Shumard, Fisher, Rahman
Joining # 2006 Washington DC
Previous examinations of stresses in gasketed bell- and-spigot PVC pipe joints in North America have been limited to theoretical analyses and finite element evaluations, with the results relying on basic assumptions and observations. The objective of this study is to provide an accurate picture of the relative magnitude and locations of strains in the pipe joint in order to develop a better understanding of the affects of different installation variables. This picture is developed through the application of birefringent, photoelastic coating to pipe bells and spigots. The coating allows the actual strains to be “seen” as the observed fringe patterns change with applied stresses. Photoelastic strain evaluation has been used successfully by engineers as a strain measurement technique for many years. This study examines the strains imposed on a PVC bell-and-spigot joint with and without internal pressure. Several installation variables are examined : assembly with proper insertion and alignment, improper assembly by over- insertion, assembly with an axial offset, and a pipe bell with a ring deflection. The results are presented in two ways. The first is visually to provide the reader with a true picture of the strains in a bell-and-spigot joint. The second is with calibrated stress calculations to provide an idea of the magnitude of stresses in the properly and improperly assembled joints. Field scenarios that result in an improper joint are discussed, correct installation procedures are reviewed, and construction aids that help make a proper joint more quickly are presented.