U1 Beam Examples and documentation

Does anyone have some examples of using a U1 user beam element? The documentation on the U1 seems very sparse.

In particular, does the U1 work with different ways of specifying the beam orientation? Can orientation be specified on a per-element basis with the NORMAL definition?

What are the tradeoffs of using a U1 vs. a B32? My understanding is that B32 expands to a bunch of solid elements approximating the beam while U1 uses beam theory to provide the element stiffness matrix.

My inclination is to prefer U1 – am I missing something?

There is a userbeam.inp file in test examples package. When it comes to orientation of this element, there were 2 bugs related to it:

The second one is fixed but the first one still persists in the current version of CalculiX. It should be fixed in the next version though.

U1 element is meant to be used when beam has to be defined with section other than a few predefined ones.

Thanks for the response - and for the links to some discussion using U1 elements.

If I was using a simple beam section (say a rectangle) supported by CalculiX, what would be the expected differences of using the built-in B32R with RECTANGLE section vs. a U1 with GENERAL section?

The documentation only describes this element as a 3D Timoshenko beam element (for static linear elastic calculations and small deformations). There’s also a reference to the paper with the formulation of this element and some details regarding keyword syntax. It would be best to run some tests with this element having the same properties as an equivalent B31 element.

Here you can find some comparisons: CalculiX-Examples/Test/BeamSections at c6b5cc68fc5e868afe04ee312763779cad9302ef · calculix/CalculiX-Examples · GitHub