Equilibrium  
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The figure shows the free body diagram around joint C. The free body diagram cuts through the column at the point below joint C which is marked 1. The forces on either side of joint C have a magnitude of 125 kilo newtons and are directed downwards. The force F subscript 1 acts vertically downwards along the column at point 1.

Draw a free-body diagram (FBD) that cuts through member (1) and includes the free end of the column. A positive internal axial force will be assumed.

Write the equilibrium equation for the sum of forces in the vertical (x) direction:

∑Fx=-2(125 kN)-F1=0

Therefore, the internal force in member (1) is:

F1=-250 kN

Note: The negative sign indicates that the internal force is actually compression.