Bending stresses in unsymmetrical sections

In case of unsymmetrical sections, neutral axis will not pass through the geometrical centre of the section. In unsymmetrical beam sections the distance of outermost layers i.e. for topmost layer and bottom layer of the section from neutral axis will not be same.

In order to calculate the bending stress for unsymmetrical sections, we must have to find the value of centre of gravity (centroid) of the given unsymmetrical section.

In order to calculate the maximum bending stress for unsymmetrical sections, we will use the bigger value of y.

In this section, the following notation will be use:

fbt = flexure stress of fiber in tension

fbc = flexure stress of fiber in compression

N.A. = neutral axis

I = Moment of Inertia about N.A

yt = distance of fiber in tension from N.A.

yc = distance of fiber in compression from N.A.

M = resisting moment

Mc = resisting moment in compression

Mt = resisting moment in tension

Max.flexure stress in tension fbt = (M/I).yt

Max.flexure stress in compression fbc = (M/I).yc

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Prof.Kodali Srinivas

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