Problems involving trusses using method of joints

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Discussion Overview

The discussion revolves around understanding the method of joints in solving problems involving trusses, specifically focusing on identifying whether truss members are in tension or compression and the concept of zero-force members. Participants share their experiences and seek clarification on these topics.

Discussion Character

  • Homework-related
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant expresses confusion about determining which truss members are in tension and which are in compression, seeking help on the topic.
  • Another participant suggests making an educated guess regarding the direction of forces, noting that solving the equations will reveal the correct nature of the forces, as negative results indicate an incorrect initial assumption.
  • A participant shares a specific problem they are working on and describes their progress, including drawing a free body diagram and calculating horizontal forces, but still feels uncertain about the direction of forces.
  • After some time, the original poster mentions they figured out the previous issue but encounters a new question regarding zero-force members in trusses.
  • Participants discuss the identification of zero-force members, with one expressing uncertainty about the concept and suggesting that solving the equations will indicate which members have zero force.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the identification of zero-force members, and there remains uncertainty regarding the application of the method of joints in determining tension and compression in truss members.

Contextual Notes

Some participants rely on assumptions about the equations and their outcomes, while others express a lack of familiarity with zero-force members, indicating potential gaps in understanding or experience.

Siddy3242
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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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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:​
 


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

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:


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?
 
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:
 


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:
 

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