In the Mechanical app, on the Display tab, there is a slider on the Explode tool. Slide that over to visually separate the bolt from the concrete block and flange.  Please reply with that image and show what face was selected for Bolt Pretension.

In a Geometry editor, you should split the face of the shank of the bolt at a plane that is the flange thickness below the underside of the bolt head. That will provide a long face that will have bonded contact to hold the bolt into the concrete block and a short face that will have the bolt preload applied.