Is My Free Body Diagram for a Frame Accurate?

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SUMMARY

The discussion focuses on the accuracy of a Free Body Diagram (FBD) for a frame structure, specifically addressing the omission of force P and the location of point D. Participants emphasize the importance of understanding rigid bodies and internal moments, clarifying that FBDs only depict external forces. Key resources provided include Lumen Learning's chapters on drawing FBDs and static equilibrium, which are essential for grasping the fundamentals of mechanics.

PREREQUISITES
  • Understanding of Free Body Diagrams (FBD)
  • Knowledge of rigid body mechanics
  • Familiarity with static equilibrium concepts
  • Basic principles of forces and moments in structures
NEXT STEPS
  • Study the Lumen Learning chapter on drawing Free Body Diagrams
  • Review the Lumen Learning chapter on examples of static equilibrium
  • Learn about the three equations of balance for forces and moments
  • Examine the provided presentation on solid mechanics and reactions
USEFUL FOR

Students and professionals in engineering, particularly those studying mechanics, structural analysis, and anyone looking to improve their understanding of Free Body Diagrams and static equilibrium in frame structures.

YehiaMedhat
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Homework Statement
Can you check my free body diagrams for the whole frames
Relevant Equations
$\sum F_y=0,\sum F_x=0$
Screenshot_20221224-203634_Xodo Docs.jpg
can you check if I sketched it correctly?
And please if you know any good resources refrence it.
Screenshot_20221224-171241_Xodo Docs.jpg
 
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Welcome, @YehiaMedhat !

It seems to me that P is missing, as well as location of D.
Note that for the armature not to collapse, the L-shaped element BC must be rigid and resisting an internal moment.
 
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More explanation please.
And where could i find info i need for this?
 
YehiaMedhat said:
More explanation please.
The joint where B and C meet is the only rigid joint in the structure. Can you not see how the whole thing would just fold downwards against the wall if BC is not rigid?
 
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It seems that i don't even understand what rigid body means
 
YehiaMedhat said:
It seems that i don't even understand what rigid body means
It means a body for which none of the parts can move relative to each other. Only the whole body can move.
 
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Well I understand that but why there's an internal moment and where i should put on the sketch.
I'm sorry but all the mechanics is confusing so I try hard to gather informed together
 
YehiaMedhat said:
Well I understand that but why there's an internal moment and where i should put on the sketch.
I'm sorry but all the mechanics is confusing so I try hard to gather informed together
It seems to me that your problem here is that you don't understand the fundamentals of simple joints yet, so a problem this complex is beyond you. I recommend studying the basic more.
 
Can you refrence a specific object.
Cause I actually did revise from the text book and online tutorials about fbd and frames in general
 
  • #10
YehiaMedhat said:
Well I understand that but why there's an internal moment and where i should put on the sketch.
I'm sorry but all the mechanics is confusing so I try hard to gather informed together
Clarification:
You don't need to put any internal force on the sketch, as a FBD only shows external forces on each member.
That includes force P, which you have not shown.

Please, see:
https://courses.lumenlearning.com/suny-osuniversityphysics/chapter/5-7-drawing-free-body-diagrams/

and

https://courses.lumenlearning.com/s.../chapter/12-2-examples-of-static-equilibrium/

Sorry about the induced confusion.
I just tried to imply that the L=shaped member BC could be replaced with a straight string, rope or chain, without affecting the static balance of the armature.

eng130C4_t1-scaled.jpg
 
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  • #11
That's great. Thanks for help Mr. Lnewqban and Mr. Phindin
 
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  • #12
YehiaMedhat said:
That's great. Thanks for help Mr. Lnewqban and Mr. Phindin
You are welcome. :smile:

In these problems, the first step is to treat the armature as a solid regarding forces and reactions acting on it.
For that, you use the three equations of balance of x-forces, y-forces and moments that you know.

In that way, you can find the values of the reactions (at points A and B in this case).
You can then use those calculated values to solve the rest of the questions in the problem (forces at connections of links).

If interested, please see this presentation:
https://www.iitg.ac.in/rkbc/me101/Presentation/L-06-08.pdf

🎄:cool: 🎄
 
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  • #13
That's great.
👍
 
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