I have a project with several large (30-48") frp ducts running between FRP Flash Tanks and 316 SS condensers. THE FRP supplier waited over a year before informing us that the nozzle loads where too high. So we need to use bellows type expansion joints at the nozzles.

I'm using CII Ver 5.30.03 Build 120131. I read up on using the expansion joints and stuck in the axial, transverse, Torsional, and Effective ID values. However, if I look at the differential movement occuring across the joint, the restraint forces reported are 3 to 4 times higher then what (I think) they should be (mainly delta * stiffness).

BTW, the tanks and nozzles are modeled. I'm wondering if I can model the exp. joint using a cnode with restaints and displacements.

Am I missing something?

You should be VERY careful using an un-restrained expansion joint with FRP. FRP pipe is not a homogenous material but rather strains of fiberglass woven together in a criss-cross pattern. As such it requires the longitudinal pressure thrust to resist the hoop stress in the pipe. When you use an un-restrained expansion joint, it eliminates the longitudinal pressure thrust which has been known to cause the FRP to bubble and un-wrap.
I also suspect that the excessive loads you are talking about is the result of an unrestrained expansion joint and pressure thrust. I’ve attached a bulletin discussing pressure thrust which discusses this topic in depth. I’d recommend that you use a restrained expansion joint.

Thanks Dan, I'm looking at your attachment and other sources pertaining to EJs and FRP.