Dear members

Can someone please advise if we can conduct pipe stress analysis for U/G plastic pipe (PE100)by using CAESAR? For above ground plastic, you may do it by creating new material in Caesar database.

Regards

Please be careful when doing pipe stress analysis for thermoplastic piping. This material has different short and long term behaviour, has large displacements when used above ground (not correctly in the 3D beam equations), and buried the biggest problem will be local buckling.

Thanks Corne,

Have you done UG plastic pipe stress using CAESAR or other stress package before? When you said local buckling is the biggest problem, how can we address this issue during the analysis?

Regards
STC

I have used CAESAR II for it before, but CAESAR II will only give you stresses due to internal pressure and bending. And as said before the bending will be calculated wrong due to the used 3D beam elements. This is no problem for small displacements, but for large displacements (as you normally have using thermoplastic piping) it will yield incorrect results.

CAESAR II can't address local buckling. It can't for steel and it can't for (thermo)plastic piping. You can use different methods to determine maximum allowable external/soil pressure. You can check for example the AWWA manuals.

Hello Corne,

I believe that the assumptions used in 3D beam element theory are for small displacements only, that is the initial lenght of the member is considered the same as the final length (L), as far as I've read in some matrix analysis books..Correct me if I'm wrong with my statement fellows. Just being curious if there are commercial software that addresses this issue (such as FEA programs)?....

Many thanks in advance,

The problem is not that the final length = initial length. The problem is that the intitial dx = final dx.
Let's assume a pipe with the following 2 nodes: 0,0,0 and 2000,0,0 (in mm).
If we move the end node 50mm, the length changes as the new coordinate becomes 2000,0,50. This is tricky for large displacements like you have with thermoplastic piping and sometimes also with bellows.

CAESAR II is a FE(A) program. The finite element used is the 3D beam element. If you would model the piping in 3D solid elements (using a real solid model) this problem will not occur. However this is tedious and you don't have the stress check which CAESAR II does.

Thanks Corne for that clarification...

Dear STC,
I am also strugling for PE 100 buried stress analysis.The calculation by Caesar is giving abrupt reults
.If you had some model done for it then please email me at danishpetro@gmail.com

Ok MDA, I will forward PE100 UG model to you. The result looks quite a good.

Hi STC, Forward to me also. chkkra@gmail.com