I have the solution manual but I need to find out how did they get the forces fo

Question

I have the solution manual but I need to find out how did they get the forces for at point C and the moment.

The stair tread of the escalator is supported on two
of its sides by the moving pin at A and the roller at B. If a
man having a weight of 300 lb stands in the center of the
tread, determine the principal stresses developed in the
supporting truck on the cross section at point C. The stairs
move at constant velocity.

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Explanation / Answer

To get forces at C

Step 1: Draw FBD of the stair tread and find the vertical and horizontal forces at A and a vertical force at B. by balancing vertical, horizontal forces and moments about B.

Step 2:Then take the stair and separate the stair into 2 parts at C,i.e., AC and BC.

Step 3: Now draw the FBD of either AC or BC by placing vertical and horizontal forces F1, F2 at C and a moment M at C. Now find this force by balancing forces and moments. This will give you the desired answer.

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