Anxious?
A flexible restraint should work. A bilinear restraint would seem to work the best but CAESAR II would not offer such bilinear response in a dynamic analysis - low initial stiffness, high stiffness after traveling a given amount. (CAESAR II only provides linear dynamic modeling.)
I would say if you are expecting travel beyond the no load point in a dynamic analysis, just include the higher stiffness at the outer limits of travel.
Perhaps a gapped restraint - zero restraint until a certain distance, then the wire stiffness.
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Dave Diehl