Problems involving trusses using method of joints

In summary, to solve for problems involving trusses using method of joints, you first need to make an intelligent guess as to which member is in compression and which is in tension. Then, you solve the equations, and if you guessed wrong, the force comes out negative. If you're still worried, show us a problem that you've done. Thanks for the help!
  • #1
Siddy3242
4
0
While solving for problems involving trusses using method of joints, how do i know which member is in compression and which is in tension?
any help would be appreciated, this stuff's been bugging me for quite some time

thanks and god bless
 
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  • #2
Welcome to PF!

Hi Siddy3242! Welcome to PF! :smile:
Siddy3242 said:
While solving for problems involving trusses using method of joints, how do i know which member is in compression and which is in tension?

You don't need to know …

the equations will come out negative one way, and positive the other …

in other words, make an intelligent guess as to whether it's in tension or compression, solve the equations, and if you guessed wrong, the force comes out negative! :biggrin:

If you're still worried, show us a problem that you've done. :smile:
 
  • #3


tiny-tim said:
Hi Siddy3242! Welcome to PF! :smile:


You don't need to know …

the equations will come out negative one way, and positive the other …

in other words, make an intelligent guess as to whether it's in tension or compression, solve the equations, and if you guessed wrong, the force comes out negative! :biggrin:

If you're still worried, show us a problem that you've done. :smile:

http://img122.imageshack.us/img122/5923/88374834wb5.jpg [Broken]

thats the problem i m working on

so far i have drawn the free body diagram of the truss
found the 2 horizontal forces in the 2 corner joints

right now i m starting from point A, and considering the first triangle ABC,
but like i said b4, i don't know nothing about the direction of forces
i am totally lost @ this point
 
Last edited by a moderator:
  • #4


nvm, i figured it out thanks a lot
i kinda have a new problem

i can't figure out where zero forces in trusses come into play, i mean how do i know which forces are zero force members or not?
 
  • #5
Siddy3242 said:
nvm, i figured it out thanks a lot
i kinda have a new problem

i can't figure out where zero forces in trusses come into play, i mean how do i know which forces are zero force members or not?

hmm … I've never come across zero forces :frown:

I assume you just solve the equations, and find that some members have positive force, which is tension, some have negative force, which is compression, and some have zero force … so they can just relax! :biggrin:
 
  • #6


tiny-tim said:
hmm … I've never come across zero forces :frown:

I assume you just solve the equations, and find that some members have positive force, which is tension, some have negative force, which is compression, and some have zero force … so they can just relax! :biggrin:

oh well, I have it almost figured out

thanks a lot anyways, u been a great help:smile:
 

1. What is the method of joints?

The method of joints is a technique used to solve problems involving trusses, which are structures composed of interconnected beams or members.

2. How does the method of joints work?

The method of joints works by analyzing the forces acting on each joint or connection point in a truss. By applying the principles of equilibrium and using free-body diagrams, the unknown forces at each joint can be determined.

3. When should the method of joints be used?

The method of joints should be used for statically determinate trusses, which are trusses that can be solved using only the principles of equilibrium. It is also useful for trusses with only a few members or for simple problems with symmetrical or repetitive patterns.

4. What are the limitations of the method of joints?

The method of joints can only be used for statically determinate trusses, as mentioned earlier. It also assumes that the joints are perfectly connected and that the members are idealized as weightless and rigid. In reality, joints can experience some level of friction or bending, and members may have their own weight and flexibility.

5. Can the method of joints be used for trusses with external forces?

Yes, the method of joints can be used for trusses with external forces, as long as they are in equilibrium and do not cause the truss to become statically indeterminate. In these cases, the external forces will also be included in the free-body diagrams of the joints, and their effects on the truss will be considered in the analysis.

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