Bending Moment & Neutral Axis: Why Not Centroid?

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SUMMARY

The discussion clarifies the relationship between the neutral axis and the centroid in structural mechanics, specifically in the context of bending moments in double I-beams. It establishes that the neutral axis does not coincide with the centroid when maximum bending moments occur, as this would imply no strain and no bending. The conversation emphasizes that strain refers to the elongation of a fiber, while the centroid is merely a geometric property, thus highlighting a fundamental misunderstanding in the original query.

PREREQUISITES
  • Understanding of bending moments in structural engineering
  • Knowledge of neutral axis concepts in beam theory
  • Familiarity with double I-beam structures
  • Basic principles of strain and stress in materials
NEXT STEPS
  • Research the mechanics of bending in beams, focusing on neutral axis behavior
  • Study the differences between strain and geometric properties in structural analysis
  • Explore the implications of maximum bending moments on beam design
  • Learn about the application of double I-beams in construction and their structural advantages
USEFUL FOR

Structural engineers, civil engineering students, and professionals involved in beam design and analysis will benefit from this discussion, particularly those looking to deepen their understanding of bending mechanics and material behavior under load.

knight92
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Hey guys, as the title says I can understand why the neutral axis does not pass through the centroid after reaching a point where the bending moment is max before the beam collapses. Say you have a straight structure supported by two double I-Beams and a weight in the middle. Why does the neutral axis not pass through the centroid, is it because the beams are simply bending ??

Cheers
 
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can't understand *
 


Your reference to "double I-beams" is not entirely clear. A picture would really help get your question across.
 


The strain is the distance of neutral axis from the line through centroid. If the neutral axis were at centroid, it would mean no strain and presumably, no bending.
 


"The strain is the distance of neutral axis from the line through centroid."

This statement is simply not true at all, and represents total confusion. It must be completely discounted. Strain describes the elongation of a fiber, while the centroid is a geometric property of an area.
 

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