach with an existing solution, the general analysis is reduced to the specific case of the specially orthotropic lay up. Several ratios of E,/E. are considered when the pipe is loaded with a radial load applied over’a patch. Acceptable comparisons are obtained for values of E/E. that fall within normal pipe design.

Glass reinforced plastic cylinders are being increasingly used in both the process plant industries and in aircraft and space transportation. The lightness of the GRP product is of considerable value in the latter case where from 20% to 50% weight can be saved by the use of filament wound cylinders. The cylinders are subject to a variety of loading conditions depending upon their use.
For example, in the case of storage vessels, pressure vessels and pipes the cylinder is subject to internal pressure and fluid loading, plus, of course, the stressing caused by their support and other local attachment loading.

In designing these components it is clearly an advantage to make use of the fact that certain optimum conditions exist within the range of available parameters, e.g. an optimum filament winding angle @, or optimum ratios of elastic moduli, etc. In order to fully exploit these conditions it is necessary to derive the governing differential equations for the problem, devise a suitable method of solution and then carry out extensive parameter surveys. The work presented in this paper is a first step and after developing the governing equations seeks to confirm the validity of the approach. Later papers will present parameter surveys which will provide design information.