Hello Eric,

Solution Combinations add stress so if you have three models with Bolt Pretension, then you are getting three stresses added near the bolts.

Solution Combinations are best used on strictly linear analyses.

If the bolts were modeled as beams, try using a Fixed Joint to replace each beam.

If the bolts were modeld as solids, try using Bonded Contact only to joint the bolts to the holes.

Then all other loads will add together correctly in Solution Combination.