Solve X-Forces for Frame Statics Problem

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Discussion Overview

The discussion revolves around solving for the X-forces in a frame statics problem, following an initial calculation of Y forces. Participants explore various methods for analyzing the forces acting on the frame, including the method of sections and considerations of support types.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant presents their calculations for Y forces and initial attempts to solve for X forces, expressing uncertainty about their results.
  • Another participant notes that support A cannot take horizontal loads, indicating that this affects the analysis of forces at point B.
  • There is a suggestion that Bx, Cx, and Dx should be zero, with one participant indicating they are using the technique for multi-force members rather than the method of joints.
  • A later reply questions the reasoning behind the assertion that Bx, Cx, and Dx should be zero and requests a free body diagram (FBD) for clarification.
  • One participant critiques the calculation of Dx, stating that member DE should be treated as a beam supported at both ends and not as a cantilever beam, highlighting the implications of the support conditions on the analysis.

Areas of Agreement / Disagreement

Participants express differing views on the values of the X forces, with some suggesting they should be zero while others challenge this assertion. The discussion remains unresolved regarding the correct treatment of the forces and the calculations involved.

Contextual Notes

There are limitations regarding the assumptions made about the support types and the method of analysis used, which may affect the conclusions drawn about the forces in the frame.

bob1352
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Homework Statement
This is a weekly assignment problem.
Relevant Equations
Fnetx = 0
Fnety = 0
Sum of Moments at a point = 0
So for this problem I have already solved for the Y forces: Dy = 171.43 N, Cy = 228.57 N, and By = -428.57 N. For the X forces I split up the frame and took the moment of DE.

Me = 1.5(300) + 3.5(300) - 5(Dx), Dx = 300

For CD Dx = -Cx fo I got Cx = 300, as when you forces are two member Dx = -300 on member CD. Then I used the moment of ABC to solve for Bx

Ma = -2.5(Bx) + (5)300, Bx = 600 N.

I am almost positive my Y forces are correct, but I am unsure of the X-forces and I can balance the moments, but not the sum of the forces. Am I correct or am I missing something?
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Note that support A is of a type that is unable to take horizontal loads.
Link BD is working under compression, while link BE is working under tension.
Therefore, there are two x-component forces acting on B in opposite directions.
 
So Bx, Cx and Dx should be zero then? I am not using the method of joints, but the technique for multi-force members.
 
bob1352 said:
So Bx, Cx and Dx should be zero then?
What makes you to think that way?
bob1352 said:
I am not using the method of joints, but the technique for multi-force members.
Could you show us the FBD that you have done so far?
 
Lnewqban said:
What makes you to think that way?

Could you show us the FBD that you have done so far?
Sure, here you go. I split the frame into parts as what the method of sections suggests.
 

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bob1352 said:
Sure, here you go. I split the frame into parts as what the method of sections suggests.
Apologies about the delayed response.
Your work looks good, but your value of Dx is incorrect.
Member DE acts as a beam supported at both ends, not like a cantilever beam.
That is because pivot E can't provide any reactive moment.

Simultaneously, pin D is not free to rotate around pivot E under the two lateral loads.
A force must be preventing that rotation from happening.
That force reaches pin D via ground-member AB-pin B-member BD.

Frame Statics Problem (1).jpg
 

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Last edited:

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