Do tensile and compressive stresses create moments?

Question

Below are 3 examples I designed. My question is about the tensile and compressive stresses that occur in 3 examples under the influence of a horizontal force F=100N (earthquake force). I ask my questions on examples:

1. I showed the forces and moments acting on the columns in the frame consisting of beams and columns. Here, the moment occurring in the columns is;

($f_{tensile},f_{pressure}\neq 0$)

$100Nm >Mo_{1}+Mo_{2}$

2. I showed an example of a curtain wall here. In the example here;

($f_{tensile},f_{pressure}\neq 0$)

$300Nm >M_{o}$

If the tensile and pressure forces are large enough in these two examples, can the moment occurring at the column or wall base be equal to $0$ ?

1. In the last example, I showed this. If the resulting tensile and compressive stresses create a moment, how is the balance of the object achieved ?

$Mo_{(tensile-pressure)}+Mo_{(action)}\neq Mo_{(reaction)}$

Here, the first moment is the moment coming from the tensile and pressure forces, the second moment is the moment coming from the $100N$ force, and the third moment is the reaction moment coming from the action-reaction principle.

Answer 1

All forces opposed by forces not in an opposite vector create moments. By opposite I mean any two vectors that cannot be combined into a single vector, which generally means parallel and opposite.

It's bot hard, any forces which would make the structure rotate or twist generate a moment. Pretty much any time the force doesn't pass through the center of the object. Only if a force opposes it as an exact opposite vector will it not create a moment.

In your diagrams, every force opposed by a force on the same axis is creating a moment.

Answer 2

For your second and third examples, no, the moments cannot vanish. This is because there is not a force and a moment, that's a simplification that does not apply in those cases. In those cases a better model is as follows (pardon the simplicity of the diagram)

The wall and the cantilever beam will have the stress distributions shown below on the supports. Then, the integration of those stresses (by the corresponding distances) will yield the moments that counteract the moment applied by the forces.

What you model as $f_{tensile}$ and $f_{compression}$ are the integrals of the positive and negative parts of the stress distribution, which is ignoring part of the actual support reaction and are not, in the strict physical sense, real.

For the first model, since the columns are modeled as a 1D element, you get the right force and moment model, but if you modeled them as you did the wall, you'd get the same inconsistency.

Hope this is clear enough, if not, let me know and I'll edit the answer.