Hi,

I use Caesar II for quite a long time now, but never analyze a GRP pipe. Last week I try a GRP pipe for the first time, the code used is UKOOA. In the Configuration set-up the WAVIN55 manufacturer database is selected. The vendor (FPI) has provided me with the allowable and all the required factors. Everything is filled in correctly. The GRP pipe is 52", filled with water, internal pressure is 2 barg, temperature 50 C, and total pipe length is 330 m. with a resting support at every 10 m. I have calculated for two cases. Case 1 : Only one end is fixed. Case 2 : Both ends are fixed (with the intension to find out the required expansion loop). It is obvious that the stresses in case 1 are Ok, the thermal displacement of the free end is approx. 250 mm. It surprises me that in case 2 the stresses are Ok and no lateral movements of the pipe at the resting supports at all. This does not make any sense.
Can somebody tell me how to deal with this “problem” and what else needs to be checked (buckling ?).
Thanks and regards,

CAESAR II (like all pipe stress programs) uses the "3D Beam Element" when performing the flexibility analysis. The flexibility analysis assumes that overall system behavior is dominated by bending. Additionally, 2nd order effects (such as buckling) are not considered.

If your model is a straight run of pipe between two anchors, you won't get lateral displacement from your flexibility analysis, since this is a 2nd order effect.

Buckling can be a typical problem in GRP pipes ( another case is with Jacketted pipes ) where use of two axial stops on the same stretch is common because of low modulus of elasticity of these materials.You have to do a manual calculation only and check against Euler's first critical load.
BS7159 considers that the axial compressive stress due to two point fixity and the resulting circumferential tensile strain due to poisson effect has to be added to the circumferential strain due to pressure and checked against the allowable strain.

Regards