How do I find the force in each beam of a truss problem?

[Zaza669]

http://www.siz.co.il/my.php?i=oogytirin1tt.jpg

I have to find force in 1. 2. 3. 4. Beam.
How can i do that?

Thanks

 

[PhanthomJay]

What have you tried? Are you not familiar with method of joints?

 

[Zaza669]

No. I have to use Method of section. I have no idea how to cut the 4 beam together.

 

[PhanthomJay]

No. I have to use Method of section. I have no idea how to cut the 4 beam together.

Oh that's unfortunate. But you don't want to cut more than 3 members. Try looking at the left section of the truss cutting thru members 1, 2, and 3. Then sum moments about the lower left hand corner to solve for the force in member 3. Then you can use the sum of forces in x direction and in y direction = 0 to solve for for force in member 2 and 1. Force in member 4 should then be obvious maybe.

 

[Zaza669]

Oh that's unfortunate. But you don't want to cut more than 3 members. Try looking at the left section of the truss cutting thru members 1, 2, and 3. Then sum moments about the lower left hand corner to solve for the force in member 3. Then you can use the sum of forces in x direction and in y direction = 0 to solve for for force in member 2 and 1. Force in member 4 should then be obvious maybe.

Can you show me on the paper how to solve that?
Thanks

 

[PhanthomJay]

Can you show me on the paper how to solve that?
Thanks

You should become familiar with identifying zero force members. Otherwise, see attached. Sum moments about A to solve for F3. There's going to be a lot of zeroes in that equation...