Bar forces (1-6) should be calculated?

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In summary: That looks very wrong.In summary, the conversation is about calculating bar forces on a symmetrical framework with a left movable bearing. The person asking for help is not sure how to proceed, but their professor advised them to set the force in one direction and then calculate it to determine the correct direction. They provide their attempt at a solution and ask for help, but their calculations do not match the correct answer.
  • #1
Dan123
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Homework Statement


The pictue shows a symmetrical framework. I should calculate the bar forces. and make a "Clear Cut".I*m not shure because of the left movable bearing (on the left side)!?

1.jpg


Homework Equations


total x=0
total y=0
total M=0

The Attempt at a Solution


Here is my "Clear Cut" is it correctly?

2.jpg
 

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  • #2
You are right that the force at lower left acts at 45 degrees, but do you think it acts up or down on the frame?
 
  • #3
haruspex said:
You are right that the force at lower left acts at 45 degrees, but do you think it acts up or down on the frame?

I'm not shure, but our professor said, we should just set it in one direction, and after we calculate it we can see which the right direction was (if it is negative, we have to switch the direction).

But do you know, how I can solve this ...? I'm not shure
 
  • #4
Dan123 said:

Homework Statement


The pictue shows a symmetrical framework. I should calculate the bar forces. and make a "Clear Cut".I*m not shure because of the left movable bearing (on the left side)!?

View attachment 218785

Homework Equations


total x=0
total y=0
total M=0

The Attempt at a Solution


Here is my "Clear Cut" is it correctly?

View attachment 218786
i forgot...there is given

F, h, F1=2F and F2=3F
 
  • #5
Dan123 said:
our professor said, we should just set it in one direction, and after we calculate it we can see which the right direction was (if it is negative, we have to switch the direction).
That's correct, but it seemed you were asking for comments on your diagram.
Dan123 said:
how I can solve this
That's not what you asked originally. As per forum rules you need to show an attempt at a solution. Apply the relevant equations you quoted.
 
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  • #6
haruspex said:
That's correct, but it seemed you were asking for comments on your diagram.

That's not what you asked originally. As per forum rules you need to show an attempt at a solution. Apply the relevant equations you quoted.
ok, I will send my solution...or my try :)
 
  • #7
haruspex said:
That's correct, but it seemed you were asking for comments on your diagram.

That's not what you asked originally. As per forum rules you need to show an attempt at a solution. Apply the relevant equations you quoted.
So here is my try...I can't finish it...I don't get the right answer (the right answer is: S1=6F ; S2=(√5)/2 F ; S3=1,5F ; S4=7F ; S5=(√5)/2 F ; S6=1,5F )

IMG_20180123_203046_376.jpg


IMG_20180123_203116_656.jpg


I thought of dividing it in two parts (special calculation method...?!

Could you pplease help me :)
 

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  • #8
Dan123 said:
(the right answer is: S1=6F ; S2=(√5)/2 F ; S3=1,5F )
Doesn't look right to me.
I was suspicious that you may have specified the wrong values for the applied forces, so I made them arbitrary.
Consider the leftmost triangle and take moments about its lower right corner. Let N be the normal force from the lower left support, Gt the downward load at the top of the triangle, and Gr the load at the bottom right.
Take members 1 and 2 to be under compression, 3 under tension.
Y: N/√2-2S2/√5=Gr+Gt
X: N/√2=S2/√5-S3+S1
M: N/√2=Gt/2+S1
If I substitute the answers in the X and M equations I get N=5F√2, Gt=-F.
 
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1. What are bar forces (1-6) and why do they need to be calculated?

Bar forces (1-6) refer to the internal forces acting on a bar or structure. These forces are important to calculate because they help determine the stability and structural integrity of the bar.

2. How are bar forces (1-6) calculated?

Bar forces (1-6) can be calculated using various methods, such as the method of joints or method of sections. These methods involve analyzing the forces acting on each individual joint or section of the bar and using equations to calculate the resulting forces.

3. What factors can affect the calculation of bar forces (1-6)?

Several factors can influence the calculation of bar forces (1-6), including the material properties of the bar, the type and magnitude of external loads, and the geometry and shape of the bar.

4. How accurate are bar force calculations?

The accuracy of bar force calculations depends on the assumptions and simplifications made in the analysis. In most cases, these calculations provide a good estimate of the actual forces acting on the bar, but they may not be exact due to uncertainties and variations in real-world conditions.

5. Why is it important to double-check bar force calculations?

Double-checking bar force calculations is crucial to ensure the accuracy and safety of a structure. Mistakes in calculations can lead to structural failures and potential hazards. Therefore, it is important to carefully review and verify all calculations before using them in the design and construction of a bar or structure.

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