Equilibrium  
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The figure shows the free body diagram of the rigid bar A C B and the supporting rods. The free body diagram cuts through rods 1 and 2. The force along rods 1 and 2 are F subscript 1 and F subscript 2 directed vertically upwards. The force at the end point D of the support rod C D has a magnitude of 80 kilo newtons and is directed vertically downwards.

Begin by drawing a free-body diagram (FBD) that cuts through rods (1) and (2).

Write two equilibrium equations for this FBD:

∑Fy=F1+F2-80 kN=0

∑MA=(F2)(1.0 m)            -(80 kN)(0.7 m)=0

and solve for the internal forces in rods (1) and (2):

F1=24 kNF2=56 kN

By inspection, the internal force in rod (3) is:

F3=80 kN