Solve X-Forces for Frame Statics Problem

In summary: The two x-components of that force are the forces on members BC and BD, respectively.In summary, you have solved for the Y forces, but are unsure of the X-forces. You are using the method of sections to solve for the X-forces, but are unsure of your value of Dx. There is a force acting on B that is due to the loads on members BC and BD.
  • #1
bob1352
6
1
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 postive 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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  • #2
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.
 
  • #3
So Bx, Cx and Dx should be zero then? I am not using the method of joints, but the technique for multi-force members.
 
  • #4
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?
 
  • #5
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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  • #6
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:

FAQ: Solve X-Forces for Frame Statics Problem

What is the first step in solving for X-forces in a frame statics problem?

The first step in solving for X-forces in a frame statics problem is to draw a detailed free-body diagram (FBD) of the entire structure. This diagram should include all applied loads, support reactions, and dimensions. Identifying all the forces acting on the frame is crucial for setting up the equilibrium equations.

How do you determine the support reactions in a frame statics problem?

To determine the support reactions, you need to apply the equilibrium equations to the entire frame. These equations include the sum of all horizontal forces equaling zero, the sum of all vertical forces equaling zero, and the sum of all moments about any point equaling zero. Solving these equations will give you the support reactions.

How can you identify zero-force members in a frame?

Zero-force members can often be identified using specific rules. For example, if two non-collinear members meet at a joint that has no external load or support, those members are zero-force members. Additionally, if three members form a truss joint and two of them are collinear, the third member is a zero-force member if no external load or support is applied at the joint.

What role do internal forces play in solving frame statics problems?

Internal forces are crucial for understanding how the frame carries the applied loads. To find internal forces, you often need to isolate a section of the frame and draw a free-body diagram for that section. This allows you to apply the equilibrium equations to solve for the internal forces in the members of the frame.

How do you handle complex frames with multiple members and joints?

For complex frames, the method of joints or the method of sections can be used. The method of joints involves isolating each joint and applying the equilibrium equations to solve for the forces in the connected members. The method of sections involves cutting the frame into sections and applying the equilibrium equations to solve for the forces in the cut members. In both methods, it's important to proceed systematically and check your work for consistency.

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