Dear Friends
I'm working on SSI effects on the performance of 2D RC frames. the frame is modeled by means of elasticBC elements. Winkler approach is employed in the definition of SSI .soil springs are introduced to the model with zerolength elements in the vertical direction (a strip footing is also included using beamcolumn elements). a new Gap material is used for these springs. the question lies in the modal analysis.
period of the 1st mode of the structure is a very large number of order 10000-100000!!! I think this is because the 1st mode has been changed to "rocking". (the other modes have quite well periods)
but as well, I can find reports that have used springs and they don't seem to have the same problem.
[b]can anyone help?! are there any special conditions that I should assign to the zerolength springs or does the material used for the springs make such an error?[/b]
Thanks in advance
Large Fundamental Period when SSI is considered
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