2D elements which are connected with RBE2 elements get a density of 0

Test123

Hello, everyone, 
I have a question regarding RBE2 elements.I wanted to compare RBE2 and RBE3 elements. You can see the model structure in figure 1. I wonder why the elements, which are connected to the RBE2 element, are assigned a density of 0 in the optimization result (figure 2) and whether this is a viewing error. 

 

Thanks in advance

<?xml version="1.0" encoding="UTF-8"?>

<?xml version="1.0" encoding="UTF-8"?>

tinh

Because they are rigid regardless density so OS chooses density 0 as minimum.

Actually you ought to move those elems to nondesign domain.