How to calculate tension/compression in a truss bridge (diagram shown)?

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Discussion Overview

The discussion revolves around calculating tension and compression forces in a truss bridge, particularly when a load is applied at the midpoint between two joints. Participants explore methods for analyzing the forces in the truss members, including the challenges posed by the configuration of the load and the presence of "X" trusses in the middle section.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant notes that forces like load and reaction force act on joints, questioning how to find forces on members when the load is centrally located.
  • Another participant suggests splitting the central force into two equal forces at the ends of the spar.
  • A participant expresses difficulty in calculating the forces in the middle section with "X" trusses and seeks assistance in determining the tension or compression in those members.
  • One contributor mentions that it is possible to assume a member is in tension or compression, indicating that a negative value would suggest an incorrect assumption.
  • Another participant advises against using the method of sections for the center load, recommending the method of joints instead and treating the load as a moment on the joint being analyzed.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the best method to analyze the forces in the truss members, with differing opinions on whether to use the method of sections or the method of joints. The discussion remains unresolved regarding the specific calculations and approaches to take.

Contextual Notes

Some participants express confusion about the calculations, particularly in relation to the middle section of the truss and the application of loads. There is also mention of potential assumptions that may affect the analysis.

enosthapa
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In general, in a truss diagram the forces like load, reaction force are act on joints but in this case the load is in the middle of two joints. How can I find forces on members in this case?

9qfdw6.jpg


Your help is really appreciated. Thank you for reading
 
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Since the force is in the center of the spar, you could split it into 2 5N forces at its ends...
 
Mech_Engineer said:
Since the force is in the center of the spar, you could split it into 2 5N forces at its ends...

Could you help me find out what force (tension/compression) do the truss members have please? I have done most of them but the middle section with "X" trusses are making it dificult to calculate the forces the carry...
 
346oy09.jpg

I have done some calculations to find out the forces but i am confused with the middle section. Can someone tell me if figure 2 is correct or not?Thank you
 
Last edited:
You can just assume one or the other (tension or compresison) and if you guessed wrong, you will get a negative value.
 
enosthapa said:
In general, in a truss diagram the forces like load, reaction force are act on joints but in this case the load is in the middle of two joints. How can I find forces on members in this case?

9qfdw6.jpg


Your help is really appreciated. Thank you for reading

Well, you can't use method of sections for the center... you'd have to use method of joints and treat that "external load" as a moment on the joint you're analyzing that's "connected" to the member that's loaded (as well as in force equilibrium)... seems as if the only two joints you'd concern yourself with with that center load are the ones to the left and right of it. at least that's how id attempt to do it. start at the supports and move your way towards the center.
 

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