What is the role of Q and the source of moments in eccentric loading problems?

[morpheus343]

Homework Statement

Stresses at a point in the crossection due to an axial load in the centroid.

Relevant Equations

Swain formula

If there is an axial load on G the centroid and i want to calculate the stresses at point B , I will calculate the moments at point B then use the stress formula. I am confused as to what y and z is in this case. I know that y and z are the coordinates of the point that i want to calculate the stress at. Is it the same as zB and yB?

 

[Lnewqban]

How is the section anchored or restricted from movement induced by that axial force along the x axis?
What is Q representing?
What is the source of those moments?

 

[morpheus343]

How is the section anchored or restricted from movement induced by that axial force along the x axis?
What is Q representing?
What is the source of those moments?

For some reason i thought it's an eccentric loading problem but it's just σx=My*z/Iy due to P. Q axial force should not produce bending stresses only normal at point B of crossection.