principle stress

[civil2013]

hi,
i know that principle stresses are the normal stresses acting on element when the element orientation is such that there is no shear stresses. as per text book, its nothing but the same normal stresses (in x,y) when the element rotattion is such that there is no shear stress on the element. but my basic doubt is when we do a finite element model, we define the element coordinates and when we get the normal stresses in that x,y direction, why shud i be interested in the normal stresses that would occur when the shear stress in zero. and so why shud i go for the normal stress that wud have resulted due to the rotation of element ?? is it bcos due to distortion of the fe model, the element will get deformed and so rotated and this normal stresses is reported as principle stresses.

thanks for the help in advance.

 

[bkal]

Why do you think you need to explore principle stresses?

You might be interested in principle stresses for a number of reasons, for example:
- to investigate main load paths, stress flow etc.
- to check if material strength has been exceeded (for some materials major principal stress is a good measure of its strength),
- etc.
What you have suggested as a reason (model distortion) does not look right.

 

[KootK]

X2. For most code check applications, principal stresses are not required.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.