Hi Ranka,

I think that your instincts are correct. There will be compression, local membrane bending and shear all acting in the pipe wall at the point of contact with the support. Of course when we use beam theory (as does CAESAR 2) we calculate beam bending stresses over the gross section of the pipe. When you are using large diameter pipe (especially with heavy contents) this may not tell the whole story. You will have to look at these local (to the pipe wall) stresses as a combined stress using the most appropriate theory of failure (may I suggest Von Mises). Just remember, when you go away from B31 beam theory methods, it is no longer valid to use the B31 allowable stresses - you will want to look at the ASME Section VIII, Division 2 methodology and associated allowable stresses.

To properly analyze the local stresses in the unstiffened pipe wall you will need to take your CAESAR 2 calculated loads and use them in a finite element analysis (PIPE/FE, e.g.). The pipe will want to ovalize at the point of contact and a "doubler plate" might help the situation at the local contact point - but to truly understand the stress pattern around the ovalized section, you will need FEA.

You might look at how the folks that design penstocks support these big water pipe loads. They like to use ring stiffeners and support the pipe on columns that straddle the pipe. The ring stiffeners keep the pipe (somewhat) "round" at the point of support and the rings make convenient attachment points for hanger and supports (columns). If you can get a copy of AWWA Manual M11, you will see some manual methods for designing water pipe supports. There are also some manuals issued by the AISI that detail steel water pipe support schemes. I think the ring stiffener design methods for horizontal vessels are similar and these are described in the classic pressure equipment design book by Brownell and Young. Using these methods will preclude the need for FEA but they will provide a more conservative design margin ($$$).

You will probably end up having to design some steel base plates if you use short columns (for carrying the load to the ground) and you will find that you must also consider compression and bending on the plates (they want to "curl" under load - you will have to know how big the foundations are under the base plates). I think we all use the AISC Steel Design Manual method for designing base plates and anchor bolts. If you use this method, also use the allowable stresses given in the manual.

Good luck with your project.

Regards, John.