Method of Sections: Ignored Forces?

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Discussion Overview

The discussion revolves around the application of the method of sections in truss analysis, specifically addressing the consideration of forces in beams that are not directly cut during the analysis. Participants explore whether internal forces in these beams should be accounted for in the method.

Discussion Character

  • Technical explanation, Debate/contested

Main Points Raised

  • One participant questions whether the method of sections inherently ignores forces in beams that are not being cut, such as beams AB and AH.
  • Another participant asserts that there are no external forces coming from the beams that are not cut.
  • A different participant acknowledges the absence of external forces but raises a concern about the neglect of internal forces, specifically questioning why force AH is not considered while force HG is.
  • In response, a participant clarifies that HG is not considered an internal force in the context of the current analysis and emphasizes the importance of splitting the structure into smaller parts, noting that some splits are effective while others may not be.

Areas of Agreement / Disagreement

Participants express differing views on the treatment of internal forces in the method of sections, indicating that the discussion remains unresolved regarding the inclusion of these forces.

Contextual Notes

The discussion highlights potential limitations in understanding the application of the method of sections, particularly regarding the definitions of internal and external forces and the effectiveness of different splitting strategies.

influx
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In the above example, the method of sections is used to solve the truss. However, they do not consider the forces in other beams (the beams that are not being cut; e.g. AB, AH). Is this always the case with this method?
 
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There are no external forces coming from those beams.
 
mfb said:
There are no external forces coming from those beams.

I understand but why are we not considering the internal forces eg force AH (like we are considering the internal force HG)
 
HG is not an internal force in this part. That's the idea - split the whole constructions in smaller parts. Some splittings work, some do not, this is a working one.
 

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