I am doing a 3d soil structure interaction analysis so I started from the simplest case- everything is elastic. I used shell elements to simulate a surface foundation and used 'equalDOF' to tie the foundation nodes to the corresponding nodes on the surface of the soil domain (modeled using 'stdBrick').
The model worked for the static analysis where I applied forces to the foundation and could get reasonable responses. However, in the dynamic analysis where I applied horizontal force time history to the bottom nodes of the soil domain, I could get motions only for soil nodes. In the output files of the foundation nodes, only the time at each step appeared at the first column and there was no displacement history at all.
I also tried using 'elasticbeamcolumn' elements and 'rigiddiaphragm' to model the foundation but had the same problem. It seems that the foundation was isolated from the soil in the dynamic analysis even if I used 'equalDOF'' to connect them.
I defined my structure with a model builder of -ndm 3 -ndf 6 and my soil as -ndm 3 -ndf 3 with a stdbrick element. I connected the base of the structure with the brick elements with eqdof in dof1 and dof2. my analysis failed even for gravity load. what kind of constraints did you use to connect the base of the structure to the soil. Michael midezutd@gmail.com
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