Contact pressure - screw pretension

Hello,
I'd like to calculate the max contact pressure in the below assembly, just before contact loss between the beam and the wall. The beam is clamped to the wall with a pretensioned screw, and sustaining a force at his gravity center.

I'm assuming all bodies dimensionnaly stable (no distorsion).

I wonder about few questions... how to calculate the maximum force at center of gravity before contact loss ? how to work out the composed pressure profile...

Here are some sketches that may help understanding the problem :

[IMG]http://www.engineersedge.com/engineering-forum/attachment.php?attachmentid=1689&stc=1[/IMG]

[IMG]http://www.engineersedge.com/engineering-forum/attachment.php?attachmentid=1690&stc=1[/IMG]

Thanks a lot for any kind of help.