# Bolt preloads in solution combinations

I have a question about using bolt preloads and solution combinations. If I have the same bolted joints and preloads in each base case in my solution combination, won't that compound forces and stresses in the bolted joints? For example if I have two base cases (that each contain the same bolt preloads) in my solution combination would my bolt tension and clamp force double in the solution combination results? Would it be more accurate to have the bolt preloads in only one of the base cases? Or maybe add a base case that is just the bolt preloads and remove them from the other base cases?

This is my first experience with ANSYS after using different FEA software and I'm still trying to figure it out.

Thank you.

Eric

## Comments

@ericmergen

Solution combinations are a great way to efficiently evaluate a large number of load cases without having to run a large number of solutions for a linear analysis.

Results are combined, such as stress, strain or displacement. Forces are inputs to the model, not results, so they are in the base cases.

Bolt Preload is a nonlinear analysis, so you are correct that if you combine two bolt preload solutions, the stress at the bolt will double.

I have seen it take hours to compute the bolt preload in step one, but only minutes to compute the solution to the force applied in step two. If you have the same bolt pretension but many different forces to apply, solving each of those nonlinear models from the beginning is a waste of time. By using a restart file that is saved at the end of step one, you can save hours when multiple step twos are solved using the restart file.

https://forum.ansys.com/discussion/7038/multiple-loads-restarted-from-initial-loadstep