CalculiX doesn’t have pipe elements. What’s more, its beam elements don’t use true beam finite element formulation - they are internally expanded to solid elements. Thus, likely the easiest way would be to model the structure with shell elements.
ah, i forgot to point out the capabilities of beam element faces were previously succeed in contact analysis. thanks for remembering
but eight integration points may not enough for internal/external pressure of pipe. also, i’m thinking in a different ways, seeking the possibilities using composed approach.
1D classical beam element formulation has many limitation and assumptions made. even for simple case of linear static, still questioned for curved and tapered members.
expanded beam element seems to try break the limit over classical beams. took the advantages of all nonlinearity (material, geometry and boundary) so it can be capable to do perform plasticity, contact and stability analysis.
it’s fairly common, number of equation become large and consequently in computational times of the user must concern for all these advancement.
Not much experience here, but I would start with downloading the codebase and looking for the routines used for expanding 1D and 2D elements into 3D. You must trace those and the corresponding lines in the main ccx file. Also, I would look into the provided 1D beam as a user element so you can see what it needs to be functional.
I too am interested. It would be nice if Calculix had true pipe elements. I see you already mentioned that Code Aster has both the tangent and elbow/bend elements. Ansys has pipe elements. I think (but am not sure) that Nastran has both elements. Stardyne had both and of course the old code SAP-IV had both. The source code for SAP-IV is still floating around (it’s written in Fortran).
One of the critical things about the bend element is that ovaling should be taken into account.