Hi @fethio,
I’m glad to be able to maybe contribute. From the documentation, I understand that there are two ways. But, as you mentioned, they are all a relative displacement between the split surfaces.
The first is to apply a constant force using Cload to the node using PRE-TENSION. For example:
Let’s say that the top is SSurface_from_nodes.
*PRE-TENSION SECTION, SURFACE=SSurface_from_nodes, NODE=Ref_Node
0., 0., -1.
…
*Cload
Ref_Node, 1, 490000.0
Secondly, apply a displacement with a fixed Boundary, using the previous step with op=MOD.
*PRE-TENSION SECTION, SURFACE=SSurface_from_nodes, NODE=Ref_Node
0., 0., -1.
…
*Boundary, op=MOD
*Boundary
Ref_Node, 3, 3, 0
I have used both. First, in the second step of my analysis, I applied force and displacement to simulate other loads applied to the structure. However, I’m still working on it to achieve better results.
This example was the best for me: Bolted Connections - #5 by JuanP74
Please let me know if this answers your question, and we can discuss finding a better solution.