Hello,
I can't seem to find a solution to my problem. I modeled a steel arch suspension bridge in Robot 2018 (see attached file). The hangers were modeled as bars. During calculations a warning about instability (type 3) appears, I believe due to the big difference in stiffness. As far as I know, this isn't a huge problem in static analysis (when I just want to find forces from applied loads), but I also want to perform a modal analysis in order to find the natural frenquencies of the whole structure. This causes an execution error 3060.
The instability changes its location from time to time, for example when I change the releases on all of the hangers. Maybe I should model the hangers as cables? I haven't used the cable function before, that's why I had chosen bars instead. I tried to change the releases, change modal parameters and apply the DSC algorithm - with no success. I've searched through the forum but did not find a problem similair enough to mine, to apply the solutions.
I really hope that someone will be able to help me. Any advice or help would be lifesaving for me.
Thank you in advance.
Attached file below
