Design of Eccentric Weld Joint

[senthil83]

I am Designing a Eccentric fillet weld group which is subjected to bending stress due to vertical force (Sigma 1) and axial stress due to horizontal force in perpendicular direction of weld ( sigma 2) and shear stress due to vertical force (Tv).

For finding out resulatant stress for the combined stress action i am using the formula sqrt(sigma1^2+sigma2^2+3Tv^2).
But i find in some books to find the resultant stress for fillet weld as sqrt(sigma1^2+sigma2^2+Tv^2)

only for butt weld design they are using the first relation, for fillet welds they are using second relation why?

 

[ishvaaag]

Why ... they are using different criteria for limit stress ... if they come from reliable sources, the pertinent criteria checked in the way quoted in the book or code states should be safe. I have seen your second formula in Pilkey's to check line welds (of whatever the kind, I assume, hence both fillet and butt welds, fillet uses extant throat widths or butt weld whole width following the case).

Your statement in the first paragraph maybe requires a sketch ... the vertical forces as usually drawn when producing longitudinal stresses from bending produce bending HORIZONTAL stresses, directly additive to your horizontal axial stress. So instead of sqrt(sigma1^2+sigma2^2+3Tv^2) one would have sqrt((sigmah1+sigmah2)^2+3Tv^2) that is a von Mises criterium, to apply to throat widths or full width if full weld.