Equilibrium  
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The figure shows the free body diagram of the L shaped rigid bar A B C D with a horizontal segment A B C of length 750 millimeters and a vertical segment C D of height 300 millimeters. The bar is pinned at C and supported by vertical and horizontal rods labeled 1 and 2 of length 600 millimeters and 150 millimeters at A and D respectively. The other end of the support rods is pinned. The free body diagram cuts through the support rods 1 and 2. A load P which equals 80 kilo newtons directed vertically downwards acts at the point B which is 400 millimeters to the right of C. The reaction force in support rod 1 is F subscript 1 directed vertically upwards and the reaction force in support rod 2 is F subscript 2 directed horizontally to the left.

Begin the solution by considering equilibrium. Draw a free-body diagram of rigid bar ABCD and write an equilibrium equation for ∑MC.

Assume tension forces act in members (1) and (2).

Even though it seems certain that F2 will actually be a compression force, we will assume that F2 is a tension force. This assumption will be made to maintain a consistent sign convention with the force-deformation relationships for axial members.

∑MC=F1(750 mm)-F2(300 mm)-P(400 mm)=0