Underlying Theory - CAESAR II - Help

CAESAR II Users Guide

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The behavior of steel and other homogeneous materials has been long understood, permitting their widespread use as construction materials. The development of the piping and pressure vessel codes (Reference 1) in the early part of this century led to the confidence in their use in piping applications. The work of Markl and others in the 1940’s and 1950’s was responsible for the formalization of today’s pipe stress methods, leading to an ensuing diversification of piping codes on an industry by industry basis. The advent of the digital computer, and with it the appearance of the first pipe stress analysis software (Reference 2), further increased the confidence with which steel pipe could be used in critical applications. The 1980’s saw the wide spread proliferation of the microcomputer, with associated pipe stress analysis software, which in conjunction with training, technical support, and available literature, has brought stress analysis capability to almost all engineers. In short, an accumulated experience of close to 100 years, in conjunction with ever improving technology has led to the utmost confidence on the part of today’s engineers when specifying, designing, and analyzing steel, or other metallic, pipe.

For fiberglass reinforced plastic (FRP) and other composite piping materials, the situation is not the same. Fiberglass reinforced plastic was developed only as recently as the 1950’s, and did not come into wide spread use until a decade later (Reference 3). There is not a large base of stress analysis experience, although not from a lack of commitment on the part of FRP vendors. Most vendors conduct extensive stress testing on their components, including hydrostatic and cyclic pressure, uni-axial tensile and compressive, bending, and combined loading tests. The problem is due to the traditional difficulty associated with, and lack of understanding of, stress analysis of heterogeneous materials. First, the behavior and failure modes of these materials are highly complex and not fully understood, leading to inexact analytical methods and a general lack of agreement on the best course of action to follow. This lack of agreement has slowed the simplification and standardization of the analytical methods into universally recognized codes BS 7159 Code Design and Construction of Glass Reinforced Plastics Piping (GRP) Systems for Individual Plants or Sites and UKOOA Specification and Recommended Practice for the Use of GRP Piping Offshore being notable exceptions. Second, the heterogeneous, orthotropic behavior of FRP and other composite materials has hindered the use of the pipe stress analysis algorithms developed for homogeneous, isotropic materials associated with crystalline structures. A lack of generally accepted analytical procedures has contributed to a general reluctance to use FRP piping for critical applications.

Stress analysis of FRP components must be viewed on many levels. These levels, or scales, have been called Micro-Mini-Macro levels, with analysis proceeding along the levels according to the "MMM" principle (Reference 4).