Where does a couple act when dismembering frames for FBDs?

[Yossi33]

Homework Statement

solving frames problems

Relevant Equations

couple of forces

hello, i have a question in this topic of frames in mechanic engineering, if i have a problem with 3 or 4 members that connected and a moment of couple is applied at specific frame,a moment of couple is general and is applied at any given point of the body. so when i dismember the frame and draw a free-body diagram of each member do i need take the couple in each member or just the member it works on ? thanks

 

[Lnewqban]

What type of frame are we discussing?
Is the moment co-planar with the frame?
How are the members connected to each other and to the ground?

 

[Yossi33]

for example in this problem a 3knm moment is applied at point G of CDE member and now if i dismember CBA and try to calculate moment in Z axis do i need to take this moment?

 

[Lnewqban]

Once a punctual moment is applied onto a member, any point of that member is under the influence of that moment.
Whether or not that influence is transferred to a neighbor member, depends on the capability of the point at which they meet to transfer torque; hence, the reason behind my third question.

A moment is just a concept; in the real world, you only have forces and levers.
Therefore, at the end of a member loaded with a "moment", you always have a force, which also implies a direction of application.

Please, see:
https://www.engineersedge.com/beam_bending/beam_bending35.htm

https://www.engineersedge.com/beam_bending/beam_bending51.htm

https://www.engineersedge.com/beam_bending/beam_bending51.htm

https://www.engineersedge.com/beam_bending/beam_bending55.htm

https://www.engineersedge.com/calculators/frame_deflections_concentrated_moment_14346.htm

https://www.engineersedge.com/calculators/frame_deflections_concentrated_moment_14346.htm

 

[haruspex]

in the real world, you only have forces and levers.

Sure, but in the diagram it is a twist around a vertical axis, so there is no shown lever to apply the force to.
I assume ABC and CDE are rigid elbows freely hinged to each other and to rod BD.