Analyzing Force Members and Trusses: Calculating Equilibrium and Moments

In summary, the student is trying to solve a problem in which they are not given a global coordinate system to work with. They are also using an internal force convention which may not be correct. They are then having trouble solving the equilibrium equations due to the indeterminate structure.
  • #1
jegues
1,097
3

Homework Statement



See Figure

Homework Equations



[tex] \sum F_{x} = 0 [/tex]
[tex] \sum F_{y} = 0 [/tex]
[tex] \sum M = 0 [/tex]

The Attempt at a Solution



See Figure

I'm fairly certain the force I drew at point D isn't at a 90 degree angle, but if its not I can't find the perpendicular distance for the horizontal/vertical distances at the point D.

This has been giving me a really big headache and a lot of stress lately so some help would be greatly appreciated!
 

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  • #2
* Use geometery to find length of members
* Then using method of joints, forces in the members can be easily found.
 
Last edited:
  • #3
I see you are using squared paper, but not drawing everything to scale. To do so would help you check the use of 3-4-5 triangles. Interestingly, these problems do not really depend on distances but on angles. If the units were km, the answer would be the same. This emphasises that the ratios of distances are the key to full understanding.
 
  • #4
Hey mate,

I am an applied mechanics tutor so I should be able to see you finish this problem under guidance. You are told to find the axial forces running through these members.

Step 1. Pick a set a global x-y coordinates to work with. This may be anywhere on the structure but for convenience I recommend doing so on the node A.

Step 2. Have yourself an internal force convention. This should be somewhere in your notes. i.e. tension positive, compression negative etc.

Step 3. Use the equilibrium equations you stated to find the reactions.

We now run into a problem here. You have two fixed supports. This structure is indeterminate by one degree. If indeterminate structures is what you are here for please reply back and confirm this so I may continue.

I have assumed you are new to solving statically determinate structures. Correct me if I am wrong.
 
  • #5
I understood FH to be a vertical link, so that F behaves like a roller support. That makes it stat det.
 

1. What is a 2 force member in a truss?

A 2 force member in a truss is a structural element that is only subjected to two forces acting in opposite directions along its length. This means that the member is either in tension or compression, and there are no additional forces acting on it.

2. How can we identify a 2 force member in a truss?

To identify a 2 force member in a truss, we can look for members that have only two connections and are not connected to any other members at their midpoint. Additionally, these members will have a force acting in one direction at one end and an equal force acting in the opposite direction at the other end.

3. Why is it important to consider 2 force members in truss analysis?

It is important to consider 2 force members in truss analysis because they have a significant impact on the overall stability and strength of the truss structure. Neglecting to account for these members can lead to inaccurate results and potentially compromise the safety of the structure.

4. Can a 2 force member be in equilibrium?

Yes, a 2 force member can be in equilibrium. Since the two forces acting on the member are equal and opposite, they cancel each other out, resulting in a net force of zero. This means that the member is in a state of equilibrium, where the sum of all forces acting on it is equal to zero.

5. How do 2 force members affect the overall stability of a truss?

2 force members play a crucial role in the stability of a truss structure. They help transfer the loads acting on the truss and prevent it from collapsing under external forces. Additionally, their presence helps maintain the rigidity and balance of the truss, making it more stable and able to withstand various loads.

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