Bending of bolt

This page should help you -

http://www.roymech.co.uk/Useful_Tables/Screws/Bolted_Joint.html

Note that in the example "Strength of bolt joints withstanding bending forces" that they did not analyze for the existing preload in the bolt. For example, a preloaded bolt that has a force of 100 lbs applied to it, does not necessarily 'see' an additional 100 lbs of force due to the stiffness of the joint. There is a page linked there that describes this phenomenon if you are not aware of it.

How does the bolt get bending stress? Please explain, with a sketch if possible.