Free-Body Diagram at Flange B  
scene 3 of 14
The figure shows the free body diagram around flange B. The free body diagram cuts through members 1 and 2. The load on the flange is P which equals 110 kilo newtons directed vertically downwards. The reaction force on member 1 is F subscript 1 directed vertically upwards. The reaction force on member 2 is F subscript 2 directed vertically downwards.

To solve this problem, first consider equilibrium. Draw a free-body diagram around flange B.

Assume that the internal force in member (1) is tension.

The internal force in member (2) will also be assumed to be tension.

We will make this assumption even though we expect that the internal force in the post is actually compression. These types of problems are easier to work if we follow a consistent procedure.