ring stiffness of plastic pipes

[AgeOfEmpire]

Hi friends,

I am working in plastic pipe test lab. I try to explain my problem.
In spiral sewage plastic pipes, ring stiffness is most important parameter. According to the DIN 16961, elasticity modulus of HDPE at 24h (380MPa) and moment of inertia are used to determine ring stiffness value of HDPE by theoretical. Ring stiffness is also determined by parallel plate loading test method by experimentally. Elasticity modulus of HDPE at 24h is also used to calculate load quantity.
the problem is differences of these method. ring stiffness which determined by theoretically is different from the experimantal ring stiffness.

Is there any friend who have some experience as my problem.

Thank you for your interest.

 

[rconner]

I noticed you have gotten no response to your inquiry after many days. You might want to read the past threads at

http://eng-tips.com/viewthread.cfm?qid=224942

and

http://eng-tips.com/viewthread.cfm?qid=142221

that at least discuss some at least very short-term pipe stiffness testing and longer-term service aspects (beyond that I would only suspect there could additionally be some variations, localized stresses, and residual stress etc. in some profiled-walled pipes that might additionally render actual results not like "theoretical", particularly if the stresslevels are in a more inelastic range) .

 

[AgeOfEmpire]

Thank you for you attention rconner. I read these threads before but my problem is a litte different. According to the some articles, yes there is a difference between the therotical and experimental ring stiffness resuts but after pipe is burried. However, my problem occur before burried. It is so interesting. May be elasticity modulus or some stress which occur pipe is wraped reson for these results. I didn't find yet.