Determine force on each bolt due to water pressure

[DerekZ10]

Homework Statement

Homework Equations

Here is the problem and solution to the problem:

I don't understand how it is finding the forces on the bolts when it takes ƩMcd. What is going on there? I also don't see how sin(45) is coming into play.

Is there a different/better way to approach this problem? I seem to have a better way on the tip of my brain but just can't think of it.

Thank you.

 

[SteamKing]

1. The bolt circle radius is 0.32m. The distance of the upper or lower pair of bolts is 0.32 sin 45 from the center of the cover plate.
2. The FBD of the cover plate is taking its moment reference about the lower pair of bolts. The cover plate is idealized as a beam which is supported at the upper and lower bolt pairs. In essence, solving for the reactions of this idealized beam gives the forces on each pair of bolts when the hydrostatic head is applied to the cover plate.