It’s usually done using 3 cylinder - shaft, head and nut. Then you don’t need BCs for the bolts themselves, you can apply pre-tension section and read the forces using the section print feature.
The details are shown here: https://youtu.be/ZSDf1bNXo8g?is=Fe6zNqbjPXzG4vdm
Check also this thread: Error during analysis of baseplate fixing