Question about Statics problems involving frames

In summary: If you 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 ?You only need to take the couple for the member it works on.
  • #1
Yossi33
22
3
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
 
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  • #2
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?
 
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  • #3
question 8.png
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?
 
  • #4
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

:cool:
 
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  • #5
Lnewqban said:
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.
 

FAQ: Question about Statics problems involving frames

1. What is the difference between a frame and a truss in statics problems?

A frame is a structure composed of connected members that can resist external forces and moments, while a truss is a structure composed of connected members that can resist only axial forces. In other words, frames can resist both forces and moments, while trusses can only resist forces along their members.

2. How do I determine the reactions at the supports in a frame?

To determine the reactions at the supports in a frame, you can use the equations of static equilibrium. These equations state that the sum of all forces and moments acting on a body must equal zero. By applying these equations to the frame, you can solve for the reactions at the supports.

3. Can I assume all members in a frame are weightless?

No, in most statics problems involving frames, the weight of the members is considered in the calculations. However, in some cases, the weight of the members may be negligible and can be ignored.

4. How do I determine the internal forces in the members of a frame?

To determine the internal forces in the members of a frame, you can use the method of sections or the method of joints. These methods involve cutting the frame into smaller sections and analyzing the forces acting on each section to determine the internal forces in the members.

5. What are the most common assumptions made in statics problems involving frames?

The most common assumptions made in statics problems involving frames are that the members are connected by ideal pins or hinges, and that the members are in a state of static equilibrium. Additionally, the weight of the members may also be assumed to be negligible in some cases.

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