Gap elements in sol 101 behave just like linear springs. You need to use sol 106 for gaps to have the bilinear behavior.
You can also use the nonlinear elastic material trick for a rod in sol 106.
I tried to use the CGAP in SOL101 but I'm not able to get the behavior of a rope. I played hit the contact stiffness, etc. but no success. :confused:
@Jim: Is it possible to give me another tip.
Here's an example NX database with NX Nastran input decks and output files. There is a SOL 106 and SOL 101 version of the same model using CGAPS. Results are identical. Axial force in the cable/rope is zero in the compression subcase.