Solving stud Pretension in Optistruct solver

Suggestions:
* Friction or STICK can cause more difficult nonlinear convergence - if feasible
   try frictionless gap/contact.
   Or try stabilized version of expert system: PARAM,EXPERTNL,CNTSTB.
* This problem has gap elements with friction or stick condition. For more
   intuitive results and often better convergence, set GAPOFFS on GAPPRM card
   to AUTO. (This may violate rigid body balance, especially for unsupported
   structures.) * This problem has nonlinear materials and the number of load increments is small.
   Increasing NINC may help achieve convergence.

Also reading this might give you some extra tips:

https://community.altair.com/community?id=community_blog&sys_id=538764ab1b3790d4a5f742eddc4bcba4