I wish to use some of my members (mainly frame) as pin-jointed (It will sustain only axial force) in my 3D structure and some of them as 3D beam element. For 3D beam there is no any additional modification required, simply using the bar element in RSA is enough for that purpose ,but to use or converts some members to behave like pin-jointed I need to define the member end releases e.g. first end Rx1=R1y=Rz1=released, second end Ry2=Rz2=released in local axes on the intended elements.
That means on pin jointed elements I should never observe end moments acting on the element ends. To implement that I choose aimed elements and apply the releases but I receive Instability Type 2 error. What could be the reason of that ?