RBE3 Issue

[Jon]

I came across and issue with the RBE3 element. I have already emailed Bill about the issue, but I thought I would post here for the benefit of the rest pf the community.

I am using a RBE3 to distribute load at a bolted joint. The joint is in thin sheet metal structure so I do not want the fasteners to take out of plane load. I used the following RBE3 to accomplish this.

RBE3          17              17  123456   0.189      13    9901   0.189+     
+             13    9902   0.189      13    9903   0.189      13    9904+     
+          0.189      12    9905   0.189      12    9906   0.189      12+     
+           9907   0.189      12    9908   0.189      12    9909   0.189+     
+             12    9910   0.189      12    9911   0.189      12    9912+     
+          0.189      13    9913   0.189      13    9914   0.189      13+     
+           9915   0.189      13    9916

When I run this through MYSTRAN the SPC forces are not equal and opposite the applied loads. The SPC forces in the Y and Z directions are half of what they should be.  It appears that the RBE3 is incorrectly calculating the weighted average when one or more independent nodes are not effective in all three translational DOF. To check this I changed the RBE3 to have Ci = 123 for every independent node. I also ran my original model through NXNASTRAN. In both cases the SPC forces were equal and opposite to the applied loads.

I have attached copies of the BDF and F06 files for the original run and the run with Ci = 123.

Cheers.

Jon