How to calculate the axial force of structural mechanics

1. Axial force --- the pressure is negative and the tension is positive
shear force --- make the rod section rotate clockwise around any point in its body to be positive

2. The first figure fncd is obtained by adding the projection forces of two triangles. The negative sign in front of the formula indicates that the direction of the force is opposite to that shown in the figure
in the second picture, the projection forces of two triangles are added, but the two forces have opposite directions, one positive and one negative, and a negative sign is added in front of the bracket, so the symbols of the two forces are different.

4. Except for the zero pole, it can be calculated by the node method. If the detailed process is not needed, it can be directly calculated by the structural mechanics calculator

5. First calculate the reaction force of the basic support, and then (remove the support) analyze the structure with the thinking of analyzing the geometric invariant system - the middle hinge point and the middle chain link form an invariant system that conforms to the principle of two rigid plates, so you can take the moment of the middle hinge point.

6. This can be solved by the displacement method in structural mechanics. The process is certainly not detailed here. I can refer to the displacement method in Chapter 7 of structural mechanics by Longyu ball!

7.

There are only six nodes, how can you have eight nodes; There are node support only need two enough, you are adding four connecting rod. The sensory model is wrong

9. The answer to this question is: the unit of FA is n · m, which is the unit of bending moment. It's not equal to the unit of axial force.
My axial force is f