How Do You Calculate Forces in a Truss Using the Method of Joints?

[naruto631]

Homework Statement

i am trying to figure out the forces of the different members of this truss in which looks like a a square that is split into two triangles and is affixed to another triangle the same size I have already found the moment of the reactions and already found the reaction forces as well.

  A -500lbf  C -500lbf

                              2ft           2ft
                            --------l----------- l Pin Reaction E
                              \         l          /     l
                                \       l        /       l   2ft
                                  \     l      /         l
                                    \   l    /           l
                                      \ l  /---------l Roller reaction D
                                        B

Homework Equations

sin
cos
tan
Efx=0
Efy=0
Em=0

The Attempt at a Solution

more or less it is a question about the method of joints but I am not exactly sure how you do it. Also the triangles are all 45° 45° and 90°

 

[NascentOxygen]

It is not clear, is your truss is made of 4 straight pieces, or 7? To what do the lbf refer?

If you wish to use ASCII art (and I don't recommend it), then you must include it within [code] [/code] pair. Otherwise the forum software squashes strings of spaces into a single space. You'll find it easiest if you also use Courier fixed-size font.

 [font="courier new"]
                       |
-----------------------|
\          |          /|
  \        |        /  |
    \      |      /    |
      \    |    /      |
        \  |  /        |
          \|/          |
-----------------------'
                                   [/font]

 

[naruto631]

thank you and your picture is pretty much accurate without that line extending after B though

 

[NascentOxygen]

Point B is unsupported and in mid-air, is it?

What and where are points A and C?

 

[DeeNos]

I would suggest using the method of joints to solve for the forces in the truss. This method involves analyzing the forces acting at each joint in the truss and using the equations of equilibrium (Efx=0, Efy=0, and Em=0) to solve for the unknown forces.

First, identify all the joints in the truss and label them with letters (A, B, C, D, E). Then, start at a joint with only two unknown forces and use the equations of equilibrium to solve for those forces. Continue this process at each joint until all the unknown forces in the truss are solved for.

Additionally, since all the triangles in the truss are 45° 45° and 90°, you can use the trigonometric functions (sin, cos, tan) to help solve for the forces.

It is also important to note that the moment of the reactions and the reaction forces have already been found, so they can be used as known values in the equations of equilibrium.

Overall, the method of joints is a systematic and reliable way to solve for the forces in a truss. Good luck with your calculations!