fem coupling of elements with different dofs (beam and membrane)

[Vitto3]

i am working on a structural simulation of a windsurf sail. I have now to put in the membrane structure some beams, to keep it in shape (i am creating the code on my own).
Now, membrane elements have 3 degrees of freedom, while beam elements have 6. Membrane and beams are allready implemented separately.

But how can i do the coupling in the main rigidity matrix, if beam have 6 dofs and membrane elements have just 3? Do i need some interface conditions?

Hope you can help me, thanks

 

[rb1957]

i believe you can have membrane elements and plate elements sharing common nodes, and that the plate will have zero moment at the boundary.

 

[Vitto3]

Yes, they are sharing the same nodes, but it is membrane and beam (not plate!) elements. So you mean i could give the membrane 6 dofs and see it like a plate with no bending moments? And i can just sum the stiffness matrix of membrane with the one of the beams to get the final stiffness matrix?

 

[rb1957]

ok, you have a structure of beams and either membranes (thin webs) or plates (thick wbes) between them ... either model should work, so it'd depend on reality ... are the webs thick or thin ?

 

[Vitto3]

They are thin! But you think if i sum the two stiffness matrixes, the one for membrane elements and the one for beam elements, then i allready have the final global stiffness matrix?