Need help with mechanical property of GRP

Dear all,

Thank you for your help in advance.

We have been involved with a waste water control project and the client would like all the piping to be GRP. I have looked around and read a bit on GRP piping using ASTM D2996 and to determine the thickness you need to know allowable stress of GRP. From my understanding is that different layers composition will give different mechanical property. I am just wondering what is the method to determine these properties. Is there a way for me to calculate this instead of making all the thickness combination and send it for testing? I am very new to GRP any help or suggesting will be very much appreciated. Also if anyone have some guideline on long term hydro static test please give me some advice.