Bending Moment & Neutral Axis: Why Not Centroid?

[knight92]

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

 

[knight92]

can't understand *

 

[OldEngr63]

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

 

[FAlonso]

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.

 

[OldEngr63]

"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.