The use of U1 and B31 elements in one simulation causes an error

1

Hello,
I am trying to use U1 and B31 elements in simulation because I found U1 is useful when I connect beam to solid.

However if I add B31 element, even when when it is not connected to U1, the simulation makes error.
<*ERROR in gen3delem: first thickness
in node 1 of element 1
is zero>

Input file is
*NODE, NSET=Nall
1,0.,0.,0.
2,50.,0.,0.
3,0.,20.,0.
4,50.,20.,0.
*ELEMENT, TYPE=U1, ELSET=Eu1
1,1,2
*USER ELEMENT,TYPE=U1,NODES=2,INTEGRATION POINTS=2,MAXDOF=6
*ELEMENT, TYPE=B31, ELSET=Eb31
2,3,4
*MATERIAL,NAME=steel
*ELASTIC
200.e3,0.3
*BEAM SECTION,ELSET=Eu1,MATERIAL=steel,SECTION=GENERAL
314.000, 7854.000, 0, 7854.000, 0.866
0.,1.,0.
*BEAM SECTION,ELSET=Eb31,MATERIAL=steel,SECTION=Rect
20,20
0.,1.,0.
*STEP
*STATIC
*CLOAD
2,1,1.
4,1,1.
*END STEP

2

It seems that you can’t use U1 and regular beam elements in one analysis. I’m not really surprised since U1 are quite new and specific. CalculiX often doesn’t print precise error messages in such cases.