Handbook Plastic Pipe ring stiffness
Alternative Test Method for Thermoplastic Pipes
- General preface to importance of stiffness
The measurement of Pipe-stiffness is described in different national and international standars. The Ring-Stiffness of Pipes is one of the important indicators for the evaluation of Pipe stability.
But Ring-Stiffness should not be overvalued, always is has to be considered that the result are measured under Laboratory-conditions. The flexible behaviour of thermoplastic pipes is requested and it’s one of the reasons for the positive experience we made worldwide with thermoplastic pipes in the last 50 years.
it is important that pipes provide enough stiffness to avoid higher deformation than permitted and the wall structure provides enough structural stability to avoid local buckling. Thermoplastic pipes have the capability to avoid or at least to reduce stress concentrations due their flexibility. Yhe creep-behaviour under load is characteristic for thermoplastics and is very helpful to control the deflection-process, due the relaxation of stress-loaded areas.
Mostly the static designs are following international standards like AWWA M55 or the German DWA A 127, but un any case the procedure always considers the flexible behaviour of pipes and working with limits for maximal defermation (e.g. DWA A 127 : 6%)
The long-term experience shows clearly that the static calculations provide very realistic result and the pipe-deformation is lower than the calculated limit. The standards for Ring-Stiffness Test are concentrating on a defermation range of 3%, but also bigger larger deformations can be tested.