Plastic Pipe Design # 2006 Washington DC
Plastics pipes products are more and more appreciated in sewer schemes throughout the world. The advantages of thermoplastics, like the good resistance against sewer environments and the possibility to built complete tight systems are many times the drivers to use thermoplastic pipes and chambers. Plastics chambers however are more complex then pipes. Where in solid wall pipes the structural performance is determined by two directions, in chambers this is threedimensional. Hence also the stresses and strains are of a more complex nature. The loading and loading condition is quite different for chambers when compared to pipes. Now three dimensional stress/strain conditions are present, and the product is placed vertically in the soil. ASTM F1759 (1) prescribes the loads and stresses on the manhole. Although the design rules are transparent and straightforward, they are of general nature and do not involve possibilities to calculate strains and stresses in the more complex chambers. It would be possible to use FE analysis for this purpose, but there are too many uncertainties and this kind of analysis might be useful for design, it is not for certification of the product. If the actual loading and functional performance of the chamber is used as the basis, then it is possible to design tests to check the integrity of the manhole or chamber. This approach has been followed in Europe and some of it has been reflected in drafting European standards. As an example the cover-load test, the ring stiffness test, shear load test, Base-buckling test and a durability test for the base are under development or have already been finalized. This paper shortly describes the tests and the results that are gained with it. It will also explain the importance of focussing on the functional performance of chambers.