Solving Equilateral Truss Force w/ Method of Sections

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In summary, the conversation is about finding the force in each member of an equilateral truss and using the equations sum Fy=0, sum Fx=0, and sum M=0 to solve the problem. The person giving advice suggests drawing to scale and making equilibrium statements about the free body diagram. They point out that the equation attempted ignored the contribution from AB.
  • #1
weedannycool
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Homework Statement



Find the force in each member of an equilateral truss. See figure.

Homework Equations



sum Fy=0
sum Fx=0
sum M=0

The Attempt at a Solution



first of all i tryed to cut through AB and AC and i off set the X/Y axis by rotating 30 degrees CCW then i did,

0=Fbc-735cos60

i thought i would get the right answer for Fbc but it is wrong.
Any thoughts?
 

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  • #2
First of all, try always to draw to scale, in order to avoid distorting the problem. Secondly, when you make a cut, as you have done, replace the cut ends with the forces that are "exposed", in direction if you don't know the magnitude. Then make equilibrium statements about the free body diagram that results, with all the horizontal and vertical components if necessary. In this case, are you able to sketch the triangle of forces at B, more or less to scale? The equation you attempted ignored the contribution from BC.
 
  • #3
Sorry, that last sentence should have said "The equation you attempted ignored the contribution from AB.
 

1. How do you determine the forces in an equilateral truss using the method of sections?

The method of sections involves cutting the truss into two parts and analyzing the forces in each section. To determine the forces in an equilateral truss, you will need to draw a free body diagram of the section, apply the equations of equilibrium, and solve for the unknown forces.

2. What are the equations of equilibrium used in the method of sections?

The equations of equilibrium used in the method of sections are the sum of forces in the x-direction, the sum of forces in the y-direction, and the sum of moments about any point. These equations ensure that the truss is in a state of static equilibrium.

3. Can the method of sections be used to solve for all the forces in an equilateral truss?

No, the method of sections can only be used to solve for the forces in a specific section of the truss. In an equilateral truss, there will be multiple sections that need to be analyzed to determine all the forces in the truss.

4. What are the advantages of using the method of sections to solve for truss forces?

The method of sections is a more efficient and accurate method compared to the method of joints. It allows for the determination of forces in individual sections, which can then be used to determine the forces in the entire truss. It also eliminates the need for solving simultaneous equations.

5. Are there any limitations to using the method of sections for solving truss forces?

Yes, the method of sections can only be used to solve for forces in statically determinate trusses, meaning trusses with a maximum of three unknown forces. It also assumes that the truss members are connected by frictionless pins and that the truss is loaded at the joints.

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