Hello,

You can try using custom material in Caesar II using the data from HDPE vendor such as Elastic modulus (short term & long term?),poisson's ratio, expansion rate, density, etc. The only question will be establishing the allowable stress and Code to use. You can follow maybe the link you've provided regarding setting up the Code Allowable. I haven't read in detail the contents of the article but fundamentally Caesar II can also calculate beam stresses same as the all other beam type analysis software is doing. Maybe you can post process in excel the output from Caesar II and set-up your allowables. Anyway, this is just my general thought. It takes some man-hour to study and set-up this type of analysis.

Please correct if I have made any wrong statement.

Cheers!!