Missing DOFs when using CELAS/RIGID

Question I have a plate structure connected to a rigid frame using celas elements. Some of the frame nodes are free in space, why are they eliminated during assembly ?

Answer celas and rigid elements are used to create connections between physical nodes. They are thus ignored when creating the DOF definition vector of the model. To keep DOFs of nodes only connected to celas or rigid elements you must add concentrated masses mass1 elements at those nodes.