Model Non linear spring (NLSPJJ) for Grouted connection

Hi, I am trying to model a non linear spring (using NLSPJJ) between two joints one one a leg member and the other on a pile member, considering that the anulus between the leg and pile is grouted. I am running a ship impact analysis using advanced collapse.

I have modelled the leg and pile as two separate members connected by wishbones and created two joints on the leg and pile at the same elevation.

I have the following doubts:

1. How to calculate the force deflection relation for the input in NLSPJJ card so as to stimulate the actual behaviour of a grouted concentric tubular leg and main pile.
2. What are the degrees of freedom i must consider to represent the grouted connection.

If a sample of the calculations and input lines is given it will be very much helpful. 

For reference I have pasted a pic of the collapse input file i am trying to create, below.

Thanks in Advance!